tjh.dev / kernel
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kernel / arch / Kconfig
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1# SPDX-License-Identifier: GPL-2.0 2# 3# General architecture dependent options 4# 5 6# 7# Note: arch/$(SRCARCH)/Kconfig needs to be included first so that it can 8# override the default values in this file. 9# 10source "arch/$(SRCARCH)/Kconfig" 11 12config ARCH_CONFIGURES_CPU_MITIGATIONS 13 bool 14 15if !ARCH_CONFIGURES_CPU_MITIGATIONS 16config CPU_MITIGATIONS 17 def_bool y 18endif 19 20# 21# Selected by architectures that need custom DMA operations for e.g. legacy 22# IOMMUs not handled by dma-iommu. Drivers must never select this symbol. 23# 24config ARCH_HAS_DMA_OPS 25 depends on HAS_DMA 26 select DMA_OPS_HELPERS 27 bool 28 29menu "General architecture-dependent options" 30 31config ARCH_HAS_SUBPAGE_FAULTS 32 bool 33 help 34 Select if the architecture can check permissions at sub-page 35 granularity (e.g. arm64 MTE). The probe_user_*() functions 36 must be implemented. 37 38config HOTPLUG_SMT 39 bool 40 41config SMT_NUM_THREADS_DYNAMIC 42 bool 43 44config ARCH_SUPPORTS_SCHED_SMT 45 bool 46 47config ARCH_SUPPORTS_SCHED_CLUSTER 48 bool 49 50config ARCH_SUPPORTS_SCHED_MC 51 bool 52 53config SCHED_SMT 54 bool "SMT (Hyperthreading) scheduler support" 55 depends on ARCH_SUPPORTS_SCHED_SMT 56 default y 57 help 58 Improves the CPU scheduler's decision making when dealing with 59 MultiThreading at a cost of slightly increased overhead in some 60 places. If unsure say N here. 61 62config SCHED_CLUSTER 63 bool "Cluster scheduler support" 64 depends on ARCH_SUPPORTS_SCHED_CLUSTER 65 default y 66 help 67 Cluster scheduler support improves the CPU scheduler's decision 68 making when dealing with machines that have clusters of CPUs. 69 Cluster usually means a couple of CPUs which are placed closely 70 by sharing mid-level caches, last-level cache tags or internal 71 busses. 72 73config SCHED_MC 74 bool "Multi-Core Cache (MC) scheduler support" 75 depends on ARCH_SUPPORTS_SCHED_MC 76 default y 77 help 78 Multi-core scheduler support improves the CPU scheduler's decision 79 making when dealing with multi-core CPU chips at a cost of slightly 80 increased overhead in some places. If unsure say N here. 81 82# Selected by HOTPLUG_CORE_SYNC_DEAD or HOTPLUG_CORE_SYNC_FULL 83config HOTPLUG_CORE_SYNC 84 bool 85 86# Basic CPU dead synchronization selected by architecture 87config HOTPLUG_CORE_SYNC_DEAD 88 bool 89 select HOTPLUG_CORE_SYNC 90 91# Full CPU synchronization with alive state selected by architecture 92config HOTPLUG_CORE_SYNC_FULL 93 bool 94 select HOTPLUG_CORE_SYNC_DEAD if HOTPLUG_CPU 95 select HOTPLUG_CORE_SYNC 96 97config HOTPLUG_SPLIT_STARTUP 98 bool 99 select HOTPLUG_CORE_SYNC_FULL 100 101config HOTPLUG_PARALLEL 102 bool 103 select HOTPLUG_SPLIT_STARTUP 104 105config GENERIC_IRQ_ENTRY 106 bool 107 108config GENERIC_SYSCALL 109 bool 110 depends on GENERIC_IRQ_ENTRY 111 112config GENERIC_ENTRY 113 bool 114 select GENERIC_IRQ_ENTRY 115 select GENERIC_SYSCALL 116 117config KPROBES 118 bool "Kprobes" 119 depends on HAVE_KPROBES 120 select KALLSYMS 121 select EXECMEM 122 select NEED_TASKS_RCU 123 help 124 Kprobes allows you to trap at almost any kernel address and 125 execute a callback function. register_kprobe() establishes 126 a probepoint and specifies the callback. Kprobes is useful 127 for kernel debugging, non-intrusive instrumentation and testing. 128 If in doubt, say "N". 129 130config JUMP_LABEL 131 bool "Optimize very unlikely/likely branches" 132 depends on HAVE_ARCH_JUMP_LABEL 133 select OBJTOOL if HAVE_JUMP_LABEL_HACK 134 help 135 This option enables a transparent branch optimization that 136 makes certain almost-always-true or almost-always-false branch 137 conditions even cheaper to execute within the kernel. 138 139 Certain performance-sensitive kernel code, such as trace points, 140 scheduler functionality, networking code and KVM have such 141 branches and include support for this optimization technique. 142 143 If it is detected that the compiler has support for "asm goto", 144 the kernel will compile such branches with just a nop 145 instruction. When the condition flag is toggled to true, the 146 nop will be converted to a jump instruction to execute the 147 conditional block of instructions. 148 149 This technique lowers overhead and stress on the branch prediction 150 of the processor and generally makes the kernel faster. The update 151 of the condition is slower, but those are always very rare. 152 153 ( On 32-bit x86, the necessary options added to the compiler 154 flags may increase the size of the kernel slightly. ) 155 156config STATIC_KEYS_SELFTEST 157 bool "Static key selftest" 158 depends on JUMP_LABEL 159 help 160 Boot time self-test of the branch patching code. 161 162config STATIC_CALL_SELFTEST 163 bool "Static call selftest" 164 depends on HAVE_STATIC_CALL 165 help 166 Boot time self-test of the call patching code. 167 168config OPTPROBES 169 def_bool y 170 depends on KPROBES && HAVE_OPTPROBES 171 select NEED_TASKS_RCU 172 173config KPROBES_ON_FTRACE 174 def_bool y 175 depends on KPROBES && HAVE_KPROBES_ON_FTRACE 176 depends on DYNAMIC_FTRACE_WITH_REGS 177 help 178 If function tracer is enabled and the arch supports full 179 passing of pt_regs to function tracing, then kprobes can 180 optimize on top of function tracing. 181 182config UPROBES 183 def_bool n 184 depends on ARCH_SUPPORTS_UPROBES 185 select TASKS_TRACE_RCU 186 help 187 Uprobes is the user-space counterpart to kprobes: they 188 enable instrumentation applications (such as 'perf probe') 189 to establish unintrusive probes in user-space binaries and 190 libraries, by executing handler functions when the probes 191 are hit by user-space applications. 192 193 ( These probes come in the form of single-byte breakpoints, 194 managed by the kernel and kept transparent to the probed 195 application. ) 196 197config HAVE_64BIT_ALIGNED_ACCESS 198 def_bool 64BIT && !HAVE_EFFICIENT_UNALIGNED_ACCESS 199 help 200 Some architectures require 64 bit accesses to be 64 bit 201 aligned, which also requires structs containing 64 bit values 202 to be 64 bit aligned too. This includes some 32 bit 203 architectures which can do 64 bit accesses, as well as 64 bit 204 architectures without unaligned access. 205 206 This symbol should be selected by an architecture if 64 bit 207 accesses are required to be 64 bit aligned in this way even 208 though it is not a 64 bit architecture. 209 210 See Documentation/core-api/unaligned-memory-access.rst for 211 more information on the topic of unaligned memory accesses. 212 213config HAVE_EFFICIENT_UNALIGNED_ACCESS 214 bool 215 help 216 Some architectures are unable to perform unaligned accesses 217 without the use of get_unaligned/put_unaligned. Others are 218 unable to perform such accesses efficiently (e.g. trap on 219 unaligned access and require fixing it up in the exception 220 handler.) 221 222 This symbol should be selected by an architecture if it can 223 perform unaligned accesses efficiently to allow different 224 code paths to be selected for these cases. Some network 225 drivers, for example, could opt to not fix up alignment 226 problems with received packets if doing so would not help 227 much. 228 229 See Documentation/core-api/unaligned-memory-access.rst for more 230 information on the topic of unaligned memory accesses. 231 232config ARCH_USE_BUILTIN_BSWAP 233 bool 234 help 235 Modern versions of GCC (since 4.4) have builtin functions 236 for handling byte-swapping. Using these, instead of the old 237 inline assembler that the architecture code provides in the 238 __arch_bswapXX() macros, allows the compiler to see what's 239 happening and offers more opportunity for optimisation. In 240 particular, the compiler will be able to combine the byteswap 241 with a nearby load or store and use load-and-swap or 242 store-and-swap instructions if the architecture has them. It 243 should almost *never* result in code which is worse than the 244 hand-coded assembler in <asm/swab.h>. But just in case it 245 does, the use of the builtins is optional. 246 247 Any architecture with load-and-swap or store-and-swap 248 instructions should set this. And it shouldn't hurt to set it 249 on architectures that don't have such instructions. 250 251config KRETPROBES 252 def_bool y 253 depends on KPROBES && (HAVE_KRETPROBES || HAVE_RETHOOK) 254 255config KRETPROBE_ON_RETHOOK 256 def_bool y 257 depends on HAVE_RETHOOK 258 depends on KRETPROBES 259 select RETHOOK 260 261config USER_RETURN_NOTIFIER 262 bool 263 depends on HAVE_USER_RETURN_NOTIFIER 264 help 265 Provide a kernel-internal notification when a cpu is about to 266 switch to user mode. 267 268config HAVE_IOREMAP_PROT 269 bool 270 271config HAVE_KPROBES 272 bool 273 274config HAVE_KRETPROBES 275 bool 276 277config HAVE_OPTPROBES 278 bool 279 280config HAVE_KPROBES_ON_FTRACE 281 bool 282 283config ARCH_CORRECT_STACKTRACE_ON_KRETPROBE 284 bool 285 help 286 Since kretprobes modifies return address on the stack, the 287 stacktrace may see the kretprobe trampoline address instead 288 of correct one. If the architecture stacktrace code and 289 unwinder can adjust such entries, select this configuration. 290 291config HAVE_FUNCTION_ERROR_INJECTION 292 bool 293 294config HAVE_NMI 295 bool 296 297config HAVE_FUNCTION_DESCRIPTORS 298 bool 299 300config TRACE_IRQFLAGS_SUPPORT 301 bool 302 303config TRACE_IRQFLAGS_NMI_SUPPORT 304 bool 305 306# 307# An arch should select this if it provides all these things: 308# 309# task_pt_regs() in asm/processor.h or asm/ptrace.h 310# arch_has_single_step() if there is hardware single-step support 311# arch_has_block_step() if there is hardware block-step support 312# asm/syscall.h supplying asm-generic/syscall.h interface 313# linux/regset.h user_regset interfaces 314# CORE_DUMP_USE_REGSET #define'd in linux/elf.h 315# TIF_SYSCALL_TRACE calls ptrace_report_syscall_{entry,exit} 316# TIF_NOTIFY_RESUME calls resume_user_mode_work() 317# 318config HAVE_ARCH_TRACEHOOK 319 bool 320 321config HAVE_DMA_CONTIGUOUS 322 bool 323 324config GENERIC_SMP_IDLE_THREAD 325 bool 326 327config GENERIC_IDLE_POLL_SETUP 328 bool 329 330config ARCH_HAS_FORTIFY_SOURCE 331 bool 332 help 333 An architecture should select this when it can successfully 334 build and run with CONFIG_FORTIFY_SOURCE. 335 336# 337# Select if the arch provides a historic keepinit alias for the retain_initrd 338# command line option 339# 340config ARCH_HAS_KEEPINITRD 341 bool 342 343# Select if arch has all set_memory_ro/rw/x/nx() functions in asm/cacheflush.h 344config ARCH_HAS_SET_MEMORY 345 bool 346 347# Select if arch has all set_direct_map_invalid/default() functions 348config ARCH_HAS_SET_DIRECT_MAP 349 bool 350 351# 352# Select if the architecture provides the arch_dma_set_uncached symbol to 353# either provide an uncached segment alias for a DMA allocation, or 354# to remap the page tables in place. 355# 356config ARCH_HAS_DMA_SET_UNCACHED 357 bool 358 359# 360# Select if the architectures provides the arch_dma_clear_uncached symbol 361# to undo an in-place page table remap for uncached access. 362# 363config ARCH_HAS_DMA_CLEAR_UNCACHED 364 bool 365 366config ARCH_HAS_CPU_FINALIZE_INIT 367 bool 368 369# The architecture has a per-task state that includes the mm's PASID 370config ARCH_HAS_CPU_PASID 371 bool 372 select IOMMU_MM_DATA 373 374config HAVE_ARCH_THREAD_STRUCT_WHITELIST 375 bool 376 help 377 An architecture should select this to provide hardened usercopy 378 knowledge about what region of the thread_struct should be 379 whitelisted for copying to userspace. Normally this is only the 380 FPU registers. Specifically, arch_thread_struct_whitelist() 381 should be implemented. Without this, the entire thread_struct 382 field in task_struct will be left whitelisted. 383 384# Select if arch wants to size task_struct dynamically via arch_task_struct_size: 385config ARCH_WANTS_DYNAMIC_TASK_STRUCT 386 bool 387 388config ARCH_WANTS_NO_INSTR 389 bool 390 help 391 An architecture should select this if the noinstr macro is being used on 392 functions to denote that the toolchain should avoid instrumenting such 393 functions and is required for correctness. 394 395config ARCH_32BIT_OFF_T 396 bool 397 depends on !64BIT 398 help 399 All new 32-bit architectures should have 64-bit off_t type on 400 userspace side which corresponds to the loff_t kernel type. This 401 is the requirement for modern ABIs. Some existing architectures 402 still support 32-bit off_t. This option is enabled for all such 403 architectures explicitly. 404 405# Selected by 64 bit architectures which have a 32 bit f_tinode in struct ustat 406config ARCH_32BIT_USTAT_F_TINODE 407 bool 408 409config HAVE_ASM_MODVERSIONS 410 bool 411 help 412 This symbol should be selected by an architecture if it provides 413 <asm/asm-prototypes.h> to support the module versioning for symbols 414 exported from assembly code. 415 416config HAVE_REGS_AND_STACK_ACCESS_API 417 bool 418 help 419 This symbol should be selected by an architecture if it supports 420 the API needed to access registers and stack entries from pt_regs, 421 declared in asm/ptrace.h 422 For example the kprobes-based event tracer needs this API. 423 424config HAVE_RSEQ 425 bool 426 depends on HAVE_REGS_AND_STACK_ACCESS_API 427 help 428 This symbol should be selected by an architecture if it 429 supports an implementation of restartable sequences. 430 431config HAVE_RUST 432 bool 433 help 434 This symbol should be selected by an architecture if it 435 supports Rust. 436 437config HAVE_FUNCTION_ARG_ACCESS_API 438 bool 439 help 440 This symbol should be selected by an architecture if it supports 441 the API needed to access function arguments from pt_regs, 442 declared in asm/ptrace.h 443 444config HAVE_HW_BREAKPOINT 445 bool 446 depends on PERF_EVENTS 447 448config HAVE_MIXED_BREAKPOINTS_REGS 449 bool 450 depends on HAVE_HW_BREAKPOINT 451 help 452 Depending on the arch implementation of hardware breakpoints, 453 some of them have separate registers for data and instruction 454 breakpoints addresses, others have mixed registers to store 455 them but define the access type in a control register. 456 Select this option if your arch implements breakpoints under the 457 latter fashion. 458 459config HAVE_USER_RETURN_NOTIFIER 460 bool 461 462config HAVE_PERF_EVENTS_NMI 463 bool 464 help 465 System hardware can generate an NMI using the perf event 466 subsystem. Also has support for calculating CPU cycle events 467 to determine how many clock cycles in a given period. 468 469config HAVE_HARDLOCKUP_DETECTOR_PERF 470 bool 471 depends on HAVE_PERF_EVENTS_NMI 472 help 473 The arch chooses to use the generic perf-NMI-based hardlockup 474 detector. Must define HAVE_PERF_EVENTS_NMI. 475 476config HAVE_HARDLOCKUP_DETECTOR_ARCH 477 bool 478 help 479 The arch provides its own hardlockup detector implementation instead 480 of the generic ones. 481 482 It uses the same command line parameters, and sysctl interface, 483 as the generic hardlockup detectors. 484 485config UNWIND_USER 486 bool 487 488config HAVE_UNWIND_USER_FP 489 bool 490 select UNWIND_USER 491 492config HAVE_PERF_REGS 493 bool 494 help 495 Support selective register dumps for perf events. This includes 496 bit-mapping of each registers and a unique architecture id. 497 498config HAVE_PERF_USER_STACK_DUMP 499 bool 500 help 501 Support user stack dumps for perf event samples. This needs 502 access to the user stack pointer which is not unified across 503 architectures. 504 505config HAVE_ARCH_JUMP_LABEL 506 bool 507 508config HAVE_ARCH_JUMP_LABEL_RELATIVE 509 bool 510 511config MMU_GATHER_TABLE_FREE 512 bool 513 514config MMU_GATHER_RCU_TABLE_FREE 515 bool 516 select MMU_GATHER_TABLE_FREE 517 518config MMU_GATHER_PAGE_SIZE 519 bool 520 521config MMU_GATHER_NO_RANGE 522 bool 523 select MMU_GATHER_MERGE_VMAS 524 525config MMU_GATHER_NO_FLUSH_CACHE 526 bool 527 528config MMU_GATHER_MERGE_VMAS 529 bool 530 531config MMU_GATHER_NO_GATHER 532 bool 533 depends on MMU_GATHER_TABLE_FREE 534 535config ARCH_WANT_IRQS_OFF_ACTIVATE_MM 536 bool 537 help 538 Temporary select until all architectures can be converted to have 539 irqs disabled over activate_mm. Architectures that do IPI based TLB 540 shootdowns should enable this. 541 542# Use normal mm refcounting for MMU_LAZY_TLB kernel thread references. 543# MMU_LAZY_TLB_REFCOUNT=n can improve the scalability of context switching 544# to/from kernel threads when the same mm is running on a lot of CPUs (a large 545# multi-threaded application), by reducing contention on the mm refcount. 546# 547# This can be disabled if the architecture ensures no CPUs are using an mm as a 548# "lazy tlb" beyond its final refcount (i.e., by the time __mmdrop frees the mm 549# or its kernel page tables). This could be arranged by arch_exit_mmap(), or 550# final exit(2) TLB flush, for example. 551# 552# To implement this, an arch *must*: 553# Ensure the _lazy_tlb variants of mmgrab/mmdrop are used when manipulating 554# the lazy tlb reference of a kthread's ->active_mm (non-arch code has been 555# converted already). 556config MMU_LAZY_TLB_REFCOUNT 557 def_bool y 558 depends on !MMU_LAZY_TLB_SHOOTDOWN 559 560# This option allows MMU_LAZY_TLB_REFCOUNT=n. It ensures no CPUs are using an 561# mm as a lazy tlb beyond its last reference count, by shooting down these 562# users before the mm is deallocated. __mmdrop() first IPIs all CPUs that may 563# be using the mm as a lazy tlb, so that they may switch themselves to using 564# init_mm for their active mm. mm_cpumask(mm) is used to determine which CPUs 565# may be using mm as a lazy tlb mm. 566# 567# To implement this, an arch *must*: 568# - At the time of the final mmdrop of the mm, ensure mm_cpumask(mm) contains 569# at least all possible CPUs in which the mm is lazy. 570# - It must meet the requirements for MMU_LAZY_TLB_REFCOUNT=n (see above). 571config MMU_LAZY_TLB_SHOOTDOWN 572 bool 573 574config ARCH_HAVE_NMI_SAFE_CMPXCHG 575 bool 576 577config ARCH_HAVE_EXTRA_ELF_NOTES 578 bool 579 help 580 An architecture should select this in order to enable adding an 581 arch-specific ELF note section to core files. It must provide two 582 functions: elf_coredump_extra_notes_size() and 583 elf_coredump_extra_notes_write() which are invoked by the ELF core 584 dumper. 585 586config ARCH_HAS_NMI_SAFE_THIS_CPU_OPS 587 bool 588 589config HAVE_ALIGNED_STRUCT_PAGE 590 bool 591 help 592 This makes sure that struct pages are double word aligned and that 593 e.g. the SLUB allocator can perform double word atomic operations 594 on a struct page for better performance. However selecting this 595 might increase the size of a struct page by a word. 596 597config HAVE_CMPXCHG_LOCAL 598 bool 599 600config HAVE_CMPXCHG_DOUBLE 601 bool 602 603config ARCH_WEAK_RELEASE_ACQUIRE 604 bool 605 606config ARCH_WANT_IPC_PARSE_VERSION 607 bool 608 609config ARCH_WANT_COMPAT_IPC_PARSE_VERSION 610 bool 611 612config ARCH_WANT_OLD_COMPAT_IPC 613 select ARCH_WANT_COMPAT_IPC_PARSE_VERSION 614 bool 615 616config HAVE_ARCH_SECCOMP 617 bool 618 help 619 An arch should select this symbol to support seccomp mode 1 (the fixed 620 syscall policy), and must provide an overrides for __NR_seccomp_sigreturn, 621 and compat syscalls if the asm-generic/seccomp.h defaults need adjustment: 622 - __NR_seccomp_read_32 623 - __NR_seccomp_write_32 624 - __NR_seccomp_exit_32 625 - __NR_seccomp_sigreturn_32 626 627config HAVE_ARCH_SECCOMP_FILTER 628 bool 629 select HAVE_ARCH_SECCOMP 630 help 631 An arch should select this symbol if it provides all of these things: 632 - all the requirements for HAVE_ARCH_SECCOMP 633 - syscall_get_arch() 634 - syscall_get_arguments() 635 - syscall_rollback() 636 - syscall_set_return_value() 637 - SIGSYS siginfo_t support 638 - secure_computing is called from a ptrace_event()-safe context 639 - secure_computing return value is checked and a return value of -1 640 results in the system call being skipped immediately. 641 - seccomp syscall wired up 642 - if !HAVE_SPARSE_SYSCALL_NR, have SECCOMP_ARCH_NATIVE, 643 SECCOMP_ARCH_NATIVE_NR, SECCOMP_ARCH_NATIVE_NAME defined. If 644 COMPAT is supported, have the SECCOMP_ARCH_COMPAT* defines too. 645 646config SECCOMP 647 prompt "Enable seccomp to safely execute untrusted bytecode" 648 def_bool y 649 depends on HAVE_ARCH_SECCOMP 650 help 651 This kernel feature is useful for number crunching applications 652 that may need to handle untrusted bytecode during their 653 execution. By using pipes or other transports made available 654 to the process as file descriptors supporting the read/write 655 syscalls, it's possible to isolate those applications in their 656 own address space using seccomp. Once seccomp is enabled via 657 prctl(PR_SET_SECCOMP) or the seccomp() syscall, it cannot be 658 disabled and the task is only allowed to execute a few safe 659 syscalls defined by each seccomp mode. 660 661 If unsure, say Y. 662 663config SECCOMP_FILTER 664 def_bool y 665 depends on HAVE_ARCH_SECCOMP_FILTER && SECCOMP && NET 666 help 667 Enable tasks to build secure computing environments defined 668 in terms of Berkeley Packet Filter programs which implement 669 task-defined system call filtering polices. 670 671 See Documentation/userspace-api/seccomp_filter.rst for details. 672 673config SECCOMP_CACHE_DEBUG 674 bool "Show seccomp filter cache status in /proc/pid/seccomp_cache" 675 depends on SECCOMP_FILTER && !HAVE_SPARSE_SYSCALL_NR 676 depends on PROC_FS 677 help 678 This enables the /proc/pid/seccomp_cache interface to monitor 679 seccomp cache data. The file format is subject to change. Reading 680 the file requires CAP_SYS_ADMIN. 681 682 This option is for debugging only. Enabling presents the risk that 683 an adversary may be able to infer the seccomp filter logic. 684 685 If unsure, say N. 686 687config HAVE_ARCH_KSTACK_ERASE 688 bool 689 help 690 An architecture should select this if it has the code which 691 fills the used part of the kernel stack with the KSTACK_ERASE_POISON 692 value before returning from system calls. 693 694config HAVE_STACKPROTECTOR 695 bool 696 help 697 An arch should select this symbol if: 698 - it has implemented a stack canary (e.g. __stack_chk_guard) 699 700config STACKPROTECTOR 701 bool "Stack Protector buffer overflow detection" 702 depends on HAVE_STACKPROTECTOR 703 depends on $(cc-option,-fstack-protector) 704 default y 705 help 706 This option turns on the "stack-protector" GCC feature. This 707 feature puts, at the beginning of functions, a canary value on 708 the stack just before the return address, and validates 709 the value just before actually returning. Stack based buffer 710 overflows (that need to overwrite this return address) now also 711 overwrite the canary, which gets detected and the attack is then 712 neutralized via a kernel panic. 713 714 Functions will have the stack-protector canary logic added if they 715 have an 8-byte or larger character array on the stack. 716 717 This feature requires gcc version 4.2 or above, or a distribution 718 gcc with the feature backported ("-fstack-protector"). 719 720 On an x86 "defconfig" build, this feature adds canary checks to 721 about 3% of all kernel functions, which increases kernel code size 722 by about 0.3%. 723 724config STACKPROTECTOR_STRONG 725 bool "Strong Stack Protector" 726 depends on STACKPROTECTOR 727 depends on $(cc-option,-fstack-protector-strong) 728 default y 729 help 730 Functions will have the stack-protector canary logic added in any 731 of the following conditions: 732 733 - local variable's address used as part of the right hand side of an 734 assignment or function argument 735 - local variable is an array (or union containing an array), 736 regardless of array type or length 737 - uses register local variables 738 739 This feature requires gcc version 4.9 or above, or a distribution 740 gcc with the feature backported ("-fstack-protector-strong"). 741 742 On an x86 "defconfig" build, this feature adds canary checks to 743 about 20% of all kernel functions, which increases the kernel code 744 size by about 2%. 745 746config ARCH_SUPPORTS_SHADOW_CALL_STACK 747 bool 748 help 749 An architecture should select this if it supports the compiler's 750 Shadow Call Stack and implements runtime support for shadow stack 751 switching. 752 753config SHADOW_CALL_STACK 754 bool "Shadow Call Stack" 755 depends on ARCH_SUPPORTS_SHADOW_CALL_STACK 756 depends on DYNAMIC_FTRACE_WITH_ARGS || DYNAMIC_FTRACE_WITH_REGS || !FUNCTION_GRAPH_TRACER 757 depends on MMU 758 help 759 This option enables the compiler's Shadow Call Stack, which 760 uses a shadow stack to protect function return addresses from 761 being overwritten by an attacker. More information can be found 762 in the compiler's documentation: 763 764 - Clang: https://clang.llvm.org/docs/ShadowCallStack.html 765 - GCC: https://gcc.gnu.org/onlinedocs/gcc/Instrumentation-Options.html#Instrumentation-Options 766 767 Note that security guarantees in the kernel differ from the 768 ones documented for user space. The kernel must store addresses 769 of shadow stacks in memory, which means an attacker capable of 770 reading and writing arbitrary memory may be able to locate them 771 and hijack control flow by modifying the stacks. 772 773config DYNAMIC_SCS 774 bool 775 help 776 Set by the arch code if it relies on code patching to insert the 777 shadow call stack push and pop instructions rather than on the 778 compiler. 779 780config LTO 781 bool 782 help 783 Selected if the kernel will be built using the compiler's LTO feature. 784 785config LTO_CLANG 786 bool 787 select LTO 788 help 789 Selected if the kernel will be built using Clang's LTO feature. 790 791config ARCH_SUPPORTS_LTO_CLANG 792 bool 793 help 794 An architecture should select this option if it supports: 795 - compiling with Clang, 796 - compiling inline assembly with Clang's integrated assembler, 797 - and linking with LLD. 798 799config ARCH_SUPPORTS_LTO_CLANG_THIN 800 bool 801 help 802 An architecture should select this option if it can support Clang's 803 ThinLTO mode. 804 805config HAS_LTO_CLANG 806 def_bool y 807 depends on CC_IS_CLANG && LD_IS_LLD && AS_IS_LLVM 808 depends on $(success,$(NM) --help | head -n 1 | grep -qi llvm) 809 depends on $(success,$(AR) --help | head -n 1 | grep -qi llvm) 810 depends on ARCH_SUPPORTS_LTO_CLANG 811 depends on !FTRACE_MCOUNT_USE_RECORDMCOUNT 812 # https://github.com/ClangBuiltLinux/linux/issues/1721 813 depends on (!KASAN || KASAN_HW_TAGS || CLANG_VERSION >= 170000) || !DEBUG_INFO 814 depends on (!KCOV || CLANG_VERSION >= 170000) || !DEBUG_INFO 815 depends on !GCOV_KERNEL 816 help 817 The compiler and Kconfig options support building with Clang's 818 LTO. 819 820choice 821 prompt "Link Time Optimization (LTO)" 822 default LTO_NONE 823 help 824 This option enables Link Time Optimization (LTO), which allows the 825 compiler to optimize binaries globally. 826 827 If unsure, select LTO_NONE. Note that LTO is very resource-intensive 828 so it's disabled by default. 829 830config LTO_NONE 831 bool "None" 832 help 833 Build the kernel normally, without Link Time Optimization (LTO). 834 835config LTO_CLANG_FULL 836 bool "Clang Full LTO (EXPERIMENTAL)" 837 depends on HAS_LTO_CLANG 838 depends on !COMPILE_TEST 839 select LTO_CLANG 840 help 841 This option enables Clang's full Link Time Optimization (LTO), which 842 allows the compiler to optimize the kernel globally. If you enable 843 this option, the compiler generates LLVM bitcode instead of ELF 844 object files, and the actual compilation from bitcode happens at 845 the LTO link step, which may take several minutes depending on the 846 kernel configuration. More information can be found from LLVM's 847 documentation: 848 849 https://llvm.org/docs/LinkTimeOptimization.html 850 851 During link time, this option can use a large amount of RAM, and 852 may take much longer than the ThinLTO option. 853 854config LTO_CLANG_THIN 855 bool "Clang ThinLTO (EXPERIMENTAL)" 856 depends on HAS_LTO_CLANG && ARCH_SUPPORTS_LTO_CLANG_THIN 857 select LTO_CLANG 858 help 859 This option enables Clang's ThinLTO, which allows for parallel 860 optimization and faster incremental compiles compared to the 861 CONFIG_LTO_CLANG_FULL option. More information can be found 862 from Clang's documentation: 863 864 https://clang.llvm.org/docs/ThinLTO.html 865 866 If unsure, say Y. 867endchoice 868 869config ARCH_SUPPORTS_AUTOFDO_CLANG 870 bool 871 872config AUTOFDO_CLANG 873 bool "Enable Clang's AutoFDO build (EXPERIMENTAL)" 874 depends on ARCH_SUPPORTS_AUTOFDO_CLANG 875 depends on CC_IS_CLANG && CLANG_VERSION >= 170000 876 help 877 This option enables Clang’s AutoFDO build. When 878 an AutoFDO profile is specified in variable 879 CLANG_AUTOFDO_PROFILE during the build process, 880 Clang uses the profile to optimize the kernel. 881 882 If no profile is specified, AutoFDO options are 883 still passed to Clang to facilitate the collection 884 of perf data for creating an AutoFDO profile in 885 subsequent builds. 886 887 If unsure, say N. 888 889config ARCH_SUPPORTS_PROPELLER_CLANG 890 bool 891 892config PROPELLER_CLANG 893 bool "Enable Clang's Propeller build" 894 depends on ARCH_SUPPORTS_PROPELLER_CLANG 895 depends on CC_IS_CLANG && CLANG_VERSION >= 190000 896 help 897 This option enables Clang’s Propeller build. When the Propeller 898 profiles is specified in variable CLANG_PROPELLER_PROFILE_PREFIX 899 during the build process, Clang uses the profiles to optimize 900 the kernel. 901 902 If no profile is specified, Propeller options are still passed 903 to Clang to facilitate the collection of perf data for creating 904 the Propeller profiles in subsequent builds. 905 906 If unsure, say N. 907 908config ARCH_SUPPORTS_CFI 909 bool 910 help 911 An architecture should select this option if it can support Kernel 912 Control-Flow Integrity (CFI) checking (-fsanitize=kcfi). 913 914config ARCH_USES_CFI_TRAPS 915 bool 916 help 917 An architecture should select this option if it requires the 918 .kcfi_traps section for KCFI trap handling. 919 920config ARCH_USES_CFI_GENERIC_LLVM_PASS 921 bool 922 help 923 An architecture should select this option if it uses the generic 924 KCFIPass in LLVM to expand kCFI bundles instead of architecture-specific 925 lowering. 926 927config CFI 928 bool "Use Kernel Control Flow Integrity (kCFI)" 929 default CFI_CLANG 930 depends on ARCH_SUPPORTS_CFI 931 depends on $(cc-option,-fsanitize=kcfi) 932 help 933 This option enables forward-edge Control Flow Integrity (CFI) 934 checking, where the compiler injects a runtime check to each 935 indirect function call to ensure the target is a valid function with 936 the correct static type. This restricts possible call targets and 937 makes it more difficult for an attacker to exploit bugs that allow 938 the modification of stored function pointers. More information can be 939 found from Clang's documentation: 940 941 https://clang.llvm.org/docs/ControlFlowIntegrity.html 942 943config CFI_CLANG 944 bool 945 transitional 946 help 947 Transitional config for CFI_CLANG to CFI migration. 948 949config CFI_ICALL_NORMALIZE_INTEGERS 950 bool "Normalize CFI tags for integers" 951 depends on CFI 952 depends on HAVE_CFI_ICALL_NORMALIZE_INTEGERS 953 help 954 This option normalizes the CFI tags for integer types so that all 955 integer types of the same size and signedness receive the same CFI 956 tag. 957 958 The option is separate from CONFIG_RUST because it affects the ABI. 959 When working with build systems that care about the ABI, it is 960 convenient to be able to turn on this flag first, before Rust is 961 turned on. 962 963 This option is necessary for using CFI with Rust. If unsure, say N. 964 965config HAVE_CFI_ICALL_NORMALIZE_INTEGERS 966 def_bool y 967 depends on $(cc-option,-fsanitize=kcfi -fsanitize-cfi-icall-experimental-normalize-integers) 968 # With GCOV/KASAN we need this fix: https://github.com/llvm/llvm-project/pull/104826 969 depends on CLANG_VERSION >= 190103 || (!GCOV_KERNEL && !KASAN_GENERIC && !KASAN_SW_TAGS) 970 971config HAVE_CFI_ICALL_NORMALIZE_INTEGERS_RUSTC 972 def_bool y 973 depends on HAVE_CFI_ICALL_NORMALIZE_INTEGERS 974 depends on RUSTC_VERSION >= 107900 975 depends on ARM64 || X86_64 976 # With GCOV/KASAN we need this fix: https://github.com/rust-lang/rust/pull/129373 977 depends on (RUSTC_LLVM_VERSION >= 190103 && RUSTC_VERSION >= 108200) || \ 978 (!GCOV_KERNEL && !KASAN_GENERIC && !KASAN_SW_TAGS) 979 980config CFI_PERMISSIVE 981 bool "Use CFI in permissive mode" 982 depends on CFI 983 help 984 When selected, Control Flow Integrity (CFI) violations result in a 985 warning instead of a kernel panic. This option should only be used 986 for finding indirect call type mismatches during development. 987 988 If unsure, say N. 989 990config HAVE_ARCH_WITHIN_STACK_FRAMES 991 bool 992 help 993 An architecture should select this if it can walk the kernel stack 994 frames to determine if an object is part of either the arguments 995 or local variables (i.e. that it excludes saved return addresses, 996 and similar) by implementing an inline arch_within_stack_frames(), 997 which is used by CONFIG_HARDENED_USERCOPY. 998 999config HAVE_CONTEXT_TRACKING_USER 1000 bool 1001 help 1002 Provide kernel/user boundaries probes necessary for subsystems 1003 that need it, such as userspace RCU extended quiescent state. 1004 Syscalls need to be wrapped inside user_exit()-user_enter(), either 1005 optimized behind static key or through the slow path using TIF_NOHZ 1006 flag. Exceptions handlers must be wrapped as well. Irqs are already 1007 protected inside ct_irq_enter/ct_irq_exit() but preemption or signal 1008 handling on irq exit still need to be protected. 1009 1010config HAVE_CONTEXT_TRACKING_USER_OFFSTACK 1011 bool 1012 help 1013 Architecture neither relies on exception_enter()/exception_exit() 1014 nor on schedule_user(). Also preempt_schedule_notrace() and 1015 preempt_schedule_irq() can't be called in a preemptible section 1016 while context tracking is CT_STATE_USER. This feature reflects a sane 1017 entry implementation where the following requirements are met on 1018 critical entry code, ie: before user_exit() or after user_enter(): 1019 1020 - Critical entry code isn't preemptible (or better yet: 1021 not interruptible). 1022 - No use of RCU read side critical sections, unless ct_nmi_enter() 1023 got called. 1024 - No use of instrumentation, unless instrumentation_begin() got 1025 called. 1026 1027config HAVE_TIF_NOHZ 1028 bool 1029 help 1030 Arch relies on TIF_NOHZ and syscall slow path to implement context 1031 tracking calls to user_enter()/user_exit(). 1032 1033config HAVE_VIRT_CPU_ACCOUNTING 1034 bool 1035 1036config HAVE_VIRT_CPU_ACCOUNTING_IDLE 1037 bool 1038 help 1039 Architecture has its own way to account idle CPU time and therefore 1040 doesn't implement vtime_account_idle(). 1041 1042config ARCH_HAS_SCALED_CPUTIME 1043 bool 1044 1045config HAVE_VIRT_CPU_ACCOUNTING_GEN 1046 bool 1047 default y if 64BIT 1048 help 1049 With VIRT_CPU_ACCOUNTING_GEN, cputime_t becomes 64-bit. 1050 Before enabling this option, arch code must be audited 1051 to ensure there are no races in concurrent read/write of 1052 cputime_t. For example, reading/writing 64-bit cputime_t on 1053 some 32-bit arches may require multiple accesses, so proper 1054 locking is needed to protect against concurrent accesses. 1055 1056config HAVE_IRQ_TIME_ACCOUNTING 1057 bool 1058 help 1059 Archs need to ensure they use a high enough resolution clock to 1060 support irq time accounting and then call enable_sched_clock_irqtime(). 1061 1062config HAVE_MOVE_PUD 1063 bool 1064 help 1065 Architectures that select this are able to move page tables at the 1066 PUD level. If there are only 3 page table levels, the move effectively 1067 happens at the PGD level. 1068 1069config HAVE_MOVE_PMD 1070 bool 1071 help 1072 Archs that select this are able to move page tables at the PMD level. 1073 1074config HAVE_ARCH_TRANSPARENT_HUGEPAGE 1075 bool 1076 1077config HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD 1078 bool 1079 1080config HAVE_ARCH_HUGE_VMAP 1081 bool 1082 1083# 1084# Archs that select this would be capable of PMD-sized vmaps (i.e., 1085# arch_vmap_pmd_supported() returns true). The VM_ALLOW_HUGE_VMAP flag 1086# must be used to enable allocations to use hugepages. 1087# 1088config HAVE_ARCH_HUGE_VMALLOC 1089 depends on HAVE_ARCH_HUGE_VMAP 1090 bool 1091 1092config ARCH_WANT_HUGE_PMD_SHARE 1093 bool 1094 1095# Archs that want to use pmd_mkwrite on kernel memory need it defined even 1096# if there are no userspace memory management features that use it 1097config ARCH_WANT_KERNEL_PMD_MKWRITE 1098 bool 1099 1100config ARCH_WANT_PMD_MKWRITE 1101 def_bool TRANSPARENT_HUGEPAGE || ARCH_WANT_KERNEL_PMD_MKWRITE 1102 1103config HAVE_ARCH_SOFT_DIRTY 1104 bool 1105 1106config HAVE_MOD_ARCH_SPECIFIC 1107 bool 1108 help 1109 The arch uses struct mod_arch_specific to store data. Many arches 1110 just need a simple module loader without arch specific data - those 1111 should not enable this. 1112 1113config MODULES_USE_ELF_RELA 1114 bool 1115 help 1116 Modules only use ELF RELA relocations. Modules with ELF REL 1117 relocations will give an error. 1118 1119config MODULES_USE_ELF_REL 1120 bool 1121 help 1122 Modules only use ELF REL relocations. Modules with ELF RELA 1123 relocations will give an error. 1124 1125config ARCH_WANTS_MODULES_DATA_IN_VMALLOC 1126 bool 1127 help 1128 For architectures like powerpc/32 which have constraints on module 1129 allocation and need to allocate module data outside of module area. 1130 1131config ARCH_WANTS_EXECMEM_LATE 1132 bool 1133 help 1134 For architectures that do not allocate executable memory early on 1135 boot, but rather require its initialization late when there is 1136 enough entropy for module space randomization, for instance 1137 arm64. 1138 1139config ARCH_HAS_EXECMEM_ROX 1140 bool 1141 depends on MMU && !HIGHMEM 1142 help 1143 For architectures that support allocations of executable memory 1144 with read-only execute permissions. Architecture must implement 1145 execmem_fill_trapping_insns() callback to enable this. 1146 1147config HAVE_IRQ_EXIT_ON_IRQ_STACK 1148 bool 1149 help 1150 Architecture doesn't only execute the irq handler on the irq stack 1151 but also irq_exit(). This way we can process softirqs on this irq 1152 stack instead of switching to a new one when we call __do_softirq() 1153 in the end of an hardirq. 1154 This spares a stack switch and improves cache usage on softirq 1155 processing. 1156 1157config HAVE_SOFTIRQ_ON_OWN_STACK 1158 bool 1159 help 1160 Architecture provides a function to run __do_softirq() on a 1161 separate stack. 1162 1163config SOFTIRQ_ON_OWN_STACK 1164 def_bool HAVE_SOFTIRQ_ON_OWN_STACK && !PREEMPT_RT 1165 1166config ALTERNATE_USER_ADDRESS_SPACE 1167 bool 1168 help 1169 Architectures set this when the CPU uses separate address 1170 spaces for kernel and user space pointers. In this case, the 1171 access_ok() check on a __user pointer is skipped. 1172 1173config PGTABLE_LEVELS 1174 int 1175 default 2 1176 1177config ARCH_HAS_ELF_RANDOMIZE 1178 bool 1179 help 1180 An architecture supports choosing randomized locations for 1181 stack, mmap, brk, and ET_DYN. Defined functions: 1182 - arch_mmap_rnd() 1183 - arch_randomize_brk() 1184 1185config HAVE_ARCH_MMAP_RND_BITS 1186 bool 1187 help 1188 An arch should select this symbol if it supports setting a variable 1189 number of bits for use in establishing the base address for mmap 1190 allocations, has MMU enabled and provides values for both: 1191 - ARCH_MMAP_RND_BITS_MIN 1192 - ARCH_MMAP_RND_BITS_MAX 1193 1194config HAVE_EXIT_THREAD 1195 bool 1196 help 1197 An architecture implements exit_thread. 1198 1199config ARCH_MMAP_RND_BITS_MIN 1200 int 1201 1202config ARCH_MMAP_RND_BITS_MAX 1203 int 1204 1205config ARCH_MMAP_RND_BITS_DEFAULT 1206 int 1207 1208config ARCH_MMAP_RND_BITS 1209 int "Number of bits to use for ASLR of mmap base address" if EXPERT 1210 range ARCH_MMAP_RND_BITS_MIN ARCH_MMAP_RND_BITS_MAX 1211 default ARCH_MMAP_RND_BITS_DEFAULT if ARCH_MMAP_RND_BITS_DEFAULT 1212 default ARCH_MMAP_RND_BITS_MIN 1213 depends on HAVE_ARCH_MMAP_RND_BITS 1214 help 1215 This value can be used to select the number of bits to use to 1216 determine the random offset to the base address of vma regions 1217 resulting from mmap allocations. This value will be bounded 1218 by the architecture's minimum and maximum supported values. 1219 1220 This value can be changed after boot using the 1221 /proc/sys/vm/mmap_rnd_bits tunable 1222 1223config HAVE_ARCH_MMAP_RND_COMPAT_BITS 1224 bool 1225 help 1226 An arch should select this symbol if it supports running applications 1227 in compatibility mode, supports setting a variable number of bits for 1228 use in establishing the base address for mmap allocations, has MMU 1229 enabled and provides values for both: 1230 - ARCH_MMAP_RND_COMPAT_BITS_MIN 1231 - ARCH_MMAP_RND_COMPAT_BITS_MAX 1232 1233config ARCH_MMAP_RND_COMPAT_BITS_MIN 1234 int 1235 1236config ARCH_MMAP_RND_COMPAT_BITS_MAX 1237 int 1238 1239config ARCH_MMAP_RND_COMPAT_BITS_DEFAULT 1240 int 1241 1242config ARCH_MMAP_RND_COMPAT_BITS 1243 int "Number of bits to use for ASLR of mmap base address for compatible applications" if EXPERT 1244 range ARCH_MMAP_RND_COMPAT_BITS_MIN ARCH_MMAP_RND_COMPAT_BITS_MAX 1245 default ARCH_MMAP_RND_COMPAT_BITS_DEFAULT if ARCH_MMAP_RND_COMPAT_BITS_DEFAULT 1246 default ARCH_MMAP_RND_COMPAT_BITS_MIN 1247 depends on HAVE_ARCH_MMAP_RND_COMPAT_BITS 1248 help 1249 This value can be used to select the number of bits to use to 1250 determine the random offset to the base address of vma regions 1251 resulting from mmap allocations for compatible applications This 1252 value will be bounded by the architecture's minimum and maximum 1253 supported values. 1254 1255 This value can be changed after boot using the 1256 /proc/sys/vm/mmap_rnd_compat_bits tunable 1257 1258config HAVE_ARCH_COMPAT_MMAP_BASES 1259 bool 1260 help 1261 This allows 64bit applications to invoke 32-bit mmap() syscall 1262 and vice-versa 32-bit applications to call 64-bit mmap(). 1263 Required for applications doing different bitness syscalls. 1264 1265config HAVE_PAGE_SIZE_4KB 1266 bool 1267 1268config HAVE_PAGE_SIZE_8KB 1269 bool 1270 1271config HAVE_PAGE_SIZE_16KB 1272 bool 1273 1274config HAVE_PAGE_SIZE_32KB 1275 bool 1276 1277config HAVE_PAGE_SIZE_64KB 1278 bool 1279 1280config HAVE_PAGE_SIZE_256KB 1281 bool 1282 1283choice 1284 prompt "MMU page size" 1285 1286config PAGE_SIZE_4KB 1287 bool "4KiB pages" 1288 depends on HAVE_PAGE_SIZE_4KB 1289 help 1290 This option select the standard 4KiB Linux page size and the only 1291 available option on many architectures. Using 4KiB page size will 1292 minimize memory consumption and is therefore recommended for low 1293 memory systems. 1294 Some software that is written for x86 systems makes incorrect 1295 assumptions about the page size and only runs on 4KiB pages. 1296 1297config PAGE_SIZE_8KB 1298 bool "8KiB pages" 1299 depends on HAVE_PAGE_SIZE_8KB 1300 help 1301 This option is the only supported page size on a few older 1302 processors, and can be slightly faster than 4KiB pages. 1303 1304config PAGE_SIZE_16KB 1305 bool "16KiB pages" 1306 depends on HAVE_PAGE_SIZE_16KB 1307 help 1308 This option is usually a good compromise between memory 1309 consumption and performance for typical desktop and server 1310 workloads, often saving a level of page table lookups compared 1311 to 4KB pages as well as reducing TLB pressure and overhead of 1312 per-page operations in the kernel at the expense of a larger 1313 page cache. 1314 1315config PAGE_SIZE_32KB 1316 bool "32KiB pages" 1317 depends on HAVE_PAGE_SIZE_32KB 1318 help 1319 Using 32KiB page size will result in slightly higher performance 1320 kernel at the price of higher memory consumption compared to 1321 16KiB pages. This option is available only on cnMIPS cores. 1322 Note that you will need a suitable Linux distribution to 1323 support this. 1324 1325config PAGE_SIZE_64KB 1326 bool "64KiB pages" 1327 depends on HAVE_PAGE_SIZE_64KB 1328 help 1329 Using 64KiB page size will result in slightly higher performance 1330 kernel at the price of much higher memory consumption compared to 1331 4KiB or 16KiB pages. 1332 This is not suitable for general-purpose workloads but the 1333 better performance may be worth the cost for certain types of 1334 supercomputing or database applications that work mostly with 1335 large in-memory data rather than small files. 1336 1337config PAGE_SIZE_256KB 1338 bool "256KiB pages" 1339 depends on HAVE_PAGE_SIZE_256KB 1340 help 1341 256KiB pages have little practical value due to their extreme 1342 memory usage. The kernel will only be able to run applications 1343 that have been compiled with '-zmax-page-size' set to 256KiB 1344 (the default is 64KiB or 4KiB on most architectures). 1345 1346endchoice 1347 1348config PAGE_SIZE_LESS_THAN_64KB 1349 def_bool y 1350 depends on !PAGE_SIZE_64KB 1351 depends on PAGE_SIZE_LESS_THAN_256KB 1352 1353config PAGE_SIZE_LESS_THAN_256KB 1354 def_bool y 1355 depends on !PAGE_SIZE_256KB 1356 1357config PAGE_SHIFT 1358 int 1359 default 12 if PAGE_SIZE_4KB 1360 default 13 if PAGE_SIZE_8KB 1361 default 14 if PAGE_SIZE_16KB 1362 default 15 if PAGE_SIZE_32KB 1363 default 16 if PAGE_SIZE_64KB 1364 default 18 if PAGE_SIZE_256KB 1365 1366# This allows to use a set of generic functions to determine mmap base 1367# address by giving priority to top-down scheme only if the process 1368# is not in legacy mode (compat task, unlimited stack size or 1369# sysctl_legacy_va_layout). 1370# Architecture that selects this option can provide its own version of: 1371# - STACK_RND_MASK 1372config ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT 1373 bool 1374 depends on MMU 1375 select ARCH_HAS_ELF_RANDOMIZE 1376 1377config HAVE_OBJTOOL 1378 bool 1379 1380config HAVE_JUMP_LABEL_HACK 1381 bool 1382 1383config HAVE_NOINSTR_HACK 1384 bool 1385 1386config HAVE_NOINSTR_VALIDATION 1387 bool 1388 1389config HAVE_UACCESS_VALIDATION 1390 bool 1391 select OBJTOOL 1392 1393config HAVE_STACK_VALIDATION 1394 bool 1395 help 1396 Architecture supports objtool compile-time frame pointer rule 1397 validation. 1398 1399config HAVE_RELIABLE_STACKTRACE 1400 bool 1401 help 1402 Architecture has either save_stack_trace_tsk_reliable() or 1403 arch_stack_walk_reliable() function which only returns a stack trace 1404 if it can guarantee the trace is reliable. 1405 1406config HAVE_ARCH_HASH 1407 bool 1408 default n 1409 help 1410 If this is set, the architecture provides an <asm/hash.h> 1411 file which provides platform-specific implementations of some 1412 functions in <linux/hash.h> or fs/namei.c. 1413 1414config HAVE_ARCH_NVRAM_OPS 1415 bool 1416 1417config ISA_BUS_API 1418 def_bool ISA 1419 1420# 1421# ABI hall of shame 1422# 1423config CLONE_BACKWARDS 1424 bool 1425 help 1426 Architecture has tls passed as the 4th argument of clone(2), 1427 not the 5th one. 1428 1429config CLONE_BACKWARDS2 1430 bool 1431 help 1432 Architecture has the first two arguments of clone(2) swapped. 1433 1434config CLONE_BACKWARDS3 1435 bool 1436 help 1437 Architecture has tls passed as the 3rd argument of clone(2), 1438 not the 5th one. 1439 1440config ODD_RT_SIGACTION 1441 bool 1442 help 1443 Architecture has unusual rt_sigaction(2) arguments 1444 1445config OLD_SIGSUSPEND 1446 bool 1447 help 1448 Architecture has old sigsuspend(2) syscall, of one-argument variety 1449 1450config OLD_SIGSUSPEND3 1451 bool 1452 help 1453 Even weirder antique ABI - three-argument sigsuspend(2) 1454 1455config OLD_SIGACTION 1456 bool 1457 help 1458 Architecture has old sigaction(2) syscall. Nope, not the same 1459 as OLD_SIGSUSPEND | OLD_SIGSUSPEND3 - alpha has sigsuspend(2), 1460 but fairly different variant of sigaction(2), thanks to OSF/1 1461 compatibility... 1462 1463config COMPAT_OLD_SIGACTION 1464 bool 1465 1466config COMPAT_32BIT_TIME 1467 bool "Provide system calls for 32-bit time_t" 1468 default !64BIT || COMPAT 1469 help 1470 This enables 32 bit time_t support in addition to 64 bit time_t support. 1471 This is relevant on all 32-bit architectures, and 64-bit architectures 1472 as part of compat syscall handling. 1473 1474config ARCH_NO_PREEMPT 1475 bool 1476 1477config ARCH_SUPPORTS_RT 1478 bool 1479 1480config CPU_NO_EFFICIENT_FFS 1481 def_bool n 1482 1483config HAVE_ARCH_VMAP_STACK 1484 def_bool n 1485 help 1486 An arch should select this symbol if it can support kernel stacks 1487 in vmalloc space. This means: 1488 1489 - vmalloc space must be large enough to hold many kernel stacks. 1490 This may rule out many 32-bit architectures. 1491 1492 - Stacks in vmalloc space need to work reliably. For example, if 1493 vmap page tables are created on demand, either this mechanism 1494 needs to work while the stack points to a virtual address with 1495 unpopulated page tables or arch code (switch_to() and switch_mm(), 1496 most likely) needs to ensure that the stack's page table entries 1497 are populated before running on a possibly unpopulated stack. 1498 1499 - If the stack overflows into a guard page, something reasonable 1500 should happen. The definition of "reasonable" is flexible, but 1501 instantly rebooting without logging anything would be unfriendly. 1502 1503config VMAP_STACK 1504 default y 1505 bool "Use a virtually-mapped stack" 1506 depends on HAVE_ARCH_VMAP_STACK 1507 depends on !KASAN || KASAN_HW_TAGS || KASAN_VMALLOC 1508 help 1509 Enable this if you want the use virtually-mapped kernel stacks 1510 with guard pages. This causes kernel stack overflows to be 1511 caught immediately rather than causing difficult-to-diagnose 1512 corruption. 1513 1514 To use this with software KASAN modes, the architecture must support 1515 backing virtual mappings with real shadow memory, and KASAN_VMALLOC 1516 must be enabled. 1517 1518config HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET 1519 def_bool n 1520 help 1521 An arch should select this symbol if it can support kernel stack 1522 offset randomization with calls to add_random_kstack_offset() 1523 during syscall entry and choose_random_kstack_offset() during 1524 syscall exit. Careful removal of -fstack-protector-strong and 1525 -fstack-protector should also be applied to the entry code and 1526 closely examined, as the artificial stack bump looks like an array 1527 to the compiler, so it will attempt to add canary checks regardless 1528 of the static branch state. 1529 1530config RANDOMIZE_KSTACK_OFFSET 1531 bool "Support for randomizing kernel stack offset on syscall entry" if EXPERT 1532 default y 1533 depends on HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET 1534 help 1535 The kernel stack offset can be randomized (after pt_regs) by 1536 roughly 5 bits of entropy, frustrating memory corruption 1537 attacks that depend on stack address determinism or 1538 cross-syscall address exposures. 1539 1540 The feature is controlled via the "randomize_kstack_offset=on/off" 1541 kernel boot param, and if turned off has zero overhead due to its use 1542 of static branches (see JUMP_LABEL). 1543 1544 If unsure, say Y. 1545 1546config RANDOMIZE_KSTACK_OFFSET_DEFAULT 1547 bool "Default state of kernel stack offset randomization" 1548 depends on RANDOMIZE_KSTACK_OFFSET 1549 help 1550 Kernel stack offset randomization is controlled by kernel boot param 1551 "randomize_kstack_offset=on/off", and this config chooses the default 1552 boot state. 1553 1554config ARCH_OPTIONAL_KERNEL_RWX 1555 def_bool n 1556 1557config ARCH_OPTIONAL_KERNEL_RWX_DEFAULT 1558 def_bool n 1559 1560config ARCH_HAS_STRICT_KERNEL_RWX 1561 def_bool n 1562 1563config STRICT_KERNEL_RWX 1564 bool "Make kernel text and rodata read-only" if ARCH_OPTIONAL_KERNEL_RWX 1565 depends on ARCH_HAS_STRICT_KERNEL_RWX 1566 default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT 1567 help 1568 If this is set, kernel text and rodata memory will be made read-only, 1569 and non-text memory will be made non-executable. This provides 1570 protection against certain security exploits (e.g. executing the heap 1571 or modifying text) 1572 1573 These features are considered standard security practice these days. 1574 You should say Y here in almost all cases. 1575 1576config ARCH_HAS_STRICT_MODULE_RWX 1577 def_bool n 1578 1579config STRICT_MODULE_RWX 1580 bool "Set loadable kernel module data as NX and text as RO" if ARCH_OPTIONAL_KERNEL_RWX 1581 depends on ARCH_HAS_STRICT_MODULE_RWX && MODULES 1582 default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT 1583 help 1584 If this is set, module text and rodata memory will be made read-only, 1585 and non-text memory will be made non-executable. This provides 1586 protection against certain security exploits (e.g. writing to text) 1587 1588# select if the architecture provides an asm/dma-direct.h header 1589config ARCH_HAS_PHYS_TO_DMA 1590 bool 1591 1592config ARCH_HAS_CPU_RESCTRL 1593 bool 1594 help 1595 An architecture selects this option to indicate that the necessary 1596 hooks are provided to support the common memory system usage 1597 monitoring and control interfaces provided by the 'resctrl' 1598 filesystem (see RESCTRL_FS). 1599 1600config HAVE_ARCH_COMPILER_H 1601 bool 1602 help 1603 An architecture can select this if it provides an 1604 asm/compiler.h header that should be included after 1605 linux/compiler-*.h in order to override macro definitions that those 1606 headers generally provide. 1607 1608config HAVE_ARCH_LIBGCC_H 1609 bool 1610 help 1611 An architecture can select this if it provides an 1612 asm/libgcc.h header that should be included after 1613 linux/libgcc.h in order to override macro definitions that 1614 header generally provides. 1615 1616config HAVE_ARCH_PREL32_RELOCATIONS 1617 bool 1618 help 1619 May be selected by an architecture if it supports place-relative 1620 32-bit relocations, both in the toolchain and in the module loader, 1621 in which case relative references can be used in special sections 1622 for PCI fixup, initcalls etc which are only half the size on 64 bit 1623 architectures, and don't require runtime relocation on relocatable 1624 kernels. 1625 1626config ARCH_USE_MEMREMAP_PROT 1627 bool 1628 1629config LOCK_EVENT_COUNTS 1630 bool "Locking event counts collection" 1631 depends on DEBUG_FS 1632 help 1633 Enable light-weight counting of various locking related events 1634 in the system with minimal performance impact. This reduces 1635 the chance of application behavior change because of timing 1636 differences. The counts are reported via debugfs. 1637 1638# Select if the architecture has support for applying RELR relocations. 1639config ARCH_HAS_RELR 1640 bool 1641 1642config RELR 1643 bool "Use RELR relocation packing" 1644 depends on ARCH_HAS_RELR && TOOLS_SUPPORT_RELR 1645 default y 1646 help 1647 Store the kernel's dynamic relocations in the RELR relocation packing 1648 format. Requires a compatible linker (LLD supports this feature), as 1649 well as compatible NM and OBJCOPY utilities (llvm-nm and llvm-objcopy 1650 are compatible). 1651 1652config ARCH_HAS_MEM_ENCRYPT 1653 bool 1654 1655config ARCH_HAS_CC_PLATFORM 1656 bool 1657 1658config HAVE_SPARSE_SYSCALL_NR 1659 bool 1660 help 1661 An architecture should select this if its syscall numbering is sparse 1662 to save space. For example, MIPS architecture has a syscall array with 1663 entries at 4000, 5000 and 6000 locations. This option turns on syscall 1664 related optimizations for a given architecture. 1665 1666config ARCH_HAS_VDSO_ARCH_DATA 1667 depends on HAVE_GENERIC_VDSO 1668 bool 1669 1670config ARCH_HAS_VDSO_TIME_DATA 1671 bool 1672 1673config HAVE_STATIC_CALL 1674 bool 1675 1676config HAVE_STATIC_CALL_INLINE 1677 bool 1678 depends on HAVE_STATIC_CALL 1679 select OBJTOOL 1680 1681config HAVE_PREEMPT_DYNAMIC 1682 bool 1683 1684config HAVE_PREEMPT_DYNAMIC_CALL 1685 bool 1686 depends on HAVE_STATIC_CALL 1687 select HAVE_PREEMPT_DYNAMIC 1688 help 1689 An architecture should select this if it can handle the preemption 1690 model being selected at boot time using static calls. 1691 1692 Where an architecture selects HAVE_STATIC_CALL_INLINE, any call to a 1693 preemption function will be patched directly. 1694 1695 Where an architecture does not select HAVE_STATIC_CALL_INLINE, any 1696 call to a preemption function will go through a trampoline, and the 1697 trampoline will be patched. 1698 1699 It is strongly advised to support inline static call to avoid any 1700 overhead. 1701 1702config HAVE_PREEMPT_DYNAMIC_KEY 1703 bool 1704 depends on HAVE_ARCH_JUMP_LABEL 1705 select HAVE_PREEMPT_DYNAMIC 1706 help 1707 An architecture should select this if it can handle the preemption 1708 model being selected at boot time using static keys. 1709 1710 Each preemption function will be given an early return based on a 1711 static key. This should have slightly lower overhead than non-inline 1712 static calls, as this effectively inlines each trampoline into the 1713 start of its callee. This may avoid redundant work, and may 1714 integrate better with CFI schemes. 1715 1716 This will have greater overhead than using inline static calls as 1717 the call to the preemption function cannot be entirely elided. 1718 1719config ARCH_WANT_LD_ORPHAN_WARN 1720 bool 1721 help 1722 An arch should select this symbol once all linker sections are explicitly 1723 included, size-asserted, or discarded in the linker scripts. This is 1724 important because we never want expected sections to be placed heuristically 1725 by the linker, since the locations of such sections can change between linker 1726 versions. 1727 1728config HAVE_ARCH_PFN_VALID 1729 bool 1730 1731config ARCH_SUPPORTS_DEBUG_PAGEALLOC 1732 bool 1733 1734config ARCH_SUPPORTS_PAGE_TABLE_CHECK 1735 bool 1736 1737config ARCH_SPLIT_ARG64 1738 bool 1739 help 1740 If a 32-bit architecture requires 64-bit arguments to be split into 1741 pairs of 32-bit arguments, select this option. 1742 1743config ARCH_HAS_ELFCORE_COMPAT 1744 bool 1745 1746config ARCH_HAS_PARANOID_L1D_FLUSH 1747 bool 1748 1749config ARCH_HAVE_TRACE_MMIO_ACCESS 1750 bool 1751 1752config DYNAMIC_SIGFRAME 1753 bool 1754 1755# Select, if arch has a named attribute group bound to NUMA device nodes. 1756config HAVE_ARCH_NODE_DEV_GROUP 1757 bool 1758 1759config ARCH_HAS_HW_PTE_YOUNG 1760 bool 1761 help 1762 Architectures that select this option are capable of setting the 1763 accessed bit in PTE entries when using them as part of linear address 1764 translations. Architectures that require runtime check should select 1765 this option and override arch_has_hw_pte_young(). 1766 1767config ARCH_HAS_NONLEAF_PMD_YOUNG 1768 bool 1769 help 1770 Architectures that select this option are capable of setting the 1771 accessed bit in non-leaf PMD entries when using them as part of linear 1772 address translations. Page table walkers that clear the accessed bit 1773 may use this capability to reduce their search space. 1774 1775config ARCH_HAS_KERNEL_FPU_SUPPORT 1776 bool 1777 help 1778 Architectures that select this option can run floating-point code in 1779 the kernel, as described in Documentation/core-api/floating-point.rst. 1780 1781config ARCH_VMLINUX_NEEDS_RELOCS 1782 bool 1783 help 1784 Whether the architecture needs vmlinux to be built with static 1785 relocations preserved. This is used by some architectures to 1786 construct bespoke relocation tables for KASLR. 1787 1788# Select if architecture uses the common generic TIF bits 1789config HAVE_GENERIC_TIF_BITS 1790 bool 1791 1792source "kernel/gcov/Kconfig" 1793 1794source "scripts/gcc-plugins/Kconfig" 1795 1796config FUNCTION_ALIGNMENT_4B 1797 bool 1798 1799config FUNCTION_ALIGNMENT_8B 1800 bool 1801 1802config FUNCTION_ALIGNMENT_16B 1803 bool 1804 1805config FUNCTION_ALIGNMENT_32B 1806 bool 1807 1808config FUNCTION_ALIGNMENT_64B 1809 bool 1810 1811config FUNCTION_ALIGNMENT 1812 int 1813 default 64 if FUNCTION_ALIGNMENT_64B 1814 default 32 if FUNCTION_ALIGNMENT_32B 1815 default 16 if FUNCTION_ALIGNMENT_16B 1816 default 8 if FUNCTION_ALIGNMENT_8B 1817 default 4 if FUNCTION_ALIGNMENT_4B 1818 default 0 1819 1820config CC_HAS_MIN_FUNCTION_ALIGNMENT 1821 # Detect availability of the GCC option -fmin-function-alignment which 1822 # guarantees minimal alignment for all functions, unlike 1823 # -falign-functions which the compiler ignores for cold functions. 1824 def_bool $(cc-option, -fmin-function-alignment=8) 1825 1826config CC_HAS_SANE_FUNCTION_ALIGNMENT 1827 # Set if the guaranteed alignment with -fmin-function-alignment is 1828 # available or extra care is required in the kernel. Clang provides 1829 # strict alignment always, even with -falign-functions. 1830 def_bool CC_HAS_MIN_FUNCTION_ALIGNMENT || CC_IS_CLANG 1831 1832config ARCH_NEED_CMPXCHG_1_EMU 1833 bool 1834 1835config ARCH_WANTS_PRE_LINK_VMLINUX 1836 bool 1837 help 1838 An architecture can select this if it provides arch/<arch>/tools/Makefile 1839 with .arch.vmlinux.o target to be linked into vmlinux. 1840 1841config ARCH_HAS_CPU_ATTACK_VECTORS 1842 bool 1843 1844endmenu