mm: expose arch_mmap_rnd when available

When an architecture fully supports randomizing the ELF load location,
a per-arch mmap_rnd() function is used to find a randomized mmap base.
In preparation for randomizing the location of ET_DYN binaries
separately from mmap, this renames and exports these functions as
arch_mmap_rnd(). Additionally introduces CONFIG_ARCH_HAS_ELF_RANDOMIZE
for describing this feature on architectures that support it
(which is a superset of ARCH_BINFMT_ELF_RANDOMIZE_PIE, since s390
already supports a separated ET_DYN ASLR from mmap ASLR without the
ARCH_BINFMT_ELF_RANDOMIZE_PIE logic).

Signed-off-by: Kees Cook <[e-mail]>
Cc: Hector Marco-Gisbert <[e-mail]>
Cc: Russell King <[e-mail]>
Reviewed-by: Ingo Molnar <[e-mail]>
Cc: Catalin Marinas <[e-mail]>
Cc: Will Deacon <[e-mail]>
Cc: Ralf Baechle <[e-mail]>
Cc: Benjamin Herrenschmidt <[e-mail]>
Cc: Paul Mackerras <[e-mail]>
Cc: Michael Ellerman <[e-mail]>
Cc: Martin Schwidefsky <[e-mail]>
Cc: Heiko Carstens <[e-mail]>
Cc: Alexander Viro <[e-mail]>
Cc: Oleg Nesterov <[e-mail]>
Cc: Andy Lutomirski <[e-mail]>
Cc: "David A. Long" <[e-mail]>
Cc: Andrey Ryabinin <[e-mail]>
Cc: Arun Chandran <[e-mail]>
Cc: Yann Droneaud <[e-mail]>
Cc: Min-Hua Chen <[e-mail]>
Cc: Paul Burton <[e-mail]>
Cc: Alex Smith <[e-mail]>
Cc: Markos Chandras <[e-mail]>
Cc: Vineeth Vijayan <[e-mail]>
Cc: Jeff Bailey <[e-mail]>
Cc: Michael Holzheu <[e-mail]>
Cc: Ben Hutchings <[e-mail]>
Cc: Behan Webster <[e-mail]>
Cc: Ismael Ripoll <[e-mail]>
Cc: Jan-Simon Mller <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

arch/Kconfig

···
 	int
 	default 2
 
+config ARCH_HAS_ELF_RANDOMIZE
+	bool
+	help
+	  An architecture supports choosing randomized locations for
+	  stack, mmap, brk, and ET_DYN. Defined functions:
+	  - arch_mmap_rnd()
+
 #
 # ABI hall of shame
 #

arch/arm/Kconfig

···
 	default y
 	select ARCH_BINFMT_ELF_RANDOMIZE_PIE
 	select ARCH_HAS_ATOMIC64_DEC_IF_POSITIVE
+	select ARCH_HAS_ELF_RANDOMIZE
 	select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST
 	select ARCH_HAVE_CUSTOM_GPIO_H
 	select ARCH_HAS_GCOV_PROFILE_ALL

arch/arm/mm/mmap.c

···
 	return addr;
 }
 
-static unsigned long mmap_rnd(void)
+unsigned long arch_mmap_rnd(void)
 {
 	unsigned long rnd;
 
···
 	unsigned long random_factor = 0UL;
 
 	if (current->flags & PF_RANDOMIZE)
-		random_factor = mmap_rnd();
+		random_factor = arch_mmap_rnd();
 
 	if (mmap_is_legacy()) {
 		mm->mmap_base = TASK_UNMAPPED_BASE + random_factor;

arch/arm64/Kconfig

···
 	def_bool y
 	select ARCH_BINFMT_ELF_RANDOMIZE_PIE
 	select ARCH_HAS_ATOMIC64_DEC_IF_POSITIVE
+	select ARCH_HAS_ELF_RANDOMIZE
 	select ARCH_HAS_GCOV_PROFILE_ALL
 	select ARCH_HAS_SG_CHAIN
 	select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST

arch/arm64/mm/mmap.c

···
 	return sysctl_legacy_va_layout;
 }
 
-static unsigned long mmap_rnd(void)
+unsigned long arch_mmap_rnd(void)
 {
 	unsigned long rnd;
 
···
 	unsigned long random_factor = 0UL;
 
 	if (current->flags & PF_RANDOMIZE)
-		random_factor = mmap_rnd();
+		random_factor = arch_mmap_rnd();
 
 	/*
 	 * Fall back to the standard layout if the personality bit is set, or

arch/mips/Kconfig

···
 	select HAVE_DEBUG_KMEMLEAK
 	select HAVE_SYSCALL_TRACEPOINTS
 	select ARCH_BINFMT_ELF_RANDOMIZE_PIE
+	select ARCH_HAS_ELF_RANDOMIZE
 	select HAVE_ARCH_TRANSPARENT_HUGEPAGE if CPU_SUPPORTS_HUGEPAGES && 64BIT
 	select RTC_LIB if !MACH_LOONGSON
 	select GENERIC_ATOMIC64 if !64BIT

arch/mips/mm/mmap.c

···
 			addr0, len, pgoff, flags, DOWN);
 }
 
-static unsigned long mmap_rnd(void)
+unsigned long arch_mmap_rnd(void)
 {
 	unsigned long rnd;
 
···
 	unsigned long random_factor = 0UL;
 
 	if (current->flags & PF_RANDOMIZE)
-		random_factor = mmap_rnd();
+		random_factor = arch_mmap_rnd();
 
 	if (mmap_is_legacy()) {
 		mm->mmap_base = TASK_UNMAPPED_BASE + random_factor;

arch/powerpc/Kconfig

···
 	select ARCH_MIGHT_HAVE_PC_SERIO
 	select BINFMT_ELF
 	select ARCH_BINFMT_ELF_RANDOMIZE_PIE
+	select ARCH_HAS_ELF_RANDOMIZE
 	select OF
 	select OF_EARLY_FLATTREE
 	select OF_RESERVED_MEM

arch/powerpc/mm/mmap.c

···
 	return sysctl_legacy_va_layout;
 }
 
-static unsigned long mmap_rnd(void)
+unsigned long arch_mmap_rnd(void)
 {
 	unsigned long rnd;
 
···
 	unsigned long random_factor = 0UL;
 
 	if (current->flags & PF_RANDOMIZE)
-		random_factor = mmap_rnd();
+		random_factor = arch_mmap_rnd();
 
 	/*
 	 * Fall back to the standard layout if the personality

arch/s390/Kconfig

···
 	def_bool y
 	select ARCH_HAS_ATOMIC64_DEC_IF_POSITIVE
 	select ARCH_HAS_DEBUG_STRICT_USER_COPY_CHECKS
+	select ARCH_HAS_ELF_RANDOMIZE
 	select ARCH_HAS_GCOV_PROFILE_ALL
 	select ARCH_HAS_SG_CHAIN
 	select ARCH_HAVE_NMI_SAFE_CMPXCHG

arch/s390/mm/mmap.c

···
 	return sysctl_legacy_va_layout;
 }
 
-static unsigned long mmap_rnd(void)
+unsigned long arch_mmap_rnd(void)
 {
 	if (is_32bit_task())
 		return (get_random_int() & 0x7ff) << PAGE_SHIFT;
···
 		base &= ~((1UL << 32) - 1);
 
 	if (current->flags & PF_RANDOMIZE)
-		base += mmap_rnd();
+		base += arch_mmap_rnd();
 
 	return base;
 }
···
 	unsigned long random_factor = 0UL;
 
 	if (current->flags & PF_RANDOMIZE)
-		random_factor = mmap_rnd();
+		random_factor = arch_mmap_rnd();
 
 	/*
 	 * Fall back to the standard layout if the personality
···
 	unsigned long random_factor = 0UL;
 
 	if (current->flags & PF_RANDOMIZE)
-		random_factor = mmap_rnd();
+		random_factor = arch_mmap_rnd();
 
 	/*
 	 * Fall back to the standard layout if the personality

arch/x86/Kconfig

···
 	select HAVE_ARCH_KASAN if X86_64 && SPARSEMEM_VMEMMAP
 	select HAVE_USER_RETURN_NOTIFIER
 	select ARCH_BINFMT_ELF_RANDOMIZE_PIE
+	select ARCH_HAS_ELF_RANDOMIZE
 	select HAVE_ARCH_JUMP_LABEL
 	select ARCH_HAS_ATOMIC64_DEC_IF_POSITIVE
 	select SPARSE_IRQ

arch/x86/mm/mmap.c

···
 	return sysctl_legacy_va_layout;
 }
 
-static unsigned long mmap_rnd(void)
+unsigned long arch_mmap_rnd(void)
 {
 	unsigned long rnd;
 
···
 	unsigned long random_factor = 0UL;
 
 	if (current->flags & PF_RANDOMIZE)
-		random_factor = mmap_rnd();
+		random_factor = arch_mmap_rnd();
 
 	mm->mmap_legacy_base = mmap_legacy_base(random_factor);
 

include/linux/elf-randomize.h

···
+#ifndef _ELF_RANDOMIZE_H
+#define _ELF_RANDOMIZE_H
+
+#ifndef CONFIG_ARCH_HAS_ELF_RANDOMIZE
+static inline unsigned long arch_mmap_rnd(void) { return 0; }
+#else
+extern unsigned long arch_mmap_rnd(void);
+#endif
+
+#endif