hardening: Enable KCFI and some other options

Add some stuff that got missed along the way:

- CONFIG_UNWIND_PATCH_PAC_INTO_SCS=y so SCS vs PAC is hardware
selectable.

- CONFIG_X86_KERNEL_IBT=y while a default, just be sure.

- CONFIG_CFI_CLANG=y globally.

- CONFIG_PAGE_TABLE_CHECK=y for userspace mapping sanity.

Reviewed-by: Nathan Chancellor <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Kees Cook <[e-mail]>

arch/arm64/configs/hardening.config

···
 
 # Software Shadow Stack or PAC
 CONFIG_SHADOW_CALL_STACK=y
+CONFIG_UNWIND_PATCH_PAC_INTO_SCS=y
 
 # Pointer authentication (ARMv8.3 and later). If hardware actually supports
 # it, one can turn off CONFIG_STACKPROTECTOR_STRONG with this enabled.

arch/x86/configs/hardening.config

···
 CONFIG_INTEL_IOMMU_SVM=y
 CONFIG_AMD_IOMMU=y
 
+# Enforce CET Indirect Branch Tracking in the kernel.
+CONFIG_X86_KERNEL_IBT=y
+
 # Enable CET Shadow Stack for userspace.
 CONFIG_X86_USER_SHADOW_STACK=y

kernel/configs/hardening.config

···
 CONFIG_SHUFFLE_PAGE_ALLOCATOR=y
 CONFIG_RANDOM_KMALLOC_CACHES=y
 
+# Sanity check userspace page table mappings.
+CONFIG_PAGE_TABLE_CHECK=y
+CONFIG_PAGE_TABLE_CHECK_ENFORCED=y
+
 # Randomize kernel stack offset on syscall entry.
 CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT=y
 
···
 
 # Provides some protections against SYN flooding.
 CONFIG_SYN_COOKIES=y
+
+# Enable Kernel Control Flow Integrity (currently Clang only).
+CONFIG_CFI_CLANG=y
+# CONFIG_CFI_PERMISSIVE is not set
 
 # Attack surface reduction: do not autoload TTY line disciplines.
 # CONFIG_LDISC_AUTOLOAD is not set