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arm64: Basic Branch Target Identification support

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This patch adds the bare minimum required to expose the ARMv8.5
Branch Target Identification feature to userspace.

By itself, this does _not_ automatically enable BTI for any initial
executable pages mapped by execve().  This will come later, but for
now it should be possible to enable BTI manually on those pages by
using mprotect() from within the target process.

Other arches already using the generic mman.h are already using
0x10 for arch-specific prot flags, so we use that for PROT_BTI
here.

For consistency, signal handler entry points in BTI guarded pages
are required to be annotated as such, just like any other function.
This blocks a relatively minor attack vector, but comforming
userspace will have the annotations anyway, so we may as well
enforce them.

Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
Dave Martin
2020-03-16 16:50:45 +00:00
committed by Catalin Marinas
parent 00e19ceec8
commit 8ef8f360cf
23 changed files with 172 additions and 4 deletions
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3
include/linux/mm.h
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@@ -324,6 +324,9 @@ extern unsigned int kobjsize(const void *objp);
#elif defined(CONFIG_SPARC64)
# define VM_SPARC_ADI VM_ARCH_1 /* Uses ADI tag for access control */
# define VM_ARCH_CLEAR VM_SPARC_ADI
#elif defined(CONFIG_ARM64)
# define VM_ARM64_BTI VM_ARCH_1 /* BTI guarded page, a.k.a. GP bit */
# define VM_ARCH_CLEAR VM_ARM64_BTI
#elif !defined(CONFIG_MMU)
# define VM_MAPPED_COPY VM_ARCH_1 /* T if mapped copy of data (nommu mmap) */
#endif