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authorKees Cook <keescook@chromium.org>2016-05-10 10:55:49 -0700
committerWill Deacon <will.deacon@arm.com>2016-05-11 11:38:10 +0100
commit61462c8a6b140fe2f93cb911684837e05950e680 (patch)
tree250c844648a97cf15d9719244706feae98d75ffc /arch/arm64
parentf228b494e56d949be8d8ea09d4f973d1979201bf (diff)
downloadlinux-61462c8a6b140fe2f93cb911684837e05950e680.tar.bz2
arm64: kernel: Fix incorrect brk randomization
This fixes two issues with the arm64 brk randomziation. First, the STACK_RND_MASK was being used incorrectly. The original code was: unsigned long range_end = base + (STACK_RND_MASK << PAGE_SHIFT) + 1; STACK_RND_MASK is 0x7ff (32-bit) or 0x3ffff (64-bit), with 4K pages where PAGE_SHIFT is 12: #define STACK_RND_MASK (test_thread_flag(TIF_32BIT) ? \ 0x7ff >> (PAGE_SHIFT - 12) : \ 0x3ffff >> (PAGE_SHIFT - 12)) This means the resulting offset from base would be 0x7ff0001 or 0x3ffff0001, which is wrong since it creates an unaligned end address. It was likely intended to be: unsigned long range_end = base + ((STACK_RND_MASK + 1) << PAGE_SHIFT) Which would result in offsets of 0x800000 (32-bit) and 0x40000000 (64-bit). However, even this corrected 32-bit compat offset (0x00800000) is much smaller than native ARM's brk randomization value (0x02000000): unsigned long arch_randomize_brk(struct mm_struct *mm) { unsigned long range_end = mm->brk + 0x02000000; return randomize_range(mm->brk, range_end, 0) ? : mm->brk; } So, instead of basing arm64's brk randomization on mistaken STACK_RND_MASK calculations, just use specific corrected values for compat (0x2000000) and native arm64 (0x40000000). Reviewed-by: Jon Medhurst <tixy@linaro.org> Signed-off-by: Kees Cook <keescook@chromium.org> [will: use is_compat_task() as suggested by tixy] Signed-off-by: Will Deacon <will.deacon@arm.com>
Diffstat (limited to 'arch/arm64')
-rw-r--r--arch/arm64/kernel/process.c15
1 files changed, 8 insertions, 7 deletions
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 80624829db61..ad4a7e132ead 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -382,13 +382,14 @@ unsigned long arch_align_stack(unsigned long sp)
return sp & ~0xf;
}
-static unsigned long randomize_base(unsigned long base)
-{
- unsigned long range_end = base + (STACK_RND_MASK << PAGE_SHIFT) + 1;
- return randomize_range(base, range_end, 0) ? : base;
-}
-
unsigned long arch_randomize_brk(struct mm_struct *mm)
{
- return randomize_base(mm->brk);
+ unsigned long range_end = mm->brk;
+
+ if (is_compat_task())
+ range_end += 0x02000000;
+ else
+ range_end += 0x40000000;
+
+ return randomize_range(mm->brk, range_end, 0) ? : mm->brk;
}