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Subject[PATCH 3/5] x86: ascii armor the x86_64 boot init stack canary
Date
From: Rik van Riel <riel@redhat.com>

Use the ascii-armor canary to prevent unterminated C string overflows
from being able to successfully overwrite the canary, even if they
somehow obtain the canary value.

Inspired by execshield ascii-armor and PaX/grsecurity.

Signed-off-by: Rik van Riel <riel@redhat.com>
---
arch/x86/include/asm/stackprotector.h | 1 +
1 file changed, 1 insertion(+)

diff --git a/arch/x86/include/asm/stackprotector.h b/arch/x86/include/asm/stackprotector.h
index dcbd9bcce714..8abedf1d650e 100644
--- a/arch/x86/include/asm/stackprotector.h
+++ b/arch/x86/include/asm/stackprotector.h
@@ -74,6 +74,7 @@ static __always_inline void boot_init_stack_canary(void)
get_random_bytes(&canary, sizeof(canary));
tsc = rdtsc();
canary += tsc + (tsc << 32UL);
+ canary &= CANARY_MASK;

current->stack_canary = canary;
#ifdef CONFIG_X86_64
--
2.9.3
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