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[3/5] x86: ascii armor the x86_64 boot init stack canary

Message ID 20170519212636.30440-4-riel@redhat.com (mailing list archive)
State New, archived
Headers show

Commit Message

Rik van Riel May 19, 2017, 9:26 p.m. UTC 
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(+)
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Patch

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