Subject: [PATCH 4/5] arm64: ascii armor the arm64 boot init stack canary

From: [email-masked] (riel at redhat.com)
Date: Fri, 19 May 2017 17:26:35 -0400

From: Rik van Riel <[email-masked]>

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 <[email-masked]>
---
 arch/arm64/include/asm/stackprotector.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm64/include/asm/stackprotector.h b/arch/arm64/include/asm/stackprotector.h
index fe5e287dc56b..b86a0865ddf1 100644
--- a/arch/arm64/include/asm/stackprotector.h
+++ b/arch/arm64/include/asm/stackprotector.h
@@ -30,6 +30,7 @@ static __always_inline void boot_init_stack_canary(void)
 	/* Try to get a semi random initial value. */
 	get_random_bytes(&canary, sizeof(canary));
 	canary ^= LINUX_VERSION_CODE;
+	canary &= CANARY_MASK;
 
 	current->stack_canary = canary;
 	__stack_chk_guard = current->stack_canary;
-- 
2.9.3