linux-kernel - [PATCH 4/5] arm64: ascii armor the arm64 boot init stack canary

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Date:   Wed, 24 May 2017 11:57:50 -0400
From:   riel@...hat.com
To:     linux-kernel@...r.kernel.org
Cc:     danielmicay@...il.com, tytso@....edu, keescook@...omium.org,
        hpa@...or.com, luto@...capital.net, mingo@...nel.org,
        x86@...nel.org, linux-arm-kernel@...ts.infradead.org,
        catalin.marinas@....com, linux-sh@...r.kernel.org,
        ysato@...rs.sourceforge.jp, kernel-hardening@...ts.openwall.com
Subject: [PATCH 4/5] arm64: ascii armor the arm64 boot init stack canary

From: Rik van Riel <riel@...hat.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 Daniel Micay's linux-hardened tree.

Signed-off-by: Rik van Riel <riel@...hat.com>
---
 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