From: Rik van Riel <riel@redhat.com>
Date: Wed, 12 Jul 2017 21:36:23 +0000 (-0700)
Subject: x86: ascii armor the x86_64 boot init stack canary
X-Git-Tag: v4.14-rc1~476^2~29
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=bf9eb5443844e288b73f7963dfc67a0d2fbc3849;p=platform%2Fkernel%2Flinux-rpi.git

x86: ascii armor the x86_64 boot init stack canary

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.

Link: http://lkml.kernel.org/r/20170524155751.424-4-riel@redhat.com
Signed-off-by: Rik van Riel <riel@redhat.com>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Daniel Micay <danielmicay@gmail.com>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---

diff --git a/arch/x86/include/asm/stackprotector.h b/arch/x86/include/asm/stackprotector.h
index dcbd9bc..8abedf1 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