linux-kernel - [PATCH 1/3] sh/boot: Add static stack-protector to pre-kernel

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Date:   Mon,  2 Oct 2017 12:20:05 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Kees Cook <keescook@...omium.org>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>, linux-sh@...r.kernel.org,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Michal Marek <mmarek@...e.com>, Ingo Molnar <mingo@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Nicholas Piggin <npiggin@...il.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Laura Abbott <labbott@...hat.com>,
        linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-hardening@...ts.openwall.com
Subject: [PATCH 1/3] sh/boot: Add static stack-protector to pre-kernel

The sh decompressor code triggers stack-protector code generation when
using CONFIG_CC_STACKPROTECTOR_STRONG. As done for arm and mips, add a
simple static stack-protector canary. As this wasn't protected before, the
risk of using a weak canary is minimized. Once the kernel is actually up,
a better canary is chosen.

Cc: Yoshinori Sato <ysato@...rs.sourceforge.jp>
Cc: Rich Felker <dalias@...c.org>
Cc: linux-sh@...r.kernel.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 arch/sh/boot/compressed/misc.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/arch/sh/boot/compressed/misc.c b/arch/sh/boot/compressed/misc.c
index ae1dfdb0013b..f4bdc5d00c04 100644
--- a/arch/sh/boot/compressed/misc.c
+++ b/arch/sh/boot/compressed/misc.c
@@ -103,6 +103,18 @@ static void error(char *x)
 	while(1);	/* Halt */
 }
 
+unsigned long __stack_chk_guard;
+
+void __stack_chk_guard_setup(void)
+{
+	__stack_chk_guard = 0x000a0dff;
+}
+
+void __stack_chk_fail(void)
+{
+	error("stack-protector: Kernel stack is corrupted\n");
+}
+
 #ifdef CONFIG_SUPERH64
 #define stackalign	8
 #else
@@ -117,6 +129,8 @@ void decompress_kernel(void)
 {
 	unsigned long output_addr;
 
+	__stack_chk_guard_setup();
+
 #ifdef CONFIG_SUPERH64
 	output_addr = (CONFIG_MEMORY_START + 0x2000);
 #else
-- 
2.7.4