linux-kernel - [PATCH 1/4] lkdtm: fix stack protector trigger

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Message-Id: <1373302893-4990-1-git-send-email-keescook@chromium.org>
Date:	Mon,  8 Jul 2013 10:01:30 -0700
From:	Kees Cook <keescook@...omium.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Arnd Bergmann <arnd@...db.de>, Ankita Garg <ankita@...ibm.com>,
	Simon Kagstrom <simon.kagstrom@...insight.net>,
	Kees Cook <keescook@...omium.org>
Subject: [PATCH 1/4] lkdtm: fix stack protector trigger

The -fstack-protector compiler flag will only build stack protections if
a character array is seen. Additionally, the offset to the saved
instruction pointer changes based on architecture, so stomp much harder
(64 bytes) when corrupting the stack.

Signed-off-by: Kees Cook <keescook@...omium.org>
---
 drivers/misc/lkdtm.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/misc/lkdtm.c b/drivers/misc/lkdtm.c
index 08aad69..adb6bde 100644
--- a/drivers/misc/lkdtm.c
+++ b/drivers/misc/lkdtm.c
@@ -295,10 +295,10 @@ static void lkdtm_do_action(enum ctype which)
 		(void) recursive_loop(0);
 		break;
 	case CT_CORRUPT_STACK: {
-		volatile u32 data[8];
-		volatile u32 *p = data;
+		/* Make sure the compiler creates and uses an 8 char array. */
+		volatile char data[8];
 
-		p[12] = 0x12345678;
+		memset((void *)data, 0, 64);
 		break;
 	}
 	case CT_UNALIGNED_LOAD_STORE_WRITE: {
-- 
1.7.9.5

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