From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965335AbcKOHDr (ORCPT ); Tue, 15 Nov 2016 02:03:47 -0500 Received: from ozlabs.org ([103.22.144.67]:51569 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964963AbcKOHDp (ORCPT ); Tue, 15 Nov 2016 02:03:45 -0500 From: Michael Ellerman To: keescook@chromium.org Cc: linux-kernel@vger.kernel.org Subject: [PATCH] lkdtm: Prevent the compiler from optimising lkdtm_CORRUPT_STACK() Date: Tue, 15 Nov 2016 18:02:32 +1100 Message-Id: <1479193352-486-1-git-send-email-mpe@ellerman.id.au> X-Mailer: git-send-email 2.7.4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org At least on powerpc with GCC 6, the compiler is smart enough to optimise lkdtm_CORRUPT_STACK() into an empty function that just returns. If we print the buffer after we've written to it that prevents the compiler from optimising away data and the memset(). Signed-off-by: Michael Ellerman --- drivers/misc/lkdtm_bugs.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/misc/lkdtm_bugs.c b/drivers/misc/lkdtm_bugs.c index 182ae1894b32..30e62dd7e7ca 100644 --- a/drivers/misc/lkdtm_bugs.c +++ b/drivers/misc/lkdtm_bugs.c @@ -80,7 +80,8 @@ noinline void lkdtm_CORRUPT_STACK(void) /* Use default char array length that triggers stack protection. */ char data[8]; - memset((void *)data, 0, 64); + memset((void *)data, 'a', 64); + pr_info("Corrupted stack with '%16s'...\n", data); } void lkdtm_UNALIGNED_LOAD_STORE_WRITE(void) -- 2.7.4