linux-kernel - [PATCH] misc: lkdtm: Add volatile to intentional NULL pointer reference

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Message-Id: <20170414211509.41940-1-mka@chromium.org>
Date:   Fri, 14 Apr 2017 14:15:09 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kees Cook <keescook@...omium.org>
Cc:     linux-kernel@...r.kernel.org,
        Grant Grundler <grundler@...omium.org>,
        Greg Hackmann <ghackmann@...gle.com>,
        Michael Davidson <md@...gle.com>,
        Matthias Kaehlcke <mka@...omium.org>
Subject: [PATCH] misc: lkdtm: Add volatile to intentional NULL pointer reference

From: Michael Davidson <md@...gle.com>

Add a volatile qualifier where a NULL pointer is deliberately
dereferenced to trigger a panic.

Without the volatile qualifier clang will issue the following warning:
"indirection of non-volatile null pointer will be deleted,
not trap [-Wnull-dereference]" and replace the pointer reference
with a __builtin_trap() (which generates a ud2 instruction on x86_64).

Signed-off-by: Michael Davidson <md@...gle.com>
Signed-off-by: Matthias Kaehlcke <mka@...omium.org>
---
 drivers/misc/lkdtm_bugs.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/misc/lkdtm_bugs.c b/drivers/misc/lkdtm_bugs.c
index e3f4cd8876b5..d734d75afade 100644
--- a/drivers/misc/lkdtm_bugs.c
+++ b/drivers/misc/lkdtm_bugs.c
@@ -67,7 +67,7 @@ void lkdtm_WARNING(void)
 
 void lkdtm_EXCEPTION(void)
 {
-	*((int *) 0) = 0;
+	*((volatile int *) 0) = 0;
 }
 
 void lkdtm_LOOP(void)
-- 
2.12.2.762.g0e3151a226-goog