linux-kernel - [PATCH 2/6] bug: Improve unlikely() in data corruption check

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Message-Id: <1488827386-87193-3-git-send-email-keescook@chromium.org>
Date:   Mon,  6 Mar 2017 11:09:42 -0800
From:   Kees Cook <keescook@...omium.org>
To:     kernel-hardening@...ts.openwall.com
Cc:     Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Rik van Riel <riel@...hat.com>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Olof Johansson <olof@...om.net>,
        Peter Zijlstra <peterz@...radead.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 2/6] bug: Improve unlikely() in data corruption check

This improves the compiler branch-hinting used in CHECK_DATA_CORRUPTION(),
similar to how it is done in WARN_ON() and friends.

Signed-off-by: Kees Cook <keescook@...omium.org>
---
 include/linux/bug.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/linux/bug.h b/include/linux/bug.h
index 5828489309bb..5ef65dc2ed8b 100644
--- a/include/linux/bug.h
+++ b/include/linux/bug.h
@@ -129,15 +129,15 @@ static inline enum bug_trap_type report_bug(unsigned long bug_addr,
 static inline __must_check bool check_data_corruption(bool v) { return v; }
 #define CHECK_DATA_CORRUPTION(condition, fmt, ...)			 \
 	check_data_corruption(({					 \
-		bool corruption = unlikely(condition);			 \
-		if (corruption) {					 \
+		bool corruption = !!(condition);			 \
+		if (unlikely(corruption)) {				 \
 			if (IS_ENABLED(CONFIG_BUG_ON_DATA_CORRUPTION)) { \
 				pr_err(fmt, ##__VA_ARGS__);		 \
 				BUG();					 \
 			} else						 \
 				WARN(1, fmt, ##__VA_ARGS__);		 \
 		}							 \
-		corruption;						 \
+		unlikely(corruption);					 \
 	}))
 
 #endif	/* _LINUX_BUG_H */
-- 
2.7.4