From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on gnuweeb.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=5.0 tests=ALL_TRUSTED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,NO_DNS_FOR_FROM,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.6 Received: from integral2.. (unknown [182.2.70.161]) by gnuweeb.org (Postfix) with ESMTPSA id 0076C7E72E; Tue, 29 Mar 2022 10:47:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=gnuweeb.org; s=default; t=1648550843; bh=ZrvJYaZ/dGXaHa3O2COi7cmDKWMxBGfg7zKTtQwreOY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=BYMidkgOUanB8Jk52lhdqv8mYzAyg8q4Ijnp/myJPf7Vgw/ziXMUl85zhC2+7+ztn JsK3WO/cYNkN4jpG4x37opvzFjmOPLZcQFJUXYhZbGfiiWncLAIM9GRmQWOEMnRgLE AYaabsatBt7OPsn3x1D0LNU0G8mT2uOU8kai0gaNCntbCyHksKMfUDvX9rbmOBTfz2 +FHCFVpEUIHEoXxwp3uhYsJbWLc76IRj5nMo/snsUR2VpYINsHKmovy/3zJwjcadbu ISH6A1iT1XDM9DICHKwdYq2Ftj+WJhEXB8NWZcYUxGqf14Nk14g+pmVafuo7OSX72U 0zD/VGonGv9SA== From: Ammar Faizi To: Borislav Petkov , Thomas Gleixner Cc: Ammar Faizi , Alviro Iskandar Setiawan , Dave Hansen , "H. Peter Anvin" , Ingo Molnar , Tony Luck , Yazen Ghannam , Linux Edac Mailing List , Linux Kernel Mailing List , Stable Kernel , GNU/Weeb Mailing List , x86 Mailing List , David Laight , Jiri Hladky Subject: [PATCH v6 1/2] x86/delay: Fix the wrong asm constraint in `delay_loop()` Date: Tue, 29 Mar 2022 17:47:04 +0700 Message-Id: <20220329104705.65256-2-ammarfaizi2@gnuweeb.org> X-Mailer: git-send-email 2.32.0 In-Reply-To: <20220329104705.65256-1-ammarfaizi2@gnuweeb.org> References: <20220329104705.65256-1-ammarfaizi2@gnuweeb.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit List-Id: The asm constraint does not reflect that the asm statement can modify the value of @loops. But the asm statement in delay_loop() does modify the @loops. Specifiying the wrong constraint may lead to undefined behavior, it may clobber random stuff (e.g. local variable, important temporary value in regs, etc.). This is especially dangerous when the compiler decides to inline the function and since it doesn't know that the value gets modified, it might decide to use it from a register directly without reloading it. Fix this by changing the constraint from "a" (as an input) to "+a" (as an input and output). Cc: David Laight Cc: Jiri Hladky Cc: Alviro Iskandar Setiawan Fixes: e01b70ef3eb3 ("x86: fix bug in arch/i386/lib/delay.c file, delay_loop function") Signed-off-by: Ammar Faizi --- v6: - Remove unnecessary Cc tags. - Update commit message, emphasize the danger when the compiler decides to inline the function. - Fix the Fixes tag sha1. - Remove stable Cc. --- arch/x86/lib/delay.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/x86/lib/delay.c b/arch/x86/lib/delay.c index 65d15df6212d..0e65d00e2339 100644 --- a/arch/x86/lib/delay.c +++ b/arch/x86/lib/delay.c @@ -54,8 +54,8 @@ static void delay_loop(u64 __loops) " jnz 2b \n" "3: dec %0 \n" - : /* we don't need output */ - :"a" (loops) + : "+a" (loops) + : ); } -- Ammar Faizi