From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753408AbbDGJll (ORCPT ); Tue, 7 Apr 2015 05:41:41 -0400 Received: from terminus.zytor.com ([198.137.202.10]:48246 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753376AbbDGJld (ORCPT ); Tue, 7 Apr 2015 05:41:33 -0400 Date: Tue, 7 Apr 2015 02:41:04 -0700 From: tip-bot for Borislav Petkov Message-ID: Cc: torvalds@linux-foundation.org, tglx@linutronix.de, hpa@zytor.com, dvlasenk@redhat.com, luto@amacapital.net, bp@alien8.de, mingo@kernel.org, brgerst@gmail.com, linux-kernel@vger.kernel.org, bp@suse.de Reply-To: bp@suse.de, brgerst@gmail.com, linux-kernel@vger.kernel.org, mingo@kernel.org, bp@alien8.de, luto@amacapital.net, torvalds@linux-foundation.org, dvlasenk@redhat.com, tglx@linutronix.de, hpa@zytor.com In-Reply-To: <1428181662-18020-1-git-send-email-bp@alien8.de> References: <1428181662-18020-1-git-send-email-bp@alien8.de> To: linux-tip-commits@vger.kernel.org Subject: [tip:x86/asm] x86/alternatives: Guard NOPs optimization Git-Commit-ID: 69df353ff305805fc16082d0c5bfa6e20fa8b863 X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 69df353ff305805fc16082d0c5bfa6e20fa8b863 Gitweb: http://git.kernel.org/tip/69df353ff305805fc16082d0c5bfa6e20fa8b863 Author: Borislav Petkov AuthorDate: Sat, 4 Apr 2015 23:07:42 +0200 Committer: Ingo Molnar CommitDate: Mon, 6 Apr 2015 09:24:09 +0200 x86/alternatives: Guard NOPs optimization Take a look at the first instruction byte before optimizing the NOP - there might be something else there already, like the ALTERNATIVE_2() in rdtsc_barrier() which NOPs out on AMD even though we just patched in an MFENCE. This happens because the alternatives sees X86_FEATURE_MFENCE_RDTSC, AMD CPUs set it, we patch in the MFENCE and right afterwards it sees X86_FEATURE_LFENCE_RDTSC which AMD CPUs don't set and we blindly optimize the NOP. Checking whether at least the first byte is 0x90 prevents that. Signed-off-by: Borislav Petkov Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/1428181662-18020-1-git-send-email-bp@alien8.de Signed-off-by: Ingo Molnar --- arch/x86/kernel/alternative.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index 7c4ad00..aef6531 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -325,6 +325,9 @@ done: static void __init_or_module optimize_nops(struct alt_instr *a, u8 *instr) { + if (instr[0] != 0x90) + return; + add_nops(instr + (a->instrlen - a->padlen), a->padlen); DUMP_BYTES(instr, a->instrlen, "%p: [%d:%d) optimized NOPs: ",