From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4D9E1C677FC for ; Thu, 11 Oct 2018 15:40:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 024D821477 for ; Thu, 11 Oct 2018 15:40:27 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="rK0oamdX" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 024D821477 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linuxfoundation.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730185AbeJKXII (ORCPT ); Thu, 11 Oct 2018 19:08:08 -0400 Received: from mail.kernel.org ([198.145.29.99]:38274 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726647AbeJKXIH (ORCPT ); Thu, 11 Oct 2018 19:08:07 -0400 Received: from localhost (ip-213-127-77-176.ip.prioritytelecom.net [213.127.77.176]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 92672213A2; Thu, 11 Oct 2018 15:40:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1539272423; bh=MHpZXCPdT0DGLNVV34gttrAsqSInitRf7w4nORNsBZg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=rK0oamdXv9vtLH649YD5WLGzbclUP+gbeLDCPv8NY0enhIYHxeM9aZAJlv6pKEmDr ol/+TfoPcMfkyofG+AvbvWQgpWkMz+HJeOzBVPKqlI/EOTkChLWmdXLkTSOjXzIeoq /AMfAtD9JDmzzLRWE7QYbCtYMrz5ImH7gXehm8/s= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Andy Lutomirski , Thomas Gleixner Subject: [PATCH 3.18 102/120] x86/vdso: Fix asm constraints on vDSO syscall fallbacks Date: Thu, 11 Oct 2018 17:34:43 +0200 Message-Id: <20181011152554.001800946@linuxfoundation.org> X-Mailer: git-send-email 2.19.1 In-Reply-To: <20181011152549.500488630@linuxfoundation.org> References: <20181011152549.500488630@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Andy Lutomirski commit 715bd9d12f84d8f5cc8ad21d888f9bc304a8eb0b upstream. The syscall fallbacks in the vDSO have incorrect asm constraints. They are not marked as writing to their outputs -- instead, they are marked as clobbering "memory", which is useless. In particular, gcc is smart enough to know that the timespec parameter hasn't escaped, so a memory clobber doesn't clobber it. And passing a pointer as an asm *input* does not tell gcc that the pointed-to value is changed. Add in the fact that the asm instructions weren't volatile, and gcc was free to omit them entirely unless their sole output (the return value) is used. Which it is (phew!), but that stops happening with some upcoming patches. As a trivial example, the following code: void test_fallback(struct timespec *ts) { vdso_fallback_gettime(CLOCK_MONOTONIC, ts); } compiles to: 00000000000000c0 : c0: c3 retq To add insult to injury, the RCX and R11 clobbers on 64-bit builds were missing. The "memory" clobber is also unnecessary -- no ordering with respect to other memory operations is needed, but that's going to be fixed in a separate not-for-stable patch. Fixes: 2aae950b21e4 ("x86_64: Add vDSO for x86-64 with gettimeofday/clock_gettime/getcpu") Signed-off-by: Andy Lutomirski Signed-off-by: Thomas Gleixner Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/2c0231690551989d2fafa60ed0e7b5cc8b403908.1538422295.git.luto@kernel.org Signed-off-by: Greg Kroah-Hartman --- arch/x86/vdso/vclock_gettime.c | 18 ++++++++++-------- 1 file changed, 10 insertions(+), 8 deletions(-) --- a/arch/x86/vdso/vclock_gettime.c +++ b/arch/x86/vdso/vclock_gettime.c @@ -46,8 +46,9 @@ static notrace cycle_t vread_hpet(void) notrace static long vdso_fallback_gettime(long clock, struct timespec *ts) { long ret; - asm("syscall" : "=a" (ret) : - "0" (__NR_clock_gettime), "D" (clock), "S" (ts) : "memory"); + asm ("syscall" : "=a" (ret), "=m" (*ts) : + "0" (__NR_clock_gettime), "D" (clock), "S" (ts) : + "memory", "rcx", "r11"); return ret; } @@ -55,8 +56,9 @@ notrace static long vdso_fallback_gtod(s { long ret; - asm("syscall" : "=a" (ret) : - "0" (__NR_gettimeofday), "D" (tv), "S" (tz) : "memory"); + asm ("syscall" : "=a" (ret), "=m" (*tv), "=m" (*tz) : + "0" (__NR_gettimeofday), "D" (tv), "S" (tz) : + "memory", "rcx", "r11"); return ret; } @@ -136,12 +138,12 @@ notrace static long vdso_fallback_gettim { long ret; - asm( + asm ( "mov %%ebx, %%edx \n" "mov %2, %%ebx \n" "call __kernel_vsyscall \n" "mov %%edx, %%ebx \n" - : "=a" (ret) + : "=a" (ret), "=m" (*ts) : "0" (__NR_clock_gettime), "g" (clock), "c" (ts) : "memory", "edx"); return ret; @@ -151,12 +153,12 @@ notrace static long vdso_fallback_gtod(s { long ret; - asm( + asm ( "mov %%ebx, %%edx \n" "mov %2, %%ebx \n" "call __kernel_vsyscall \n" "mov %%edx, %%ebx \n" - : "=a" (ret) + : "=a" (ret), "=m" (*tv), "=m" (*tz) : "0" (__NR_gettimeofday), "g" (tv), "c" (tz) : "memory", "edx"); return ret;