From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753311AbdGMUeV (ORCPT ); Thu, 13 Jul 2017 16:34:21 -0400 Received: from mx1.redhat.com ([209.132.183.28]:36456 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753136AbdGMUeT (ORCPT ); Thu, 13 Jul 2017 16:34:19 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com A804E8F037 Authentication-Results: ext-mx02.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx02.extmail.prod.ext.phx2.redhat.com; spf=pass smtp.mailfrom=jpoimboe@redhat.com DKIM-Filter: OpenDKIM Filter v2.11.0 mx1.redhat.com A804E8F037 Date: Thu, 13 Jul 2017 15:34:16 -0500 From: Josh Poimboeuf To: Andrey Rybainin Cc: Matthias Kaehlcke , Chris J Arges , Borislav Petkov , Thomas Gleixner , Ingo Molnar , "H . Peter Anvin" , x86@kernel.org, linux-kernel@vger.kernel.org, Douglas Anderson , Michael Davidson , Greg Hackmann , Nick Desaulniers , Stephen Hines , Kees Cook , Arnd Bergmann , Bernhard.Rosenkranzer@linaro.org Subject: Re: [PATCH] Revert "x86/uaccess: Add stack frame output operand in get_user() inline asm" Message-ID: <20170713203416.isvijqbwbcgupgj7@treble> References: <20170712212744.23660-1-mka@chromium.org> <20170712221242.puv5illztsla4nph@treble> <20170712222040.GD95735@google.com> <20170712223547.fyra43dizqooosbs@treble> <20170712223630.gb237t4vhrqeu5zd@treble> <20170712232213.GE95735@google.com> <20170713180001.mvwzdmudht56hdk5@treble> <20170713184748.GF95735@google.com> <75850bb7-a60e-057d-d88b-afa0c79e94a0@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <75850bb7-a60e-057d-d88b-afa0c79e94a0@gmail.com> User-Agent: Mutt/1.6.0.1 (2016-04-01) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.26]); Thu, 13 Jul 2017 20:34:19 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 13, 2017 at 11:20:04PM +0300, Andrey Rybainin wrote: > On 07/13/2017 09:47 PM, Matthias Kaehlcke wrote: > > > Thanks for your analysis! > > > >> What happens if you try the below patch instead of the revert? Any > >> chance the offending instruction goes away? > >> > >> diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h > >> index 11433f9..beac907 100644 > >> --- a/arch/x86/include/asm/uaccess.h > >> +++ b/arch/x86/include/asm/uaccess.h > >> @@ -171,7 +171,7 @@ __typeof__(__builtin_choose_expr(sizeof(x) > sizeof(0UL), 0ULL, 0UL)) > >> might_fault(); \ > >> asm volatile("call __get_user_%P4" \ > >> : "=a" (__ret_gu), "=r" (__val_gu), "+r" (__sp) \ > >> - : "0" (ptr), "i" (sizeof(*(ptr)))); \ > >> + : "0" (ptr), "i" (sizeof(*(ptr))), "r" (__sp)); \ > >> (x) = (__force __typeof__(*(ptr))) __val_gu; \ > >> __builtin_expect(__ret_gu, 0); \ > >> }) > > > > The generated code is basically the same, only that now the value from > > the stack is stored in a register and written twice to RSP: > > > > AFAIR clang works much better with global named registers. > Could you check if the patch bellow helps? And yet another one to try (clobbering sp) :-) diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h index 11433f9..21f0c39 100644 --- a/arch/x86/include/asm/uaccess.h +++ b/arch/x86/include/asm/uaccess.h @@ -166,12 +166,12 @@ __typeof__(__builtin_choose_expr(sizeof(x) > sizeof(0UL), 0ULL, 0UL)) ({ \ int __ret_gu; \ register __inttype(*(ptr)) __val_gu asm("%"_ASM_DX); \ - register void *__sp asm(_ASM_SP); \ __chk_user_ptr(ptr); \ might_fault(); \ - asm volatile("call __get_user_%P4" \ - : "=a" (__ret_gu), "=r" (__val_gu), "+r" (__sp) \ - : "0" (ptr), "i" (sizeof(*(ptr)))); \ + asm volatile("call __get_user_%P3" \ + : "=a" (__ret_gu), "=r" (__val_gu) \ + : "0" (ptr), "i" (sizeof(*(ptr))) \ + : "sp"); \ (x) = (__force __typeof__(*(ptr))) __val_gu; \ __builtin_expect(__ret_gu, 0); \ })