Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752593AbdGMV1s (ORCPT ); Thu, 13 Jul 2017 17:27:48 -0400 Received: from mail-lf0-f67.google.com ([209.85.215.67]:34931 "EHLO mail-lf0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751153AbdGMV1r (ORCPT ); Thu, 13 Jul 2017 17:27:47 -0400 Subject: Re: [PATCH] Revert "x86/uaccess: Add stack frame output operand in get_user() inline asm" To: Matthias Kaehlcke Cc: Josh Poimboeuf , Chris J Arges , Borislav Petkov , Thomas Gleixner , Ingo Molnar , "H . Peter Anvin" , x86@kernel.org, Linux Kernel Mailing List , Douglas Anderson , Michael Davidson , Greg Hackmann , Nick Desaulniers , Stephen Hines , Kees Cook , Arnd Bergmann , =?UTF-8?Q?Bernhard_Rosenkr=c3=a4nzer?= 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> <20170713211414.GH95735@google.com> From: Andrey Rybainin Message-ID: Date: Fri, 14 Jul 2017 00:25:42 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.0 MIME-Version: 1.0 In-Reply-To: <20170713211414.GH95735@google.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3127 Lines: 81 On 07/14/2017 12:14 AM, Matthias Kaehlcke wrote: > El Thu, Jul 13, 2017 at 11:20:04PM +0300 Andrey Rybainin ha dit: > >> 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? >> >> >> --- >> arch/x86/include/asm/uaccess.h | 7 +++++-- >> 1 file changed, 5 insertions(+), 2 deletions(-) >> >> diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h >> index a059aac9e937..121204387978 100644 >> --- a/arch/x86/include/asm/uaccess.h >> +++ b/arch/x86/include/asm/uaccess.h >> @@ -157,15 +157,18 @@ __typeof__(__builtin_choose_expr(sizeof(x) > sizeof(0UL), 0ULL, 0UL)) >> * Clang/LLVM cares about the size of the register, but still wants >> * the base register for something that ends up being a pair. >> */ >> + >> +register unsigned long __current_sp asm(_ASM_SP); >> + >> #define get_user(x, ptr) \ >> ({ \ >> 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) \ >> + : "=a" (__ret_gu), "=r" (__val_gu), \ >> + "+r" (__current_sp) \ >> : "0" (ptr), "i" (sizeof(*(ptr)))); \ >> (x) = (__force __typeof__(*(ptr))) __val_gu; \ >> __builtin_expect(__ret_gu, 0); \ > > Thanks for the suggestion, however it fails to build with both gcc and clang: > > fs/ioctl.c:585:6: error: use of undeclared identifier '__current_sp' > if (get_user(count, &argp->dest_count)) { > ^ > arch/x86/include/asm/uaccess.h:168:16: note: expanded from macro 'get_user' > "+r" (__current_sp) > \ > > The references I found refer to __current_sp as an intrinsic function > for ARM32. What? __current_sp declared right above get_user() as "register unsigned long __current_sp asm(_ASM_SP);" Did you actually applied my patch or you just modified the code yourself but have missed "register unsigned long __current_sp asm(_ASM_SP);" ? FWIW patch works (builds) for me with gcc.