Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752857AbdGMVn3 (ORCPT ); Thu, 13 Jul 2017 17:43:29 -0400 Received: from mail-pf0-f169.google.com ([209.85.192.169]:35060 "EHLO mail-pf0-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752446AbdGMVn2 (ORCPT ); Thu, 13 Jul 2017 17:43:28 -0400 Date: Thu, 13 Jul 2017 14:43:26 -0700 From: Matthias Kaehlcke To: Andrey Rybainin 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 , Bernhard =?utf-8?Q?Rosenkr=C3=A4nzer?= Subject: Re: [PATCH] Revert "x86/uaccess: Add stack frame output operand in get_user() inline asm" Message-ID: <20170713214326.GI95735@google.com> References: <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> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3605 Lines: 88 El Fri, Jul 14, 2017 at 12:25:42AM +0300 Andrey Rybainin ha dit: > > > 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);" ? Indeed, since the patch is only a few lines and I had the function already open in the editor it seemed easier to change the affected lines than to apply the patch and I missed the definition <:‑| After adding the missing line the code builds with clang and the stack pointer is not corrupted.