Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755085AbdDDW4d convert rfc822-to-8bit (ORCPT ); Tue, 4 Apr 2017 18:56:33 -0400 Received: from terminus.zytor.com ([65.50.211.136]:44823 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753364AbdDDW4b (ORCPT ); Tue, 4 Apr 2017 18:56:31 -0400 From: "H. Peter Anvin" Message-Id: <201704042234.v34MYagd031215@mail.zytor.com> Date: Tue, 04 Apr 2017 15:34:30 -0700 User-Agent: K-9 Mail for Android In-Reply-To: References: <20170404174727.35478-1-thgarnie@google.com> <20170404174727.35478-2-thgarnie@google.com> <05d9c4a7-8acb-5997-1dd6-d534398e6f54@zytor.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Subject: Re: [PATCH v6 2/4] x86/syscalls: Specific usage of verify_pre_usermode_state To: Thomas Garnier CC: Martin Schwidefsky , Heiko Carstens , Dave Hansen , Arnd Bergmann , Thomas Gleixner , Al Viro , David Howells , =?ISO-8859-1?Q?Ren=E9_Nyffenegger?= , Andrew Morton , "Paul E . McKenney" , Ingo Molnar , Oleg Nesterov , Stephen Smalley , Pavel Tikhomirov , Ingo Molnar , Andy Lutomirski , Paolo Bonzini , Kees Cook , Rik van Riel , Josh Poimboeuf , Borislav Petkov , Brian Gerst , "Kirill A . Shutemov" , Christian Borntraeger , Russell King , Will.Deacon@zytor.com Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3443 Lines: 84 ,Catalin Marinas ,Mark Rutland ,James Morse ,linux-s390 ,LKML ,Linux API ,the arch/x86 maintainers ,linux-arm-kernel@lists.infradead.org,Kernel Hardening From: hpa@zytor.com Message-ID: On April 4, 2017 12:21:48 PM PDT, Thomas Garnier wrote: >On Tue, Apr 4, 2017 at 11:27 AM, H. Peter Anvin wrote: >> On 04/04/17 10:47, Thomas Garnier wrote: >>> diff --git a/arch/x86/include/asm/pgtable_64_types.h >b/arch/x86/include/asm/pgtable_64_types.h >>> index 516593e66bd6..12fa851c7fa8 100644 >>> --- a/arch/x86/include/asm/pgtable_64_types.h >>> +++ b/arch/x86/include/asm/pgtable_64_types.h >>> @@ -78,4 +78,15 @@ typedef struct { pteval_t pte; } pte_t; >>> >>> #define EARLY_DYNAMIC_PAGE_TABLES 64 >>> >>> +/* >>> + * User space process size. 47bits minus one guard page. The guard >>> + * page is necessary on Intel CPUs: if a SYSCALL instruction is at >>> + * the highest possible canonical userspace address, then that >>> + * syscall will enter the kernel with a non-canonical return >>> + * address, and SYSRET will explode dangerously. We avoid this >>> + * particular problem by preventing anything from being mapped >>> + * at the maximum canonical address. >>> + */ >>> +#define TASK_SIZE_MAX ((_AC(1, UL) << 47) - PAGE_SIZE) >>> + >>> #endif /* _ASM_X86_PGTABLE_64_DEFS_H */ >>> diff --git a/arch/x86/include/asm/processor.h >b/arch/x86/include/asm/processor.h >>> index 3cada998a402..e80822582d3e 100644 >>> --- a/arch/x86/include/asm/processor.h >>> +++ b/arch/x86/include/asm/processor.h >>> @@ -825,17 +825,6 @@ static inline void spin_lock_prefetch(const >void *x) >>> #define KSTK_ESP(task) (task_pt_regs(task)->sp) >>> >>> #else >>> -/* >>> - * User space process size. 47bits minus one guard page. The guard >>> - * page is necessary on Intel CPUs: if a SYSCALL instruction is at >>> - * the highest possible canonical userspace address, then that >>> - * syscall will enter the kernel with a non-canonical return >>> - * address, and SYSRET will explode dangerously. We avoid this >>> - * particular problem by preventing anything from being mapped >>> - * at the maximum canonical address. >>> - */ >>> -#define TASK_SIZE_MAX ((1UL << 47) - PAGE_SIZE) >>> - >>> /* This decides where the kernel will search for a free chunk of vm >>> * space during mmap's. >>> */ >>> >> >> This should be an entirely separate patch; if nothing else you need >to >> explain it in the comments. > >I will explain it in the commit message, it should be easier than a >separate patch. > >> >> Also, you say this is for "x86", but I still don't see any code for >i386 >> whatsoever. Have you verified *all* the i386 and i386-compat paths >to >> make sure they go via prepare_exit_to_usermode()? [Cc: Andy] > >I did but I will do it again for the next iteration. > >> >> Finally, I can't really believe I'm the only person for whom >"Specific >> usage of verity_pre_usermode_state" is completely opaque. > >I agree, I will improve it. > >> >> -hpa >> Easier for you, perhaps, but not for everyone else... -- Sent from my Android device with K-9 Mail. Please excuse my brevity.