Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755344AbdDDTVw (ORCPT ); Tue, 4 Apr 2017 15:21:52 -0400 Received: from mail-io0-f180.google.com ([209.85.223.180]:32783 "EHLO mail-io0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755269AbdDDTVu (ORCPT ); Tue, 4 Apr 2017 15:21:50 -0400 MIME-Version: 1.0 In-Reply-To: <05d9c4a7-8acb-5997-1dd6-d534398e6f54@zytor.com> References: <20170404174727.35478-1-thgarnie@google.com> <20170404174727.35478-2-thgarnie@google.com> <05d9c4a7-8acb-5997-1dd6-d534398e6f54@zytor.com> From: Thomas Garnier Date: Tue, 4 Apr 2017 12:21:48 -0700 Message-ID: Subject: Re: [PATCH v6 2/4] x86/syscalls: Specific usage of verify_pre_usermode_state To: "H. Peter Anvin" Cc: Martin Schwidefsky , Heiko Carstens , Dave Hansen , Arnd Bergmann , Thomas Gleixner , Al Viro , David Howells , =?UTF-8?Q?Ren=C3=A9_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 , Catalin Marinas , Mark Rutland , James Morse , linux-s390 , LKML , Linux API , "the arch/x86 maintainers" , linux-arm-kernel@lists.infradead.org, Kernel Hardening Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2712 Lines: 73 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 > -- Thomas