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Message-ID: <CAJcbSZGWX23QTWmM4a_07ui-8Xyz4H2NLj1LXFFbZvnv9tc_XQ@mail.gmail.com> Date: Tue, 4 Apr 2017 12:21:48 -0700 From: Thomas Garnier <thgarnie@...gle.com> To: "H. Peter Anvin" <hpa@...or.com> Cc: Martin Schwidefsky <schwidefsky@...ibm.com>, Heiko Carstens <heiko.carstens@...ibm.com>, Dave Hansen <dave.hansen@...el.com>, Arnd Bergmann <arnd@...db.de>, Thomas Gleixner <tglx@...utronix.de>, Al Viro <viro@...iv.linux.org.uk>, David Howells <dhowells@...hat.com>, René Nyffenegger <mail@...enyffenegger.ch>, Andrew Morton <akpm@...ux-foundation.org>, "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>, Ingo Molnar <mingo@...nel.org>, Oleg Nesterov <oleg@...hat.com>, Stephen Smalley <sds@...ho.nsa.gov>, Pavel Tikhomirov <ptikhomirov@...tuozzo.com>, Ingo Molnar <mingo@...hat.com>, Andy Lutomirski <luto@...nel.org>, Paolo Bonzini <pbonzini@...hat.com>, Kees Cook <keescook@...omium.org>, Rik van Riel <riel@...hat.com>, Josh Poimboeuf <jpoimboe@...hat.com>, Borislav Petkov <bp@...en8.de>, Brian Gerst <brgerst@...il.com>, "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>, Christian Borntraeger <borntraeger@...ibm.com>, Russell King <linux@...linux.org.uk>, Will Deacon <will.deacon@....com>, Catalin Marinas <catalin.marinas@....com>, Mark Rutland <mark.rutland@....com>, James Morse <james.morse@....com>, linux-s390 <linux-s390@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, Linux API <linux-api@...r.kernel.org>, "the arch/x86 maintainers" <x86@...nel.org>, linux-arm-kernel@...ts.infradead.org, Kernel Hardening <kernel-hardening@...ts.openwall.com> Subject: Re: [PATCH v6 2/4] x86/syscalls: Specific usage of verify_pre_usermode_state On Tue, Apr 4, 2017 at 11:27 AM, H. Peter Anvin <hpa@...or.com> 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
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