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Date: Tue, 04 Apr 2017 15:34:30 -0700 From: "H. Peter Anvin" <hpa@...or.com> To: Thomas Garnier <thgarnie@...gle.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@...or.com Subject: Re: [PATCH v6 2/4] x86/syscalls: Specific usage of verify_pre_usermode_state <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> From: hpa@...or.com Message-ID: <C92745AD-C4D9-441E-854C-985512E5FD8F@...or.com> On April 4, 2017 12:21:48 PM PDT, Thomas Garnier <thgarnie@...gle.com> wrote: >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 >> Easier for you, perhaps, but not for everyone else... -- Sent from my Android device with K-9 Mail. Please excuse my brevity.
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