From: "H. Peter Anvin" <hpa-YMNOUZJC4hwAvxtiuMwx3w@public.gmane.org>
To: Thomas Garnier <thgarnie-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
Cc: "Martin Schwidefsky"
<schwidefsky-tA70FqPdS9bQT0dZR+AlfA@public.gmane.org>,
"Heiko Carstens"
<heiko.carstens-tA70FqPdS9bQT0dZR+AlfA@public.gmane.org>,
"Dave Hansen"
<dave.hansen-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>,
"Arnd Bergmann" <arnd-r2nGTMty4D4@public.gmane.org>,
"Thomas Gleixner" <tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>,
"Al Viro"
<viro-RmSDqhL/yNMiFSDQTTA3OLVCufUGDwFn@public.gmane.org>,
"David Howells"
<dhowells-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
"René Nyffenegger"
<mail-gLCNRsNSrVdVZEhyV+6z5nIPMjoJpjVV@public.gmane.org>,
"Andrew Morton"
<akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>,
"Paul E . McKenney"
<paulmck-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>,
"Ingo Molnar" <mingo-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
"Oleg Nesterov" <oleg-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
"Stephen Smalley" <sds-+05T5uksL2qpZYMLLGbcSA@public.gmane.org>,
"Pavel Tikhomirov"
<ptikhomirov-5HdwGun5lf+gSpxsJD1C4w@public.gmane.org>,
"Ingo Molnar" <mingo-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
"Andy Lutomirski" <luto-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
"Paolo Bonzini"
<pbonzini-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
"Kees Cook" <keescook-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>,
"Rik van Riel" <riel-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Subject: Re: [PATCH v6 2/4] x86/syscalls: Specific usage of verify_pre_usermode_state
Date: Tue, 04 Apr 2017 15:34:30 -0700 [thread overview]
Message-ID: <201704042234.v34MYagd031215@mail.zytor.com> (raw)
In-Reply-To: <CAJcbSZGWX23QTWmM4a_07ui-8Xyz4H2NLj1LXFFbZvnv9tc_XQ-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
<will.deacon-5wv7dgnIgG8@public.gmane.org>,Catalin Marinas <catalin.marinas-5wv7dgnIgG8@public.gmane.org>,Mark Rutland <mark.rutland-5wv7dgnIgG8@public.gmane.org>,James Morse <james.morse-5wv7dgnIgG8@public.gmane.org>,linux-s390 <linux-s390-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,LKML <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,Linux API <linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,the arch/x86 maintainers <x86-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org,Kernel Hardening <kernel-hardening-ZwoEplunGu1jrUoiu81ncdBPR1lH4CV8@public.gmane.org>
From: hpa-YMNOUZJC4hwAvxtiuMwx3w@public.gmane.org
Message-ID: <C92745AD-C4D9-441E-854C-985512E5FD8F-YMNOUZJC4hwAvxtiuMwx3w@public.gmane.org>
On April 4, 2017 12:21:48 PM PDT, Thomas Garnier <thgarnie-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org> wrote:
>On Tue, Apr 4, 2017 at 11:27 AM, H. Peter Anvin <hpa-YMNOUZJC4hwAvxtiuMwx3w@public.gmane.org> 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.
next prev parent reply other threads:[~2017-04-04 22:34 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-04 17:47 [PATCH v6 1/4] syscalls: Restore address limit after a syscall Thomas Garnier
[not found] ` <20170404174727.35478-1-thgarnie-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
2017-04-04 17:47 ` [PATCH v6 2/4] x86/syscalls: Specific usage of verify_pre_usermode_state Thomas Garnier
2017-04-04 18:11 ` H. Peter Anvin
2017-04-04 18:27 ` H. Peter Anvin
[not found] ` <05d9c4a7-8acb-5997-1dd6-d534398e6f54-YMNOUZJC4hwAvxtiuMwx3w@public.gmane.org>
2017-04-04 18:54 ` Borislav Petkov
2017-04-04 19:21 ` Thomas Garnier
[not found] ` <CAJcbSZGWX23QTWmM4a_07ui-8Xyz4H2NLj1LXFFbZvnv9tc_XQ-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-04-04 22:34 ` H. Peter Anvin [this message]
2017-04-04 17:47 ` [PATCH v6 4/4] arm64/syscalls: " Thomas Garnier
2017-04-05 14:22 ` Catalin Marinas
2017-04-05 14:36 ` Thomas Garnier
2017-04-05 17:49 ` Catalin Marinas
2017-04-05 18:14 ` Thomas Garnier
2017-04-07 16:11 ` Catalin Marinas
2017-04-04 17:47 ` [PATCH v6 3/4] arm/syscalls: " Thomas Garnier
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