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Message-ID: <CAMzpN2jmW3FmKXZmHNaK537oTdcrDvqatEYZk=aT2B7Qx=fEuA@mail.gmail.com>
Date: Tue, 9 May 2017 12:05:12 -0400
From: Brian Gerst <brgerst@...il.com>
To: Andy Lutomirski <luto@...nel.org>
Cc: Christoph Hellwig <hch@...radead.org>, Ingo Molnar <mingo@...nel.org>, Greg KH <greg@...ah.com>,
Thomas Garnier <thgarnie@...gle.com>, 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>, David Howells <dhowells@...hat.com>,
René Nyffenegger <mail@...enyffenegger.ch>,
Andrew Morton <akpm@...ux-foundation.org>,
"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>, "Eric W . Biederman" <ebiederm@...ssion.com>,
Oleg Nesterov <oleg@...hat.com>, Pavel Tikhomirov <ptikhomirov@...tuozzo.com>,
Ingo Molnar <mingo@...hat.com>, "H . Peter Anvin" <hpa@...or.com>, Paolo Bonzini <pbonzini@...hat.com>,
Rik van Riel <riel@...hat.com>, Kees Cook <keescook@...omium.org>,
Josh Poimboeuf <jpoimboe@...hat.com>, Borislav Petkov <bp@...en8.de>,
"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" <linux-arm-kernel@...ts.infradead.org>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
Linus Torvalds <torvalds@...ux-foundation.org>, Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: Re: [PATCH v9 1/4] syscalls: Verify address
limit before returning to user-mode
On Tue, May 9, 2017 at 9:00 AM, Andy Lutomirski <luto@...nel.org> wrote:
> On Tue, May 9, 2017 at 1:56 AM, Christoph Hellwig <hch@...radead.org> wrote:
>> On Tue, May 09, 2017 at 08:45:22AM +0200, Ingo Molnar wrote:
>>> We only have ~115 code blocks in the kernel that set/restore KERNEL_DS, it would
>>> be a pity to add a runtime check to every system call ...
>>
>> I think we should simply strive to remove all of them that aren't
>> in core scheduler / arch code. Basically evetyytime we do the
>>
>> oldfs = get_fs();
>> set_fs(KERNEL_DS);
>> ..
>> set_fs(oldfs);
>>
>> trick we're doing something wrong, and there should always be better
>> ways to archive it. E.g. using iov_iter with a ITER_KVEC type
>> consistently would already remove most of them.
>
> How about trying to remove all of them? If we could actually get rid
> of all of them, we could drop the arch support, and we'd get faster,
> simpler, shorter uaccess code throughout the kernel.
>
> The ones in kernel/compat.c are generally garbage. They should be
> using compat_alloc_user_space(). Ditto for kernel/power/user.c.
compat_alloc_user_space() is a hack that should go away too. It ends
up copying the data three times.
The more efficient solution to this is to have a core syscall function
that only accesses kernel memory, and then have two front-end
functions (native and compat) that do the actual reads and writes to
userspace, with conversion in the compat case.
--
Brian Gerst
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