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Date: Mon, 8 May 2017 08:26:23 -0700
From: Kees Cook <>
To: Daniel Micay <>
Cc: Ingo Molnar <>, Thomas Garnier <>, 
	Martin Schwidefsky <>, Heiko Carstens <>, 
	Dave Hansen <>, Arnd Bergmann <>, 
	Thomas Gleixner <>, David Howells <>, 
	René Nyffenegger <>, 
	Andrew Morton <>, 
	"Paul E . McKenney" <>, "Eric W . Biederman" <>, 
	Oleg Nesterov <>, Pavel Tikhomirov <>, 
	Ingo Molnar <>, "H . Peter Anvin" <>, Andy Lutomirski <>, 
	Paolo Bonzini <>, 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" <>, 
	"" <>, 
	Kernel Hardening <>, 
	Linus Torvalds <>, Peter Zijlstra <>
Subject: Re: Re: [PATCH v9 1/4] syscalls: Verify address
 limit before returning to user-mode

On Mon, May 8, 2017 at 8:22 AM, Daniel Micay <> wrote:
> On Mon, 2017-05-08 at 09:52 +0200, Ingo Molnar wrote:
>> ... it's just not usable in that form for a regular maintenance flow.
>> So what would be more useful is to add a specific Sparse check that
>> only checks
>> KERNEL_DS, to add it as a regular (.config driven) build option and
>> make sure the
>> kernel build has zero warnings.
>> From that point on we can declare that this kind of bug won't occur
>> anymore, if
>> the Sparse implementation of the check is correct.
>> But there's a (big) problem with that development model: Sparse is not
>> part of the
>> kernel tree and adding a feature to it while making the kernel depend
>> on that
>> brand new feature is a logistical nightmare. The overhead is quite
>> similar to
>> adding new features to a compiler - it happens at a glacial pace and
>> is only done
>> for major features really, at considerable expense. I don't think this
>> is an
>> adequate model for 'extended syntax checking' of the kernel,
>> especially when it
>> comes to correctness that has such obvious security impact.
>> Thanks,
>>       Ingo
> There's the option of using GCC plugins now that the infrastructure was
> upstreamed from grsecurity. It can be used as part of the regular build
> process and as long as the analysis is pretty simple it shouldn't hurt
> compile time much.

Well, and that the situation may arise due to memory corruption, not
from poorly-matched set_fs() calls, which static analysis won't help
solve. We need to catch this bad kernel state because it is a very bad
state to run in.


Kees Cook
Pixel Security

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