kernel-hardening - Re: Re: [PATCH v9 1/4] syscalls: Verify address limit before returning to user-mode

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Date: Tue, 9 May 2017 08:45:22 +0200
From: Ingo Molnar <mingo@...nel.org>
To: Greg KH <greg@...ah.com>
Cc: 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>,
	Andy Lutomirski <luto@...nel.org>,
	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>, 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>,
	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

* Greg KH <greg@...ah.com> wrote:

> What about a simple coccinelle script to test for this type of thing?
> We write it once, add it to the in-kernel body of tests, and then 0-day
> runs it on all trees all the time.  That should catch this type of
> issue, like all of the other "bad programming bus" that the tool
> currently catches.

Yeah, that would work - but today most of our coccinelle scripts are still pretty 
verbose, and I think it's important to make this a different category of 
coccinelle script, which is .config driven where a loud warning yells at us.

I.e. force the 'zero warnings tolerated' model.

I also noticed that Coccinelle builds are pretty slow, so it would still make 
sense to have a performance oriented static checking facility that does not have 
the performance baggage of high level functional languages.

I.e. either integrate it into Sparse - or start a kernel integrated static 
analysis tooling project that would only follow control flow initially - which is 
what we need here I believe.

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 ...

We could also add a runtime check to oops handling to make sure we don't leak 
KERNEL_DS through kernel crashes, to ease worries about CVE-2010-4258.

Thanks,

	Ingo

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