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

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Message-ID: <20170509064522.anusoikaalvlux3w@gmail.com>
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: [kernel-hardening] 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