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Date: Mon, 8 May 2017 16:02:30 +0200
From: Ingo Molnar <mingo@...nel.org>
To: Kees Cook <keescook@...omium.org>
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>,
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" <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: [PATCH v9 1/4] syscalls: Verify address limit before returning
to user-mode
* Kees Cook <keescook@...omium.org> wrote:
> > And yes, I realize that there were other such bugs and that such bugs might
> > occur in the future - but why not push the overhead of the security check to
> > the kernel build phase? I.e. I'm wondering how well we could do static
> > analysis during kernel build - would a limited mode of Sparse be good enough
> > for that? Or we could add a new static checker to tools/, built from first
> > principles and used primarily for extended syntactical checking.
>
> Static analysis is just not going to cover all cases. We've had vulnerabilities
> where interrupt handlers left KERNEL_DS set, for example. [...]
Got any commit ID of that bug - was it because a function executed by the
interrupt handler leaked KERNEL_DS?
> [...] If there are performance concerns, let's put this behind a CONFIG. 2-5
> instructions is not an issue for most people that want this coverage.
That doesn't really _solve_ the performance concerns, it just forces most people
to enable it by creating a 'security or performance' false dichotomy ...
> [...] and it still won't catch everything. Bug-finding is different from making
> a bug class just unexploitable at all. As we've done before, it's the difference
> between trying to find format string attacks vs just removing %n from the format
> parser.
No, it does not make it unexploitable, it could still be exploitable if the
runtime check is buggy or if there's kernel execution outside of the regular
system call paths - there's plenty of such hardware functionality on x86 for
example.
Thanks,
Ingo
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