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Message-ID: <20170512203044.GI4626@worktop.programming.kicks-ass.net>
Date: Fri, 12 May 2017 22:30:44 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Russell King - ARM Linux <linux@...linux.org.uk>
Cc: Kees Cook <keescook@...omium.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Mark Rutland <mark.rutland@....com>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
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LKML <linux-kernel@...r.kernel.org>,
David Howells <dhowells@...hat.com>,
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"H . Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
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linux-s390 <linux-s390@...r.kernel.org>,
the arch/x86 maintainers <x86@...nel.org>,
Will Deacon <will.deacon@....com>,
Christian Borntraeger <borntraeger@...ibm.com>,
René Nyffenegger <mail@...enyffenegger.ch>,
Catalin Marinas <catalin.marinas@....com>,
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Al Viro <viro@...iv.linux.org.uk>,
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Josh Poimboeuf <jpoimboe@...hat.com>,
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Andrew Morton <akpm@...ux-foundation.org>,
Thomas Garnier <thgarnie@...gle.com>,
"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: Re: [PATCH v9 1/4] syscalls: Verify address
limit before returning to user-mode
On Fri, May 12, 2017 at 09:21:06PM +0100, Russell King - ARM Linux wrote:
> On Fri, May 12, 2017 at 12:30:02PM -0700, Kees Cook wrote:
> > I'm clearly not explaining things well enough. I shouldn't say
> > "corruption", I should say "malicious manipulation". The methodology
> > of attacks against the stack are quite different from the other kinds
> > of attacks like use-after-free, heap overflow, etc. Being able to
> > exhaust the kernel stack (either due to deep recursion or unbounded
> > alloca())
>
> I really hope we don't have alloca() use in the kernel. Do you have
> evidence to support that assertion?
>
> IMHO alloca() (or similar) should not be present in any kernel code
> because we have a limited stack - we have kmalloc() etc for that kind
> of thing.
On stack variable length arrays get implemented by the compiler doing
alloca(), and we sadly have a few of those around.
But yes, fully agreed on the desirability of alloca() and things.
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