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Date: Fri, 12 May 2017 22:30:44 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Russell King - ARM Linux <linux@armlinux.org.uk>
Cc: Kees Cook <keescook@chromium.org>,
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Subject: Re: [kernel-hardening] Re: [PATCH v9 1/4] syscalls: Verify address
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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.