From mboxrd@z Thu Jan  1 00:00:00 1970
From: viro@ZenIV.linux.org.uk (Al Viro)
Date: Fri, 12 May 2017 22:06:46 +0100
Subject: [kernel-hardening] Re: [PATCH v9 1/4] syscalls: Verify address
 limit before returning to user-mode
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Message-ID: <20170512210645.GS390@ZenIV.linux.org.uk>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

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.

No alloca(), but there are VLAs.  Said that, the whole "what if they
can bugger thread_info and/or task_struct and go after set_fs() state"
is idiocy, of course - in that case the box is fucked, no matter what.