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Date: Fri, 12 May 2017 21:45:56 +0100
From: Russell King - ARM Linux <linux@...linux.org.uk>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Mark Rutland <mark.rutland@....com>, Brian Gerst <brgerst@...il.com>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
Catalin Marinas <catalin.marinas@....com>,
Heiko Carstens <heiko.carstens@...ibm.com>,
Oleg Nesterov <oleg@...hat.com>,
David Howells <dhowells@...hat.com>,
Dave Hansen <dave.hansen@...el.com>,
"H . Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
Pavel Tikhomirov <ptikhomirov@...tuozzo.com>,
linux-s390 <linux-s390@...r.kernel.org>,
the arch/x86 maintainers <x86@...nel.org>,
Christian Borntraeger <borntraeger@...ibm.com>,
René Nyffenegger <mail@...enyffenegger.ch>,
Greg KH <greg@...ah.com>,
"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
Rik van Riel <riel@...hat.com>, Kees Cook <keescook@...omium.org>,
Arnd Bergmann <arnd@...db.de>, Will Deacon <will.deacon@....com>,
Borislav Petkov <bp@...en8.de>, Al Viro <viro@...iv.linux.org.uk>,
Andy Lutomirski <luto@...nel.org>,
Josh Poimboeuf <jpoimboe@...hat.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
Linux API <linux-api@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>,
Daniel Micay <danielmicay@...il.com>,
James Morse <james.morse@....com>,
"Eric W . Biederman" <ebiederm@...ssion.com>,
Martin Schwidefsky <schwidefsky@...ibm.com>,
Paolo Bonzini <pbonzini@...hat.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Linus Torvalds <torvalds@...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 10:30:44PM +0200, Peter Zijlstra wrote:
> 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.
I hope their size is appropriately limited, but something tells me it
would be foolish to assume that.
> But yes, fully agreed on the desirability of alloca() and things.
Hmm, I wonder if -fno-builtin-alloca would prevent those... it looks
like it certainly would prevent an explicit alloca() call.
--
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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