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>, Greg KH <greg@...ah.com>, Heiko Carstens <heiko.carstens@...ibm.com>, LKML <linux-kernel@...r.kernel.org>, 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>, Will Deacon <will.deacon@....com>, Christian Borntraeger <borntraeger@...ibm.com>, René Nyffenegger <mail@...enyffenegger.ch>, Catalin Marinas <catalin.marinas@....com>, "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>, Rik van Riel <riel@...hat.com>, Arnd Bergmann <arnd@...db.de>, Brian Gerst <brgerst@...il.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>, Oleg Nesterov <oleg@...hat.com>, 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>, 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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