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Message-ID: <1494625675.29205.21.camel@redhat.com>
Date: Fri, 12 May 2017 17:47:55 -0400
From: Rik van Riel <riel@...hat.com>
To: Al Viro <viro@...IV.linux.org.uk>, Kees Cook <keescook@...omium.org>
Cc: Russell King - ARM Linux <linux@...linux.org.uk>, 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>, Peter Zijlstra
<a.p.zijlstra@...llo.nl>, Arnd Bergmann <arnd@...db.de>, Brian Gerst
<brgerst@...il.com>, Borislav Petkov <bp@...en8.de>, 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, 2017-05-12 at 22:41 +0100, Al Viro wrote:
> On Fri, May 12, 2017 at 02:17:19PM -0700, Kees Cook wrote:
>
> > Two things are at risk from stack exhaustion: thread_info (mainly
> > addr_limit) when on the stack (fixed by THREAD_INFO_IN_TASK), and
>
> Really? Let's take a look at arm, for example:
>
> struct thread_info {
> unsigned long flags; /* low level flags */
> int preempt_count; /* 0 => preemptable,
> <0 => bug */
> mm_segment_t addr_limit; /* address limit */
> struct task_struct *task; /* main task
> structure */
>
> and current() is defined as current_thread_info()->task.
>
> Seriously, look at these beasts. Overwriting ->addr_limit is nowhere
> near
> the top threat. If attacker can overwrite thread_info, you have
> lost.
That is why THREAD_INFO_IN_TASK exists. It moves
the struct thread_info to a location away from the
stack, which means a stack overflow will not overwrite
the thread_info.
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