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Message-ID: <CALCETrUTwG+fNgJQP8wYsAbxzjzARUwJ05jaRs0XfFPDHTB+ZQ@mail.gmail.com>
Date: Thu, 16 Jun 2016 10:50:09 -0700
From: Andy Lutomirski <luto@...capital.net>
To: Heiko Carstens <heiko.carstens@...ibm.com>
Cc: Andy Lutomirski <luto@...nel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
X86 ML <x86@...nel.org>, Borislav Petkov <bp@...en8.de>,
Nadav Amit <nadav.amit@...il.com>,
Kees Cook <keescook@...omium.org>,
Brian Gerst <brgerst@...il.com>,
"kernel-hardening@...ts.openwall.com"
<kernel-hardening@...ts.openwall.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH 00/13] Virtually mapped stacks with guard pages (x86, core)
On Wed, Jun 15, 2016 at 11:05 PM, Heiko Carstens
<heiko.carstens@...ibm.com> wrote:
> On Wed, Jun 15, 2016 at 05:28:22PM -0700, Andy Lutomirski wrote:
>> Since the dawn of time, a kernel stack overflow has been a real PITA
>> to debug, has caused nondeterministic crashes some time after the
>> actual overflow, and has generally been easy to exploit for root.
>>
>> With this series, arches can enable HAVE_ARCH_VMAP_STACK. Arches
>> that enable it (just x86 for now) get virtually mapped stacks with
>> guard pages. This causes reliable faults when the stack overflows.
>>
>> If the arch implements it well, we get a nice OOPS on stack overflow
>> (as opposed to panicing directly or otherwise exploding badly). On
>> x86, the OOPS is nice, has a usable call trace, and the overflowing
>> task is killed cleanly.
>
> Do you have numbers which reflect the performance impact of this change?
>
Hmm. My attempt to benchmark it caused some of the vmalloc core code
to hang. I'll dig around.
FWIW, I expect some overhead on clone/fork (if it's high, then that
would be a good reason to improve vmalloc) and a small
workload-dependent overhead due to increased TLB pressure.
--Andy
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