Messages in this thread | | | From | Andy Lutomirski <> | Date | Thu, 16 Jun 2016 10:50:09 -0700 | Subject | Re: [PATCH 00/13] Virtually mapped stacks with guard pages (x86, core) |
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On Wed, Jun 15, 2016 at 11:05 PM, Heiko Carstens <heiko.carstens@de.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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