On Wed, Jun 15, 2016 at 11:05 PM, Heiko Carstens <heiko.carst...@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
