From mboxrd@z Thu Jan 1 00:00:00 1970 Reply-To: kernel-hardening@lists.openwall.com MIME-Version: 1.0 In-Reply-To: <20160616060538.GA3923@osiris> References: <20160616060538.GA3923@osiris> From: Andy Lutomirski Date: Thu, 16 Jun 2016 10:50:09 -0700 Message-ID: Content-Type: text/plain; charset=UTF-8 Subject: [kernel-hardening] Re: [PATCH 00/13] Virtually mapped stacks with guard pages (x86, core) To: Heiko Carstens Cc: Andy Lutomirski , "linux-kernel@vger.kernel.org" , X86 ML , Borislav Petkov , Nadav Amit , Kees Cook , Brian Gerst , "kernel-hardening@lists.openwall.com" , Linus Torvalds , Josh Poimboeuf List-ID: On Wed, Jun 15, 2016 at 11:05 PM, Heiko Carstens 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