Date: Tue, 8 Mar 2016 13:57:40 -0800 From: Andy Lutomirski <luto@...capital.net> To: Scotty Bauer <sbauer@....utah.edu> Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, X86 ML <x86@...nel.org>, wmealing@...hat.com, Andi Kleen <ak@...ux.intel.com>, Abhiram Balasubramanian <abhiram@...utah.edu> Subject: Re: [PATCH v3 1/3] SROP Mitigation: Architecture independent code for signal cookies On Tue, Mar 8, 2016 at 1:49 PM, Scotty Bauer <sbauer@....utah.edu> wrote: > > > On 03/08/2016 01:58 PM, Andy Lutomirski wrote: >> On Tue, Mar 8, 2016 at 12:47 PM, Scott Bauer <sbauer@....utah.edu> wrote: >>> This patch adds a per-process secret to the task struct which >>> will be used during signal delivery and during a sigreturn. >>> Also, logic is added in signal.c to generate, place, extract, >>> clear and verify the signal cookie. >>> >> >> Potentially silly question: it's been a while since I read the SROP >> paper, but would the technique be effectively mitigated if sigreturn >> were to zero out the whole signal frame before returning to user mode? >> > > I don't know if I fully understand your question, but I'll respond anyway. > > SROP is possible because the kernel doesn't know whether or not the > incoming sigreturn syscall is in response from a legitimate signal that > the kernel had previously delivered and the program handled. So essentially > these patches are an attempt to give the kernel a way to verify whether or > not the the incoming sigreturn is a valid response or a exploit trying to > hijack control of the user program. > I got that part, but I thought that the interesting SROP bit was using sigreturn to return back to a frame where you could just repeat the sigreturn a bunch of times to compute things and do other evil. I'm wondering whether zeroing the whole frame would make SROP much less interesting to an attacker. --Andy
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