Messages in this thread | | | Subject | Re: [PATCH v3 1/3] SROP Mitigation: Architecture independent code for signal cookies | From | Scotty Bauer <> | Date | Tue, 8 Mar 2016 14:49:35 -0700 |
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On 03/08/2016 01:58 PM, Andy Lutomirski wrote: > On Tue, Mar 8, 2016 at 12:47 PM, Scott Bauer <sbauer@eng.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.
So no, zeroing out the frame wouldn't do much because if I understand your question correctly once we call sigreturn the kernel is going to hand off control to wherever the sigframe tells it to so I don't think zeroing would do much.
The reason why I zero out the cookie is so if there is a stack leak bug or something along those lines an attacker couldnt leak the cookie and try and derive what the per-process kernel secret is.
Hope that clarifies!
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