Date: Tue, 29 Mar 2016 15:36:49 -0600 From: Scotty Bauer <sbauer@....utah.edu> To: Andy Lutomirski <luto@...capital.net> 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>, Andi Kleen <ak@...ux.intel.com>, Ingo Molnar <mingo@...hat.com>, Thomas Gleixner <tglx@...utronix.de>, wmealing@...hat.com, Linus Torvalds <torvalds@...ux-foundation.org> Subject: Re: [PATCH v4 0/4] SROP Mitigation: Sigreturn Cookies On 03/29/2016 03:29 PM, Andy Lutomirski wrote: > On Tue, Mar 29, 2016 at 12:53 PM, Scott Bauer <sbauer@....utah.edu> wrote: >> Sigreturn-oriented programming is a new attack vector in userland >> where an attacker crafts a fake signal frame on the stack and calls >> sigreturn. The kernel will extract the fake signal frame, which >> contains attacker controlled "saved" registers. The kernel will then >> transfer control to the attacker controlled userland instruction pointer. >> >> To prevent SROP attacks the kernel needs to know or be able to dervive >> whether a sigreturn it is processing is in response to a legitimate >> signal the kernel previously delivered. >> >> Further information and test code can be found in Documentation/security >> and this excellent article: >> http://lwn.net/Articles/676803/ >> >> These patches implement the necessary changes to generate a cookie >> which will be placed above signal frame upon signal delivery to userland. >> The cookie is generated using a per-process random value xor'd with >> the address where the cookie will be stored on the stack. >> >> Upon a sigreturn the kernel will extract the cookie from userland, >> recalculate what the original cookie should be and verify that the two >> do not differ. If the two differ the kernel will terminate the process >> with a SIGSEGV. >> >> This prevents SROP by adding a value that the attacker cannot guess, >> but the kernel can verify. Therefore an attacker cannot use sigreturn as >> a method to control the flow of a process. >> > > Has anyone verified that this doesn't break CRIU cross-machine (or > cross-boot) migration and that this doesn't break dosemu? You're > changing the ABI here. > I haven't yet I'll do that to verify it breaks -- I'm pretty sure under some conditions it will break CRIU. That's why we added the sysctl to turn it off. Should I have mentioned this in the main commit that it possibly breaks CRIU/DOSEMU? I went ahead and added that to the Documentation.
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