Date: Tue, 29 Mar 2016 13:53:23 -0600 From: Scott Bauer <sbauer@....utah.edu> To: linux-kernel@...r.kernel.org Cc: kernel-hardening@...ts.openwall.com, x86@...nel.org, ak@...ux.intel.com, luto@...capital.net, mingo@...hat.com, tglx@...utronix.de, wmealing@...hat.com, torvalds@...ux-foundation.org Subject: [PATCH v4 0/4] SROP Mitigation: Sigreturn Cookies 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. Version changes: v3->v4 Removed ambiguous __user annotation, added Documentation and test code. v2->v3 Changed cookie calculation from using restored regs->sp to using frame pointer from before restoration. v1->v2 Miscellaneous nits and code cleanup. Scott Bauer (4): SROP Mitigation: Architecture independent code for signal cookies x86: SROP Mitigation: Implement Signal Cookies Sysctl: SROP Mitigation: Add Sysctl argument to disable SROP. Documentation: SROP Mitigation: Add documentation for SROP cookies Documentation/security/srop-cookies.txt | 203 ++++++++++++++++++++++++++++++++ arch/x86/ia32/ia32_signal.c | 65 +++++++++- arch/x86/include/asm/fpu/signal.h | 2 + arch/x86/kernel/fpu/signal.c | 10 ++ arch/x86/kernel/signal.c | 83 +++++++++++-- fs/exec.c | 3 + include/linux/sched.h | 7 ++ include/linux/signal.h | 3 + kernel/signal.c | 49 ++++++++ kernel/sysctl.c | 8 ++ 10 files changed, 418 insertions(+), 15 deletions(-)
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