Date: Thu, 21 Sep 2017 16:41:29 -0400 From: Rik van Riel <riel@...hat.com> To: Eric Biggers <ebiggers3@...il.com>, x86@...nel.org Cc: linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com, Andy Lutomirski <luto@...nel.org>, Dave Hansen <dave.hansen@...ux.intel.com>, Dmitry Vyukov <dvyukov@...gle.com>, Fenghua Yu <fenghua.yu@...el.com>, Ingo Molnar <mingo@...nel.org>, Kevin Hao <haokexin@...il.com>, Oleg Nesterov <oleg@...hat.com>, Wanpeng Li <wanpeng.li@...mail.com>, Yu-cheng Yu <yu-cheng.yu@...el.com>, Michael Halcrow <mhalcrow@...gle.com>, Eric Biggers <ebiggers@...gle.com> Subject: Re: [PATCH v3 3/3] x86/fpu: reinitialize FPU registers if restoring FPU state fails On Thu, 2017-09-21 at 11:52 -0700, Eric Biggers wrote: > From: Eric Biggers <ebiggers@...gle.com> > > Userspace can change the FPU state of a task using the ptrace() or > rt_sigreturn() system calls. Because reserved bits in the FPU state > can > cause the XRSTOR instruction to fail, the kernel has to carefully > validate that no reserved bits or other invalid values are being set. > > Unfortunately, there have been bugs in this validation code. For > example, we were not checking that the 'xcomp_bv' field in the > xstate_header was 0. As-is, such bugs are exploitable to read the > FPU > registers of other processes on the system. To do so, an attacker > can > create a task, assign to it an invalid FPU state, then spin in a loop > and monitor the values of the FPU registers. Because the task's FPU > registers are not being restored, sometimes the FPU registers will > have > the values from another process. > Reviewed-by: Rik van Riel <riel@...hat.com> -- All rights reversed Download attachment "signature.asc" of type "application/pgp-signature" (474 bytes)
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