On Thu, 2017-09-21 at 11:52 -0700, Eric Biggers wrote: > From: Eric Biggers <ebigg...@google.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 <r...@redhat.com> -- All rights reversed
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