x86/fpu: Invalidate FPU state after a failed XRSTOR from a user buffer
Both Intel and AMD consider it to be architecturally valid for XRSTOR to fail with #PF but nonetheless change the register state. The actual conditions under which this might occur are unclear [1], but it seems plausible that this might be triggered if one sibling thread unmaps a page and invalidates the shared TLB while another sibling thread is executing XRSTOR on the page in question. __fpu__restore_sig() can execute XRSTOR while the hardware registers are preserved on behalf of a different victim task (using the fpu_fpregs_owner_ctx mechanism), and, in theory, XRSTOR could fail but modify the registers. If this happens, then there is a window in which __fpu__restore_sig() could schedule out and the victim task could schedule back in without reloading its own FPU registers. This would result in part of the FPU state that __fpu__restore_sig() was attempting to load leaking into the victim task's user-visible state. Invalidate preserved FPU registers on XRSTOR failure to prevent this situation from corrupting any state. [1] Frequent readers of the errata lists might imagine "complex microarchitectural conditions". Fixes: 1d731e73 ("x86/fpu: Add a fastpath to __fpu__restore_sig()") Signed-off-by:Andy Lutomirski <luto@kernel.org> Signed-off-by:
Thomas Gleixner <tglx@linutronix.de> Signed-off-by:
Borislav Petkov <bp@suse.de> Acked-by:
Dave Hansen <dave.hansen@linux.intel.com> Acked-by:
Rik van Riel <riel@surriel.com> Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/20210608144345.758116583@linutronix.de
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