x86/fpu: Invalidate FPU state after a failed XRSTOR from a user buffer

Summary

In the Linux kernel, the following vulnerability has been resolved: 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. fpurestore_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 fpurestore_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 fpurestore_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".

Timeline

1. May 21, 2024, 2:19 PM UTCCVE published
2. May 21, 2024, 3:36 PM UTCCISA SSVC assessment

   Exploitation: none · Automatable: no · Technical impact: partial

3. Aug 5, 2026, 8:46 AM UTCRecord last updated

Affected versions

• Linux Linux

  Version range not reported

• Linux Linux

  5.2

References 3