CVE-2021-47226 x86/fpu: Invalidate FPU state after a failed XRSTOR from a user buffer

What is CVE-2021-47226?

CVE-2021-47226 is a high-severity vulnerability in Linux kernel, published on 21 May 2024. It can only be exploited from the same machine or local network, with no action from the victim.

Official description

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.

__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".

Weakness: CWE-203

Which versions are affected by CVE-2021-47226?

It affects 1 product.

Products include Linux kernel.

How do I fix CVE-2021-47226?

Apply the vendor's patch.

Is CVE-2021-47226 being exploited?

There is no known exploitation of CVE-2021-47226 in the wild and no public exploit code.

Other vulnerabilities in Linux kernel

• CVE-2026-53266 Linux Kernel Out-of-Bounds Write Exploited High 8.8
• CVE-2013-6282 Linux Kernel Improper Input Validation Exploited High 8.8
• CVE-2022-0185 Linux Kernel Heap-Based Buffer Overflow Exploited High 8.4
• CVE-2013-2094 Linux Kernel Privilege Escalation Exploited High 8.4
• CVE-2026-53362 Linux Kernel Unspecified Exploited High 7.8

All Linux kernel vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as DEBIAN-CVE-2021-47226, GHSA-4jxh-jrgp-4422, UBUNTU-CVE-2021-47226.