CVE-2021-47227

/// Technical description

In the Linux kernel, the following vulnerability has been resolved:

x86/fpu: Prevent state corruption in __fpu__restore_sig()

The non-compacted slowpath uses __copy_from_user() and copies the entire

user buffer into the kernel buffer, verbatim. This means that the kernel

buffer may now contain entirely invalid state on which XRSTOR will #GP.

validate_user_xstate_header() can detect some of that corruption, but that

leaves the onus on callers to clear the buffer.

Prior to XSAVES support, it was possible just to reinitialize the buffer,

completely, but with supervisor states that is not longer possible as the

buffer clearing code split got it backwards. Fixing that is possible but

not corrupting the state in the first place is more robust.

Avoid corruption of the kernel XSAVE buffer by using copy_user_to_xstate()

which validates the XSAVE header contents before copying the actual states

to the kernel. copy_user_to_xstate() was previously only called for

compacted-format kernel buffe

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References