CVE-2024-35801 Information

Description

In the Linux kernel the following vulnerability has been resolved:

x86/fpu: Keep xfd_state in sync with MSR_IA32_XFD

Commit 672365477ae8 (�/fpu: Update XFD state where required) and commit 8bf26758ca96 (�/fpu: Add XFD state to fpstate) introduced a per CPU variable xfd_state to keep the MSR_IA32_XFD value cached in order to avoid unnecessary writes to the MSR.

On CPU hotplug MSR_IA32_XFD is reset to the init_fpstate.xfd which wipes out any stale state. But the per CPU cached xfd value is not reset which brings them out of sync.

As a consequence a subsequent xfd_update_state() might fail to update the MSR which in turn can result in XRSTOR raising a NM in kernel space which crashes the kernel.

To fix this introduce xfd_set_state() to write xfd_state together with MSR_IA32_XFD and use it in all places that set MSR_IA32_XFD.

Reference

https://git.kernel.org/stable/c/21c7c00dae55cb0e3810d5f9506b58f68475d41d https://git.kernel.org/stable/c/1acbca933313aa866e39996904c9aca4d435c4cd https://git.kernel.org/stable/c/92b0f04e937665bde5768f3fcc622dcce44413d8 https://git.kernel.org/stable/c/b61e3b7055ac6edee4be071c52f48c26472d2624 https://git.kernel.org/stable/c/10e4b5166df9ff7a2d5316138ca668b42d004422