CVE-2024-44948

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> x86/mtrr: Check if fixed MTRRs exist before saving them<br /> <br /> MTRRs have an obsolete fixed variant for fine grained caching control<br /> of the 640K-1MB region that uses separate MSRs. This fixed variant has<br /> a separate capability bit in the MTRR capability MSR.<br /> <br /> So far all x86 CPUs which support MTRR have this separate bit set, so it<br /> went unnoticed that mtrr_save_state() does not check the capability bit<br /> before accessing the fixed MTRR MSRs.<br /> <br /> Though on a CPU that does not support the fixed MTRR capability this<br /> results in a #GP. The #GP itself is harmless because the RDMSR fault is<br /> handled gracefully, but results in a WARN_ON().<br /> <br /> Add the missing capability check to prevent this.