In the Linux kernel, the following vulnerability has been resolved:
x86/mtrr: Check if fixed MTRRs exist before saving them
MTRRs have an obsolete fixed variant for fine grained caching control
of the 640K-1MB region that uses separate MSRs. This fixed variant has
a separate capability bit in the MTRR capability MSR.
So far all x86 CPUs which support MTRR have this separate bit set, so it
went unnoticed that mtrr_save_state() does not check the capability bit
before accessing the fixed MTRR MSRs.
Though on a CPU that does not support the fixed MTRR capability this
results in a #GP. The #GP itself is harmless because the RDMSR fault is
handled gracefully, but results in a WARN_ON().
Add the missing capability check to prevent this.
git.kernel.org/stable/c/06c1de44d378ec5439db17bf476507d68589bfe9
git.kernel.org/stable/c/34f36e6ee5bd7eff8b2adcd9fcaef369f752d82e
git.kernel.org/stable/c/388f1c954019f253a8383f7eb733f38d541e10b6
git.kernel.org/stable/c/450b6b22acdaac67a18eaf5ed498421ffcf10051
git.kernel.org/stable/c/8a90d3fc7c24608548d3a750671f9dac21d1a462
git.kernel.org/stable/c/8aa79dfb216b865e96ff890bc4ea71650f9bc8d7
git.kernel.org/stable/c/919f18f961c03d6694aa726c514184f2311a4614
git.kernel.org/stable/c/ca7d00c5656d1791e28369919e3e10febe9c3b16
security-tracker.debian.org/tracker/CVE-2024-44948