Bug 2309779 (CVE-2024-44948)

Summary: CVE-2024-44948 kernel: x86/mtrr: Check if fixed MTRRs exist before saving them
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
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Priority: medium    
Version: unspecifiedCC: dfreiber, drow, jburrell, vkumar
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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Bug Depends On: 2309898    
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Description OSIDB Bzimport 2024-09-04 19:20:31 UTC 
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.
Comment 1 Robb Gatica 2024-09-04 20:34:39 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2024090407-CVE-2024-44948-5554@gregkh/T