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Thu, 1 Oct 2026 20:27:07 +0000 Message-ID: <2b4779f4-c3d9-4b58-bc97-f31dba58fc7f@intel.com> Date: Thu, 1 Oct 2026 20:00:13 +0000 User-Agent: Mozilla Thunderbird From: "Chang S. 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>> + if (!kvm_cpu_cap_has(X86_FEATURE_APX)) >> + entry->eax = entry->ebx = entry->ecx = entry->edx = 0; >> break; > > [Severity: Medium] > Does this code leak unfiltered host CPUID capabilities for leaf 0x29 to the > guest? > > If the host supports X86_FEATURE_APX, KVM fails to apply > cpuid_entry_override(entry, CPUID_29_0_EBX) or explicitly clear the > unvirtualized registers (eax, ecx, edx) for leaf 0x29 in __do_cpuid_func(). > > This could bypass the capability mask initialized in > kvm_initialize_cpu_caps(), violating the KVM invariant that new > guest-visible features must default off and be explicitly enumerated. > This might break capability negotiation and live migration between hosts > with varying hardware support. > Leaf 0x29 currently defines only one sub-feature bit, which comes when APXF presents. Additional filtering may be necessary when more feature bits are introduced and then filtering becomes more necessary in practice. Thanks, Chang