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KVM: x86: Check for CPUID 0xD.N support before validating array size

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Now that sub-leaf 1 is handled separately, verify the next sub-leaf is
needed before rejecting KVM_GET_SUPPORTED_CPUID due to an insufficiently
sized userspace array.

Note, although this is technically a bug, it's not visible to userspace
as KVM_GET_SUPPORTED_CPUID is guaranteed to fail on KVM_CPUID_SIGNATURE,
which is hardcoded to be added after leaf 0xD.  The real motivation for
the change is to tightly couple the nent/maxnent and do_host_cpuid()
sequences in preparation for future cleanup.

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2020-03-02 15:56:10 -08:00 committed by Paolo Bonzini
parent 3dc4a9cf05
commit 1893c9415a
1 changed files with 3 additions and 2 deletions
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5
arch/x86/kvm/cpuid.c
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@ -670,13 +670,14 @@ static inline int __do_cpuid_func(struct kvm_cpuid_entry2 *entry, u32 function,
entry[1].edx = 0;
for (idx = 2, i = 2; idx < 64; ++idx) {
u64 mask = ((u64)1 << idx);
if (!(supported & BIT_ULL(idx)))
continue;
if (*nent >= maxnent)
goto out;
do_host_cpuid(&entry[i], function, idx);
if (entry[i].eax == 0 || !(supported & mask))
if (entry[i].eax == 0)
continue;
if (WARN_ON_ONCE(entry[i].ecx & 1))
continue;