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

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>

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index fc85405963860079a333bb99972a721ebca156be..fd9b29aa7abc03d890ab27617e18c9729614ebe0 100644 (file)
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -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;