[PATCH v2 07/66] KVM: x86: Check for CPUID 0xD.N support before validating array size

Sean Christopherson
2020-03-03T00:00:51Z

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>
---
arch/x86/kvm/cpuid.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index fc8540596386..fd9b29aa7abc 100644
--- 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;
--
2.24.1