[PATCH v2 05/66] KVM: x86: Check userapce CPUID array size after validating sub-leaf

Sean Christopherson
2020-03-03T00:01:58Z

Verify that the next sub-leaf of CPUID 0x4 (or 0x8000001d) is valid
before rejecting the entire KVM_GET_SUPPORTED_CPUID due to insufficent
space in the 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 the affected leafs. 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 | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 11d5f311ef10..e5cf1e0cf84a 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -552,12 +552,12 @@ static inline int __do_cpuid_func(struct kvm_cpuid_entry2 *entry, u32 function,

/* read more entries until cache_type is zero */
for (i = 1; ; ++i) {
- if (*nent >= maxnent)
- goto out;
-
cache_type = entry[i - 1].eax & 0x1f;
if (!cache_type)
break;
+
+ if (*nent >= maxnent)
+ goto out;
do_host_cpuid(&entry[i], function, i);
++*nent;
}
--
2.24.1