KVM: x86: Harden copying of userspace-array against overflow

cpuid.c utilizes vmemdup_user() and array_size() to copy two userspace
arrays. This, currently, does not check for an overflow.

Use the new wrapper vmemdup_array_user() to copy the arrays more safely,
as vmemdup_user() doesn't check for overflow.

Note, KVM explicitly checks the number of entries before duplicating the
array, i.e. adding the overflow check should be a glorified nop.

Suggested-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Philipp Stanner <pstanner@redhat.com>
Link: https://lore.kernel.org/r/20231102181526.43279-2-pstanner@redhat.com
[sean: call out that KVM pre-checks the number of entries]
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: Philipp Stanner

arch/x86/kvm/cpuid.c

@@ -469,7 +469,7 @@ int kvm_vcpu_ioctl_set_cpuid(struct kvm_vcpu *vcpu,
 		return -E2BIG;
 
 	if (cpuid->nent) {
-		e = vmemdup_user(entries, array_size(sizeof(*e), cpuid->nent));
+		e = vmemdup_array_user(entries, cpuid->nent, sizeof(*e));
 		if (IS_ERR(e))
 			return PTR_ERR(e);
 
@@ -513,7 +513,7 @@ int kvm_vcpu_ioctl_set_cpuid2(struct kvm_vcpu *vcpu,
 		return -E2BIG;
 
 	if (cpuid->nent) {
-		e2 = vmemdup_user(entries, array_size(sizeof(*e2), cpuid->nent));
+		e2 = vmemdup_array_user(entries, cpuid->nent, sizeof(*e2));
 		if (IS_ERR(e2))
 			return PTR_ERR(e2);
 	}