[PATCH v2 53/66] KVM: x86: Do kvm_cpuid_array capacity checks in terminal functions

[Sean Christopherson]

Perform the capacity checks on the userspace provided kvm_cpuid_array
in the lower __do_cpuid_func() and __do_cpuid_func_emulated().
Pre-checking the array in do_cpuid_func() no longer adds value now that
__do_cpuid_func() has been trimmed down to size, i.e. doesn't invoke a
big pile of retpolined functions before doing anything useful.

Note, __do_cpuid_func() already checks the array capacity via
do_host_cpuid(), "moving" the check to __do_cpuid_func() simply means
removing a WARN_ON().

Suggested-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
---
 arch/x86/kvm/cpuid.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index eebd7f613f67..f879fcbd6fb2 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -478,8 +478,12 @@ static struct kvm_cpuid_entry2 *do_host_cpuid(struct kvm_cpuid_array *array,
 
 static int __do_cpuid_func_emulated(struct kvm_cpuid_array *array, u32 func)
 {
-	struct kvm_cpuid_entry2 *entry = &array->entries[array->nent];
+	struct kvm_cpuid_entry2 *entry;
 
+	if (array->nent >= array->maxnent)
+		return -E2BIG;
+
+	entry = &array->entries[array->nent];
 	entry->function = func;
 	entry->index = 0;
 	entry->flags = 0;
@@ -516,7 +520,7 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
 	r = -E2BIG;
 
 	entry = do_host_cpuid(array, function, 0);
-	if (WARN_ON(!entry))
+	if (!entry)
 		goto out;
 
 	switch (function) {
@@ -787,9 +791,6 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
 static int do_cpuid_func(struct kvm_cpuid_array *array, u32 func,
 			 unsigned int type)
 {
-	if (array->nent >= array->maxnent)
-		return -E2BIG;
-
 	if (type == KVM_GET_EMULATED_CPUID)
 		return __do_cpuid_func_emulated(array, func);
 
-- 
2.24.1