[PATCH 3.16 62/72] KVM: x86: fix out-of-bounds write in KVM_GET_EMULATED_CPUID (CVE-2019-19332)

[Ben Hutchings]

3.16.79-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Paolo Bonzini <pbonzini@xxxxxxxxxx>

commit 433f4ba1904100da65a311033f17a9bf586b287e upstream.

The bounds check was present in KVM_GET_SUPPORTED_CPUID but not
KVM_GET_EMULATED_CPUID.

Reported-by: syzbot+e3f4897236c4eeb8af4f@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 84cffe499b94 ("kvm: Emulate MOVBE", 2013-10-29)
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 arch/x86/kvm/cpuid.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -327,7 +327,7 @@ static inline int __do_cpuid_ent(struct
 
 	r = -E2BIG;
 
-	if (*nent >= maxnent)
+	if (WARN_ON(*nent >= maxnent))
 		goto out;
 
 	do_cpuid_1_ent(entry, function, index);
@@ -599,6 +599,9 @@ out:
 static int do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 func,
 			u32 idx, int *nent, int maxnent, unsigned int type)
 {
+	if (*nent >= maxnent)
+		return -E2BIG;
+
 	if (type == KVM_GET_EMULATED_CPUID)
 		return __do_cpuid_ent_emulated(entry, func, idx, nent, maxnent);