KVM: x86: fix out-of-bounds write in KVM_GET_EMULATED_CPUID (CVE-2019-19332)

The bounds check was present in KVM_GET_SUPPORTED_CPUID but not
KVM_GET_EMULATED_CPUID.

Reported-by: syzbot+e3f4897236c4eeb8af4f@syzkaller.appspotmail.com
Fixes: 84cffe499b94 ("kvm: Emulate MOVBE", 2013-10-29)
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 813a4d2e5c0ceaa566044642836276847d0bbc7f..cfafa320a8cf75e8437153fc36310a1f5bc3d4b3 100644 (file)
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -504,7 +504,7 @@ static inline int __do_cpuid_func(struct kvm_cpuid_entry2 *entry, u32 function,
 
        r = -E2BIG;
 
-       if (*nent >= maxnent)
+       if (WARN_ON(*nent >= maxnent))
                goto out;
 
        do_host_cpuid(entry, function, 0);
@@ -815,6 +815,9 @@ out:
 static int do_cpuid_func(struct kvm_cpuid_entry2 *entry, u32 func,
                         int *nent, int maxnent, unsigned int type)
 {
+       if (*nent >= maxnent)
+               return -E2BIG;
+
        if (type == KVM_GET_EMULATED_CPUID)
                return __do_cpuid_func_emulated(entry, func, nent, maxnent);