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

BugLink: https://bugs.launchpad.net/bugs/1857158
commit 433f4ba1904100da65a311033f17a9bf586b287e upstream.

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>
Cc: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 803479c499e931ecf5206e6f8117a2a82063021c..dd22f8f607985d657e35f8384b5eca8df9f6de87 100644 (file)
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -405,7 +405,7 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
 
        r = -E2BIG;
 
-       if (*nent >= maxnent)
+       if (WARN_ON(*nent >= maxnent))
                goto out;
 
        do_cpuid_1_ent(entry, function, index);
@@ -707,6 +707,9 @@ 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);