KVM: x86: Fix off-by-one error in kvm_vcpu_ioctl_x86_setup_mce

Bank_num is a one-based count of banks, not a zero-based index. It
overflows the allocated space only when strictly greater than
KVM_MAX_MCE_BANKS.

Fixes: a9e38c3e01ad ("KVM: x86: Catch potential overrun in MCE setup")
Signed-off-by: Jue Wang <juew@google.com>
Signed-off-by: Jim Mattson <jmattson@google.com>
Reviewed-by: Peter Shier <pshier@google.com>
Message-Id: <20200511225616.19557-1-jmattson@google.com>
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index d11eba8b85c63b3eeba51e88f40defa9e0a9dd98..c17e6eb9ad43d84fece0aeb875bfd903e69a252c 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3759,7 +3759,7 @@ static int kvm_vcpu_ioctl_x86_setup_mce(struct kvm_vcpu *vcpu,
        unsigned bank_num = mcg_cap & 0xff, bank;
 
        r = -EINVAL;
-       if (!bank_num || bank_num >= KVM_MAX_MCE_BANKS)
+       if (!bank_num || bank_num > KVM_MAX_MCE_BANKS)
                goto out;
        if (mcg_cap & ~(kvm_mce_cap_supported | 0xff | 0xff0000))
                goto out;