[PATCH 4.4 85/86] KVM: x86: Fix off-by-one error in kvm_vcpu_ioctl_x86_setup_mce

[Greg Kroah-Hartman]

From: Jim Mattson <jmattson@xxxxxxxxxx>

commit c4e0e4ab4cf3ec2b3f0b628ead108d677644ebd9 upstream.

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@xxxxxxxxxx>
Signed-off-by: Jim Mattson <jmattson@xxxxxxxxxx>
Reviewed-by: Peter Shier <pshier@xxxxxxxxxx>
Message-Id: <20200511225616.19557-1-jmattson@xxxxxxxxxx>
Reviewed-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 arch/x86/kvm/x86.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2941,7 +2941,7 @@ static int kvm_vcpu_ioctl_x86_setup_mce(
 	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;