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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Jue Wang <juew@google.com>,
        Jim Mattson <jmattson@google.com>,
        Peter Shier <pshier@google.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Paolo Bonzini <pbonzini@redhat.com>
Subject: [PATCH 4.9 89/90] KVM: x86: Fix off-by-one error in kvm_vcpu_ioctl_x86_setup_mce
Date:   Mon, 18 May 2020 19:37:07 +0200
Message-Id: <20200518173509.157337939@linuxfoundation.org>
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From: Jim Mattson <jmattson@google.com>

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@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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 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
@@ -3128,7 +3128,7 @@ 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;