linux-kernel - [PATCH 5.15 709/779] KVM: x86: Signal #GP, not -EPERM, on bad WRMSR(MCi

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Message-Id: <20220815180407.739335099@linuxfoundation.org>
Date:   Mon, 15 Aug 2022 20:05:53 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Sean Christopherson <seanjc@...gle.com>,
        Jim Mattson <jmattson@...gle.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.15 709/779] KVM: x86: Signal #GP, not -EPERM, on bad WRMSR(MCi_CTL/STATUS)

From: Sean Christopherson <seanjc@...gle.com>

[ Upstream commit 2368048bf5c2ec4b604ac3431564071e89a0bc71 ]

Return '1', not '-1', when handling an illegal WRMSR to a MCi_CTL or
MCi_STATUS MSR.  The behavior of "all zeros' or "all ones" for CTL MSRs
is architectural, as is the "only zeros" behavior for STATUS MSRs.  I.e.
the intent is to inject a #GP, not exit to userspace due to an unhandled
emulation case.  Returning '-1' gets interpreted as -EPERM up the stack
and effecitvely kills the guest.

Fixes: 890ca9aefa78 ("KVM: Add MCE support")
Fixes: 9ffd986c6e4e ("KVM: X86: #GP when guest attempts to write MCi_STATUS register w/o 0")
Cc: stable@...r.kernel.org
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
Reviewed-by: Jim Mattson <jmattson@...gle.com>
Link: https://lore.kernel.org/r/20220512222716.4112548-2-seanjc@google.com
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/x86/kvm/x86.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index dac2892d095c..f5b7a05530eb 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3109,13 +3109,13 @@ static int set_msr_mce(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 			 */
 			if ((offset & 0x3) == 0 &&
 			    data != 0 && (data | (1 << 10) | 1) != ~(u64)0)
-				return -1;
+				return 1;
 
 			/* MCi_STATUS */
 			if (!msr_info->host_initiated &&
 			    (offset & 0x3) == 1 && data != 0) {
 				if (!can_set_mci_status(vcpu))
-					return -1;
+					return 1;
 			}
 
 			vcpu->arch.mce_banks[offset] = data;
-- 
2.35.1