linux-kernel - [PATCH v7 03/12] KVM: x86/pmu: Reject userspace attempts to set reserved GLOBAL

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Message-ID: <20230603011058.1038821-4-seanjc@google.com>
Date:   Fri,  2 Jun 2023 18:10:49 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Like Xu <like.xu.linux@...il.com>,
        Like Xu <likexu@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Sandipan Das <sandipan.das@....com>
Subject: [PATCH v7 03/12] KVM: x86/pmu: Reject userspace attempts to set
 reserved GLOBAL_STATUS bits

From: Like Xu <likexu@...cent.com>

Reject userspace writes to MSR_CORE_PERF_GLOBAL_STATUS that attempt to set
reserved bits.  Allowing userspace to stuff reserved bits doesn't harm KVM
itself, but it's architecturally wrong and the guest can't clear the
unsupported bits, e.g. makes the guest's PMI handler very confused.

Signed-off-by: Like Xu <likexu@...cent.com>
[sean: rewrite changelog to avoid use of #GP, rebase on name change]
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/vmx/pmu_intel.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
index edcf8670eb4e..efd113f24c1b 100644
--- a/arch/x86/kvm/vmx/pmu_intel.c
+++ b/arch/x86/kvm/vmx/pmu_intel.c
@@ -402,6 +402,9 @@ static int intel_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		if (!msr_info->host_initiated)
 			return 1; /* RO MSR */
 
+		if (data & pmu->global_status_mask)
+			return 1;
+
 		pmu->global_status = data;
 		break;
 	case MSR_CORE_PERF_GLOBAL_CTRL:
-- 
2.41.0.rc2.161.g9c6817b8e7-goog