linux-kernel - [PATCH 5.5 356/367] KVM: x86: Protect exit_reason from being used in Spectre-v1/L1TF attacks

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Message-Id: <20200210122455.307475570@linuxfoundation.org>
Date:   Mon, 10 Feb 2020 04:34:29 -0800
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Marios Pomonis <pomonis@...gle.com>,
        Nick Finco <nifi@...gle.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Andrew Honig <ahonig@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.5 356/367] KVM: x86: Protect exit_reason from being used in Spectre-v1/L1TF attacks

From: Marios Pomonis <pomonis@...gle.com>

[ Upstream commit c926f2f7230b1a29e31914b51db680f8cbf3103f ]

This fixes a Spectre-v1/L1TF vulnerability in vmx_handle_exit().
While exit_reason is set by the hardware and therefore should not be
attacker-influenced, an unknown exit_reason could potentially be used to
perform such an attack.

Fixes: 55d2375e58a6 ("KVM: nVMX: Move nested code to dedicated files")

Signed-off-by: Marios Pomonis <pomonis@...gle.com>
Signed-off-by: Nick Finco <nifi@...gle.com>
Suggested-by: Sean Christopherson <sean.j.christopherson@...el.com>
Reviewed-by: Andrew Honig <ahonig@...gle.com>
Cc: stable@...r.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/x86/kvm/vmx/vmx.c | 55 +++++++++++++++++++++++-------------------
 1 file changed, 30 insertions(+), 25 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 83464a86ac405..78e01e2524bc3 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -5904,34 +5904,39 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu)
 		}
 	}
 
-	if (exit_reason < kvm_vmx_max_exit_handlers
-	    && kvm_vmx_exit_handlers[exit_reason]) {
+	if (exit_reason >= kvm_vmx_max_exit_handlers)
+		goto unexpected_vmexit;
 #ifdef CONFIG_RETPOLINE
-		if (exit_reason == EXIT_REASON_MSR_WRITE)
-			return kvm_emulate_wrmsr(vcpu);
-		else if (exit_reason == EXIT_REASON_PREEMPTION_TIMER)
-			return handle_preemption_timer(vcpu);
-		else if (exit_reason == EXIT_REASON_PENDING_INTERRUPT)
-			return handle_interrupt_window(vcpu);
-		else if (exit_reason == EXIT_REASON_EXTERNAL_INTERRUPT)
-			return handle_external_interrupt(vcpu);
-		else if (exit_reason == EXIT_REASON_HLT)
-			return kvm_emulate_halt(vcpu);
-		else if (exit_reason == EXIT_REASON_EPT_MISCONFIG)
-			return handle_ept_misconfig(vcpu);
+	if (exit_reason == EXIT_REASON_MSR_WRITE)
+		return kvm_emulate_wrmsr(vcpu);
+	else if (exit_reason == EXIT_REASON_PREEMPTION_TIMER)
+		return handle_preemption_timer(vcpu);
+	else if (exit_reason == EXIT_REASON_PENDING_INTERRUPT)
+		return handle_interrupt_window(vcpu);
+	else if (exit_reason == EXIT_REASON_EXTERNAL_INTERRUPT)
+		return handle_external_interrupt(vcpu);
+	else if (exit_reason == EXIT_REASON_HLT)
+		return kvm_emulate_halt(vcpu);
+	else if (exit_reason == EXIT_REASON_EPT_MISCONFIG)
+		return handle_ept_misconfig(vcpu);
 #endif
-		return kvm_vmx_exit_handlers[exit_reason](vcpu);
-	} else {
-		vcpu_unimpl(vcpu, "vmx: unexpected exit reason 0x%x\n",
-				exit_reason);
-		dump_vmcs();
-		vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
-		vcpu->run->internal.suberror =
+
+	exit_reason = array_index_nospec(exit_reason,
+					 kvm_vmx_max_exit_handlers);
+	if (!kvm_vmx_exit_handlers[exit_reason])
+		goto unexpected_vmexit;
+
+	return kvm_vmx_exit_handlers[exit_reason](vcpu);
+
+unexpected_vmexit:
+	vcpu_unimpl(vcpu, "vmx: unexpected exit reason 0x%x\n", exit_reason);
+	dump_vmcs();
+	vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
+	vcpu->run->internal.suberror =
 			KVM_INTERNAL_ERROR_UNEXPECTED_EXIT_REASON;
-		vcpu->run->internal.ndata = 1;
-		vcpu->run->internal.data[0] = exit_reason;
-		return 0;
-	}
+	vcpu->run->internal.ndata = 1;
+	vcpu->run->internal.data[0] = exit_reason;
+	return 0;
 }
 
 /*
-- 
2.20.1