linux-kernel - [PATCH 5.4 044/151] KVM: x86: dont expose MSR_IA32_UMWAIT

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Message-Id: <20201117122123.570227176@linuxfoundation.org>
Date:   Tue, 17 Nov 2020 14:04:34 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Maxim Levitsky <mlevitsk@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jack Wang <jinpu.wang@...ud.ionos.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.4 044/151] KVM: x86: dont expose MSR_IA32_UMWAIT_CONTROL unconditionally

From: Maxim Levitsky <mlevitsk@...hat.com>

[ Upstream commit f4cfcd2d5aea4e96c5d483c476f3057b6b7baf6a ]

This msr is only available when the host supports WAITPKG feature.

This breaks a nested guest, if the L1 hypervisor is set to ignore
unknown msrs, because the only other safety check that the
kernel does is that it attempts to read the msr and
rejects it if it gets an exception.

Cc: stable@...r.kernel.org
Fixes: 6e3ba4abce ("KVM: vmx: Emulate MSR IA32_UMWAIT_CONTROL")
Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
Message-Id: <20200523161455.3940-3-mlevitsk@...hat.com>
Reviewed-by: Sean Christopherson <sean.j.christopherson@...el.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
(cherry picked from commit f4cfcd2d5aea4e96c5d483c476f3057b6b7baf6a
use boot_cpu_has for checking the feature)
Signed-off-by: Jack Wang <jinpu.wang@...ud.ionos.com>
Acked-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/x86/kvm/x86.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 12e83297ea020..880a24889291c 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5235,6 +5235,10 @@ static void kvm_init_msr_list(void)
 			if (!kvm_x86_ops->rdtscp_supported())
 				continue;
 			break;
+		case MSR_IA32_UMWAIT_CONTROL:
+			if (!boot_cpu_has(X86_FEATURE_WAITPKG))
+				continue;
+			break;
 		case MSR_IA32_RTIT_CTL:
 		case MSR_IA32_RTIT_STATUS:
 			if (!kvm_x86_ops->pt_supported())
-- 
2.27.0