linux-kernel - [PATCH] KVM: x86/cpuid: Exclude unpermitted xfeatures for vcpu->arch.guest_supported

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Date:   Sun, 23 Jan 2022 13:50:25 +0800
From:   Like Xu <like.xu.linux@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Jing Liu <jing2.liu@...el.com>, Wanpeng Li <wanpengli@...cent.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Jim Mattson <jmattson@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] KVM: x86/cpuid: Exclude unpermitted xfeatures for vcpu->arch.guest_supported_xcr0

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

A malicious user space can bypass xstate_get_guest_group_perm() in the
KVM_GET_SUPPORTED_CPUID mechanism and obtain unpermitted xfeatures,
since the validity check of xcr0 depends only on guest_supported_xcr0.

Fixes: 445ecdf79be0 ("kvm: x86: Exclude unpermitted xfeatures at KVM_GET_SUPPORTED_CPUID")
Signed-off-by: Like Xu <likexu@...cent.com>
---
 arch/x86/kvm/cpuid.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 3902c28fb6cb..1bd4d560cbdd 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -266,7 +266,8 @@ static void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 		vcpu->arch.guest_supported_xcr0 = 0;
 	else
 		vcpu->arch.guest_supported_xcr0 =
-			(best->eax | ((u64)best->edx << 32)) & supported_xcr0;
+			(best->eax | ((u64)best->edx << 32)) &
+			(supported_xcr0 & xstate_get_guest_group_perm());
 
 	/*
 	 * Bits 127:0 of the allowed SECS.ATTRIBUTES (CPUID.0x12.0x1) enumerate
-- 
2.33.1