linux-kernel - [PATCH 4.14 31/64] KVM: nSVM: always intercept VMLOAD/VMSAVE when nested (CVE-2021-3656)

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Message-Id: <20210824170457.710623-32-sashal@kernel.org>
Date:   Tue, 24 Aug 2021 13:04:24 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Maxim Levitsky <mlevitsk@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: [PATCH 4.14 31/64] KVM: nSVM: always intercept VMLOAD/VMSAVE when nested (CVE-2021-3656)

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

[ upstream commit c7dfa4009965a9b2d7b329ee970eb8da0d32f0bc ]

If L1 disables VMLOAD/VMSAVE intercepts, and doesn't enable
Virtual VMLOAD/VMSAVE (currently not supported for the nested hypervisor),
then VMLOAD/VMSAVE must operate on the L1 physical memory, which is only
possible by making L0 intercept these instructions.

Failure to do so allowed the nested guest to run VMLOAD/VMSAVE unintercepted,
and thus read/write portions of the host physical memory.

Fixes: 89c8a4984fc9 ("KVM: SVM: Enable Virtual VMLOAD VMSAVE feature")

Suggested-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/x86/kvm/svm.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 3571253b8690..0e6e158b8f8f 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -389,6 +389,9 @@ static void recalc_intercepts(struct vcpu_svm *svm)
 	c->intercept_dr = h->intercept_dr | g->intercept_dr;
 	c->intercept_exceptions = h->intercept_exceptions | g->intercept_exceptions;
 	c->intercept = h->intercept | g->intercept;
+
+	c->intercept |= (1ULL << INTERCEPT_VMLOAD);
+	c->intercept |= (1ULL << INTERCEPT_VMSAVE);
 }
 
 static inline struct vmcb *get_host_vmcb(struct vcpu_svm *svm)
-- 
2.30.2