[SRU OEM-5.13 2/2] KVM: nSVM: always intercept VMLOAD/VMSAVE when nested (CVE-2021-3656)

Thadeu Lima de Souza Cascardo cascardo at canonical.com
Tue Aug 17 13:00:21 UTC 2021

From: Maxim Levitsky <mlevitsk at redhat.com>

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 at redhat.com>
Signed-off-by: Maxim Levitsky <mlevitsk at redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini at redhat.com>
(backported from commit c7dfa4009965a9b2d7b329ee970eb8da0d32f0bc)
[cascardo: context adjustment]
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo at canonical.com>
 arch/x86/kvm/svm/nested.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 7f3b55561ae8..61f418644235 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -149,6 +149,9 @@ void recalc_intercepts(struct vcpu_svm *svm)
 	for (i = 0; i < MAX_INTERCEPT; i++)
 		c->intercepts[i] |= g->intercepts[i];
+	vmcb_set_intercept(c, INTERCEPT_VMLOAD);
+	vmcb_set_intercept(c, INTERCEPT_VMSAVE);
 static void copy_vmcb_control_area(struct vmcb_control_area *dst,

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