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KVM: nSVM: always intercept VMLOAD/VMSAVE when nested (CVE-2021-3656)

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commit c7dfa4009965a9b2d7b329ee970eb8da0d32f0bc upstream.

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: 89c8a4984f ("KVM: SVM: Enable Virtual VMLOAD VMSAVE feature")

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Maxim Levitsky 2021-07-19 16:05:00 +03:00 • committed by Greg Kroah-Hartman
commit a17f2f2c89
1 changed files with 3 additions and 0 deletions
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3
arch/x86/kvm/svm.c
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@ -516,6 +516,9 @@ 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)