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

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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>
This commit is contained in:
Maxim Levitsky
2021-07-19 16:05:00 +03:00
committed by Paolo Bonzini
parent 0f923e0712
commit c7dfa40099
1 changed files with 3 additions and 0 deletions
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3
arch/x86/kvm/svm/nested.c
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@ -158,6 +158,9 @@ void recalc_intercepts(struct vcpu_svm *svm)
/* If SMI is not intercepted, ignore guest SMI intercept as well */ /* If SMI is not intercepted, ignore guest SMI intercept as well */
if (!intercept_smi) if (!intercept_smi)
vmcb_clr_intercept(c, INTERCEPT_SMI); vmcb_clr_intercept(c, INTERCEPT_SMI);
vmcb_set_intercept(c, INTERCEPT_VMLOAD);
vmcb_set_intercept(c, INTERCEPT_VMSAVE);
} }
static void copy_vmcb_control_area(struct vmcb_control_area *dst, static void copy_vmcb_control_area(struct vmcb_control_area *dst,