On 01/04/21 16:18, Maxim Levitsky wrote:
While KVM's MMU should be fully reset by loading of nested CR0/CR3/CR4
by KVM_SET_SREGS, we are not in nested mode yet when we do it and therefore
only root_mmu is reset.
On regular nested entries we call nested_svm_load_cr3 which both updates
the guest's CR3 in the MMU when it is needed, and it also initializes
the mmu again which makes it initialize the walk_mmu as well when nested
paging is enabled in both host and guest.
Since we don't call nested_svm_load_cr3 on nested state load,
the walk_mmu can be left uninitialized, which can lead to a NULL pointer
dereference while accessing it if we happen to get a nested page fault
right after entering the nested guest first time after the migration and
we decide to emulate it, which leads to the emulator trying to access
walk_mmu->gva_to_gpa which is NULL.
Therefore we should call this function on nested state load as well.
Suggested-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
---
arch/x86/kvm/svm/nested.c | 40 +++++++++++++++++++++------------------
1 file changed, 22 insertions(+), 18 deletions(-)
diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 8523f60adb92..ac5e3e17bda4 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -215,24 +215,6 @@ static bool nested_svm_vmrun_msrpm(struct vcpu_svm *svm)
return true;
}
-static bool svm_get_nested_state_pages(struct kvm_vcpu *vcpu)
-{
- struct vcpu_svm *svm = to_svm(vcpu);
-
- if (WARN_ON(!is_guest_mode(vcpu)))
- return true;
-
- if (!nested_svm_vmrun_msrpm(svm)) {
- vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
- vcpu->run->internal.suberror =
- KVM_INTERNAL_ERROR_EMULATION;
- vcpu->run->internal.ndata = 0;
- return false;
- }
-
- return true;
-}
-
static bool nested_vmcb_check_controls(struct vmcb_control_area *control)
{
if (CC(!vmcb_is_intercept(control, INTERCEPT_VMRUN)))
@@ -1312,6 +1294,28 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
return ret;
}
+static bool svm_get_nested_state_pages(struct kvm_vcpu *vcpu)
+{
+ struct vcpu_svm *svm = to_svm(vcpu);
+
+ if (WARN_ON(!is_guest_mode(vcpu)))
+ return true;
+
+ if (nested_svm_load_cr3(&svm->vcpu, vcpu->arch.cr3,
+ nested_npt_enabled(svm)))
+ return false;
+
+ if (!nested_svm_vmrun_msrpm(svm)) {
+ vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
+ vcpu->run->internal.suberror =
+ KVM_INTERNAL_ERROR_EMULATION;
+ vcpu->run->internal.ndata = 0;
+ return false;
+ }
+
+ return true;
+}
+
struct kvm_x86_nested_ops svm_nested_ops = {
.check_events = svm_check_nested_events,
.triple_fault = nested_svm_triple_fault,
Reviewed-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
