If a nested run isn't pending, snapshot vmcs01.GUEST_BNDCFGS irrespective of whether or not VM_ENTRY_LOAD_BNDCFGS is set in vmcs12. When restoring nested state, e.g. after migration, without a nested run pending, prepare_vmcs02() will propagate nested.vmcs01_guest_bndcfgs to vmcs02, i.e. will load garbage/zeros into vmcs02.GUEST_BNDCFGS. If userspace restores nested state before MSRs, then loading garbage is a non-issue as loading BNDCFGS will also update vmcs02. But if usersepace restores MSRs first, then KVM is responsible for propagating L2's value, which is actually thrown into vmcs01, into vmcs02. Restoring L2 MSRs into vmcs01, i.e. loading all MSRs before nested state is all kinds of bizarre and ideally would not be supported. Sadly, some VMMs do exactly that and rely on KVM to make things work. Note, there's still a lurking SMM bug, as propagating vmcs01.GUEST_BNDFGS to vmcs02 across RSM may corrupt L2's BNDCFGS. But KVM's entire VMX+SMM emulation is flawed as SMI+RSM should not toouch _any_ VMCS when use the "default treatment of SMIs", i.e. when not using an SMI Transfer Monitor. Link: https://lore.kernel.org/all/Yobt1XwOfb5M6Dfa@xxxxxxxxxx Fixes: 62cf9bd8118c ("KVM: nVMX: Fix emulation of VM_ENTRY_LOAD_BNDCFGS") Cc: stable@xxxxxxxxxxxxxxx Cc: Lei Wang <lei4.wang@xxxxxxxxx> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx> --- arch/x86/kvm/vmx/nested.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c index 7d8cd0ebcc75..66c25bb56938 100644 --- a/arch/x86/kvm/vmx/nested.c +++ b/arch/x86/kvm/vmx/nested.c @@ -3382,7 +3382,8 @@ enum nvmx_vmentry_status nested_vmx_enter_non_root_mode(struct kvm_vcpu *vcpu, if (!(vmcs12->vm_entry_controls & VM_ENTRY_LOAD_DEBUG_CONTROLS)) vmx->nested.vmcs01_debugctl = vmcs_read64(GUEST_IA32_DEBUGCTL); if (kvm_mpx_supported() && - !(vmcs12->vm_entry_controls & VM_ENTRY_LOAD_BNDCFGS)) + (!vmx->nested.nested_run_pending || + !(vmcs12->vm_entry_controls & VM_ENTRY_LOAD_BNDCFGS))) vmx->nested.vmcs01_guest_bndcfgs = vmcs_read64(GUEST_BNDCFGS); /* -- 2.36.1.476.g0c4daa206d-goog
