Re: [PATCH v5 4/7] nSVM: use vmcb_save_area_cached in nested_vmcb_valid_sregs()

Maxim Levitsky
2021-11-03T17:04:17Z

On Wed, 2021-11-03 at 10:05 -0400, Emanuele Giuseppe Esposito wrote:
> Now that struct vmcb_save_area_cached contains the required
> vmcb fields values (done in nested_load_save_from_vmcb12()),
> check them to see if they are correct in nested_vmcb_valid_sregs().
>
> While at it, rename nested_vmcb_valid_sregs in nested_vmcb_check_save.
> _nested_vmcb_check_save takes the additional @save parameter, so it
> is helpful when we want to check a non-svm save state, like in
> svm_set_nested_state. The reason for that is that save is the L1
> state, not L2, so we just check it.
>
> Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
> ---
> arch/x86/kvm/svm/nested.c | 18 ++++++++++++++----
> 1 file changed, 14 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> index 162b338a6c74..64fb43234e06 100644
> --- a/arch/x86/kvm/svm/nested.c
> +++ b/arch/x86/kvm/svm/nested.c
> @@ -245,8 +245,8 @@ static bool nested_vmcb_check_controls(struct kvm_vcpu *vcpu,
> }
>
> /* Common checks that apply to both L1 and L2 state. */
> -static bool nested_vmcb_valid_sregs(struct kvm_vcpu *vcpu,
> - struct vmcb_save_area *save)
> +static bool _nested_vmcb_check_save(struct kvm_vcpu *vcpu,
> + struct vmcb_save_area_cached *save)
> {
> /*
> * FIXME: these should be done after copying the fields,
> @@ -286,6 +286,14 @@ static bool nested_vmcb_valid_sregs(struct kvm_vcpu *vcpu,
> return true;
> }
>
> +static bool nested_vmcb_check_save(struct kvm_vcpu *vcpu)
> +{
> + struct vcpu_svm *svm = to_svm(vcpu);
> + struct vmcb_save_area_cached *save = &svm->nested.save;
> +
> + return _nested_vmcb_check_save(vcpu, save);
> +}
> +
> static
> void _nested_copy_vmcb_control_to_cache(struct vmcb_control_area *to,
> struct vmcb_control_area *from)
> @@ -694,7 +702,7 @@ int nested_svm_vmrun(struct kvm_vcpu *vcpu)
> nested_copy_vmcb_control_to_cache(svm, &vmcb12->control);
> nested_copy_vmcb_save_to_cache(svm, &vmcb12->save);
>
> - if (!nested_vmcb_valid_sregs(vcpu, &vmcb12->save) ||
> + if (!nested_vmcb_check_save(vcpu) ||
> !nested_vmcb_check_controls(vcpu, &svm->nested.ctl)) {
> vmcb12->control.exit_code = SVM_EXIT_ERR;
> vmcb12->control.exit_code_hi = 0;
> @@ -1330,6 +1338,7 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
> &user_kvm_nested_state->data.svm[0];
> struct vmcb_control_area *ctl;
> struct vmcb_save_area *save;
> + struct vmcb_save_area_cached save_cached;
> unsigned long cr0;
> int ret;
>
> @@ -1397,10 +1406,11 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
> * Validate host state saved from before VMRUN (see
> * nested_svm_check_permissions).
> */

> + _nested_copy_vmcb_save_to_cache(&save_cached, save);
Nitpick: here I would probalby add a comment that we are dealing here with L1
save area and we just want to check it and not cache it.

Also suddenly the name _nested_copy_vmcb_save_to_cache sounds a bit off,
but I don't have any better idea so I don't mind leaving it as is.

Anyway,

Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>

Best regards,
Maxim Levitsky

> if (!(save->cr0 & X86_CR0_PG) ||
> !(save->cr0 & X86_CR0_PE) ||
> (save->rflags & X86_EFLAGS_VM) ||
> - !nested_vmcb_valid_sregs(vcpu, save))
> + !_nested_vmcb_check_save(vcpu, &save_cached))
> goto out_free;
>
> /*