linux-kernel - Re: [PATCH v5 4/7] nSVM: use vmcb_save_area_cached in nested_vmcb_valid

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Date:   Wed, 03 Nov 2021 19:03:54 +0200
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Emanuele Giuseppe Esposito <eesposit@...hat.com>,
        kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 4/7] nSVM: use vmcb_save_area_cached in
 nested_vmcb_valid_sregs()

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@...hat.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@...hat.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;
>  
>  	/*