linux-kernel - Re: [PATCH 2/2] KVM: VMX: Inject #GP, not #UD, if SGX2 ENCLS leafs are unsupported

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Date:   Thu, 6 Apr 2023 09:17:54 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>
CC:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "binbin.wu@...ux.intel.com" <binbin.wu@...ux.intel.com>
Subject: Re: [PATCH 2/2] KVM: VMX: Inject #GP, not #UD, if SGX2 ENCLS leafs
 are unsupported

On Wed, 2023-04-05 at 16:45 -0700, Sean Christopherson wrote:
> Per Intel's SDM, unsupported ENCLS leafs result in a #GP, not a #UD.
> SGX1 is a special snowflake as the SGX1 flag is used by the CPU as a
> "soft" disable, e.g. if software disables machine check reporting, i.e.
> having SGX but not SGX1 is effectively "SGX completely unsupported" and
> and thus #UDs.

If I recall correctly, this is an erratum which can clear SGX1 in CPUID while
the SGX flag is still in CPUID?

But I am not sure whether this part is relevant to this patch?  Because SDM
already says ENCLS causes #UD if SGX1 isn't present.  This patch changes
"unsupported leaf" from causing #UD to causing #GP, which is also documented in
SDM.

> 
> Fixes: 9798adbc04cf ("KVM: VMX: Frame in ENCLS handler for SGX virtualization")
> Cc: Binbin Wu <binbin.wu@...ux.intel.com>
> Cc: Kai Huang <kai.huang@...el.com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/kvm/vmx/sgx.c | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx/sgx.c b/arch/x86/kvm/vmx/sgx.c
> index f881f6ff6408..1c092ab89c33 100644
> --- a/arch/x86/kvm/vmx/sgx.c
> +++ b/arch/x86/kvm/vmx/sgx.c
> @@ -350,11 +350,12 @@ static int handle_encls_einit(struct kvm_vcpu *vcpu)
>  
>  static inline bool encls_leaf_enabled_in_guest(struct kvm_vcpu *vcpu, u32 leaf)
>  {
> -	if (!enable_sgx || !guest_cpuid_has(vcpu, X86_FEATURE_SGX))
> -		return false;
> -
> +	/*
> +	 * ENCLS #UDs if SGX1 isn't supported, i.e. this point will be reached

Why #UDs instead of #UD?  Is #UD a verb?

> +	 * if and only if the SGX1 leafs are enabled.
> +	 */

Is it better to move "ENCLS #UDs if SGX1 isn't supported" part to ...

>  	if (leaf >= ECREATE && leaf <= ETRACK)
> -		return guest_cpuid_has(vcpu, X86_FEATURE_SGX1);
> +		return true;
>  
>  	if (leaf >= EAUG && leaf <= EMODT)
>  		return guest_cpuid_has(vcpu, X86_FEATURE_SGX2);
> @@ -373,9 +374,11 @@ int handle_encls(struct kvm_vcpu *vcpu)
>  {
>  	u32 leaf = (u32)kvm_rax_read(vcpu);
>  
> -	if (!encls_leaf_enabled_in_guest(vcpu, leaf)) {
> +	if (!enable_sgx || !guest_cpuid_has(vcpu, X86_FEATURE_SGX) ||
> +	    !guest_cpuid_has(vcpu, X86_FEATURE_SGX1)) {
>  		kvm_queue_exception(vcpu, UD_VECTOR);

... above here, where the actual code reside?

> -	} else if (!sgx_enabled_in_guest_bios(vcpu) || !is_paging(vcpu)) {
> +	} else if (!encls_leaf_enabled_in_guest(vcpu, leaf) ||
> +		   !sgx_enabled_in_guest_bios(vcpu) || !is_paging(vcpu)) {
>  		kvm_inject_gp(vcpu, 0);
>  	} else {
>  		if (leaf == ECREATE)
> -- 
> 2.40.0.348.gf938b09366-goog
>