linux-kernel - Re: [PATCH RFC v7 37/64] KVM: SVM: Add KVM_SNP

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Message-ID: <Y7BG6pSuoZsBQYrx@kernel.org>
Date:   Sat, 31 Dec 2022 14:27:54 +0000
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Michael Roth <michael.roth@....com>
Cc:     kvm@...r.kernel.org, linux-coco@...ts.linux.dev,
        linux-mm@...ck.org, linux-crypto@...r.kernel.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
        jroedel@...e.de, thomas.lendacky@....com, hpa@...or.com,
        ardb@...nel.org, pbonzini@...hat.com, seanjc@...gle.com,
        vkuznets@...hat.com, wanpengli@...cent.com, jmattson@...gle.com,
        luto@...nel.org, dave.hansen@...ux.intel.com, slp@...hat.com,
        pgonda@...gle.com, peterz@...radead.org,
        srinivas.pandruvada@...ux.intel.com, rientjes@...gle.com,
        dovmurik@...ux.ibm.com, tobin@....com, bp@...en8.de,
        vbabka@...e.cz, kirill@...temov.name, ak@...ux.intel.com,
        tony.luck@...el.com, marcorr@...gle.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com, alpergun@...gle.com,
        dgilbert@...hat.com, ashish.kalra@....com, harald@...fian.com,
        Brijesh Singh <brijesh.singh@....com>,
        Pavan Kumar Paluri <papaluri@....com>
Subject: Re: [PATCH RFC v7 37/64] KVM: SVM: Add KVM_SNP_INIT command

On Wed, Dec 14, 2022 at 01:40:29PM -0600, Michael Roth wrote:
>  static int sev_guest_init(struct kvm *kvm, struct kvm_sev_cmd *argp)
>  {
>  	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
> @@ -260,13 +279,23 @@ static int sev_guest_init(struct kvm *kvm, struct kvm_sev_cmd *argp)
>  		return ret;
>  
>  	sev->active = true;
> -	sev->es_active = argp->id == KVM_SEV_ES_INIT;
> +	sev->es_active = (argp->id == KVM_SEV_ES_INIT || argp->id == KVM_SEV_SNP_INIT);
> +	sev->snp_active = argp->id == KVM_SEV_SNP_INIT;
>  	asid = sev_asid_new(sev);
>  	if (asid < 0)
>  		goto e_no_asid;
>  	sev->asid = asid;
>  
> -	ret = sev_platform_init(&argp->error);
> +	if (sev->snp_active) {
> +		ret = verify_snp_init_flags(kvm, argp);
> +		if (ret)
> +			goto e_free;
> +
> +		ret = sev_snp_init(&argp->error, false);
> +	} else {
> +		ret = sev_platform_init(&argp->error);
> +	}

Couldn't sev_snp_init() and sev_platform_init() be called unconditionally
in order?

Since there is a hardware constraint that SNP init needs to always happen
before platform init, shouldn't SNP init happen as part of
__sev_platform_init_locked() instead?

I found these call sites for __sev_platform_init_locked(), none of which
follow the correct call order:

* sev_guest_init()
* sev_ioctl_do_pek_csr
* sev_ioctl_do_pdh_export()
* sev_ioctl_do_pek_import()
* sev_ioctl_do_pek_pdh_gen()
* sev_pci_init()

For me it looks like a bit flakky API use to have sev_snp_init() as an API
call.

I would suggest to make SNP init internal to the ccp driver and take care
of the correct orchestration over there.

Also, how it currently works in this patch set, if the firmware did not
load correctly, SNP init halts the whole system. The version check needs
to be in all call paths.

BR, Jarkko

View attachment "0001-crypto-ccp-Prevent-a-spurious-SEV_CMD_SNP_INIT-trigg.patch" of type "text/plain" (2124 bytes)