linux-kernel - Re: [PATCH RFC v7 38/64] KVM: SVM: Add KVM_SEV_SNP_LAUNCH

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Date:   Wed, 15 Mar 2023 07:50:47 -0600
From:   Peter Gonda <pgonda@...gle.com>
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,
        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, jarkko@...nel.org, ashish.kalra@....com,
        harald@...fian.com, Brijesh Singh <brijesh.singh@....com>,
        Josh Eads <josheads@...gle.com>
Subject: Re: [PATCH RFC v7 38/64] KVM: SVM: Add KVM_SEV_SNP_LAUNCH_START command

>
> +/*
> + * The guest context contains all the information, keys and metadata
> + * associated with the guest that the firmware tracks to implement SEV
> + * and SNP features. The firmware stores the guest context in hypervisor
> + * provide page via the SNP_GCTX_CREATE command.
> + */
> +static void *snp_context_create(struct kvm *kvm, struct kvm_sev_cmd *argp)
> +{
> +       struct sev_data_snp_addr data = {};
> +       void *context;
> +       int rc;
> +
> +       /* Allocate memory for context page */
> +       context = snp_alloc_firmware_page(GFP_KERNEL_ACCOUNT);
> +       if (!context)
> +               return NULL;
> +
> +       data.gctx_paddr = __psp_pa(context);
> +       rc = __sev_issue_cmd(argp->sev_fd, SEV_CMD_SNP_GCTX_CREATE, &data, &argp->error);
> +       if (rc) {
> +               snp_free_firmware_page(context);
> +               return NULL;
> +       }
> +
> +       return context;
> +}
> +
> +static int snp_bind_asid(struct kvm *kvm, int *error)
> +{
> +       struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
> +       struct sev_data_snp_activate data = {0};
> +
> +       data.gctx_paddr = __psp_pa(sev->snp_context);
> +       data.asid   = sev_get_asid(kvm);
> +       return sev_issue_cmd(kvm, SEV_CMD_SNP_ACTIVATE, &data, error);
> +}
> +
> +static int snp_launch_start(struct kvm *kvm, struct kvm_sev_cmd *argp)
> +{
> +       struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
> +       struct sev_data_snp_launch_start start = {0};
> +       struct kvm_sev_snp_launch_start params;
> +       int rc;
> +
> +       if (!sev_snp_guest(kvm))
> +               return -ENOTTY;
> +
> +       if (copy_from_user(&params, (void __user *)(uintptr_t)argp->data, sizeof(params)))
> +               return -EFAULT;
> +
> +       sev->snp_context = snp_context_create(kvm, argp);
> +       if (!sev->snp_context)
> +               return -ENOTTY;

This was reported-by josheads@. Its possible that userspace can
repeatedly call snp_launch_start() causing the leak of memory from
repeated snp_context_create() calls, leaking SNP contexts in the ASP,
and leaking ASIDs.

A possible solution could be to just error out if snp_context already exists?


+       if (sev->snp_context)
+               return -EINVAL;
+



> +
> +       start.gctx_paddr = __psp_pa(sev->snp_context);
> +       start.policy = params.policy;
> +       memcpy(start.gosvw, params.gosvw, sizeof(params.gosvw));
> +       rc = __sev_issue_cmd(argp->sev_fd, SEV_CMD_SNP_LAUNCH_START, &start, &argp->error);
> +       if (rc)
> +               goto e_free_context;
> +
> +       sev->fd = argp->sev_fd;
> +       rc = snp_bind_asid(kvm, &argp->error);
> +       if (rc)
> +               goto e_free_context;
> +
> +       return 0;
> +
> +e_free_context:
> +       snp_decommission_context(kvm);
> +
> +       return rc;
> +}
> +