Re: [PATCH RFC v8 35/56] KVM: SVM: Add KVM_SEV_SNP_LAUNCH_UPDATE command

From: Zhi Wang
Date: Fri Feb 24 2023 - 06:55:56 EST

On Mon, 20 Feb 2023 12:38:26 -0600
Michael Roth <michael.roth@xxxxxxx> wrote:

> From: Brijesh Singh <brijesh.singh@xxxxxxx>
>
> The KVM_SEV_SNP_LAUNCH_UPDATE command can be used to insert data into the
> guest's memory. The data is encrypted with the cryptographic context
> created with the KVM_SEV_SNP_LAUNCH_START.
>
> In addition to the inserting data, it can insert a two special pages
> into the guests memory: the secrets page and the CPUID page.
>
> While terminating the guest, reclaim the guest pages added in the RMP
> table. If the reclaim fails, then the page is no longer safe to be
> released back to the system and leak them.
>
> For more information see the SEV-SNP specification.
>
> Co-developed-by: Michael Roth <michael.roth@xxxxxxx>
> Signed-off-by: Michael Roth <michael.roth@xxxxxxx>
> Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
> Signed-off-by: Ashish Kalra <ashish.kalra@xxxxxxx>
> ---
> .../virt/kvm/x86/amd-memory-encryption.rst | 29 +++
> arch/x86/kvm/svm/sev.c | 190 ++++++++++++++++++
> include/uapi/linux/kvm.h | 19 ++
> 3 files changed, 238 insertions(+)
>
> diff --git a/Documentation/virt/kvm/x86/amd-memory-encryption.rst b/Documentation/virt/kvm/x86/amd-memory-encryption.rst
> index 58971fc02a15..c94be8e6d657 100644
> --- a/Documentation/virt/kvm/x86/amd-memory-encryption.rst
> +++ b/Documentation/virt/kvm/x86/amd-memory-encryption.rst
> @@ -485,6 +485,35 @@ Returns: 0 on success, -negative on error
>
> See the SEV-SNP specification for further detail on the launch input.
>
> +20. KVM_SNP_LAUNCH_UPDATE
> +-------------------------
> +
> +The KVM_SNP_LAUNCH_UPDATE is used for encrypting a memory region. It also
> +calculates a measurement of the memory contents. The measurement is a signature
> +of the memory contents that can be sent to the guest owner as an attestation
> +that the memory was encrypted correctly by the firmware.
> +
> +Parameters (in): struct kvm_snp_launch_update
> +
> +Returns: 0 on success, -negative on error
> +
> +::
> +
> + struct kvm_sev_snp_launch_update {
> + __u64 start_gfn; /* Guest page number to start from. */
> + __u64 uaddr; /* userspace address need to be encrypted */
> + __u32 len; /* length of memory region */
> + __u8 imi_page; /* 1 if memory is part of the IMI */
> + __u8 page_type; /* page type */
> + __u8 vmpl3_perms; /* VMPL3 permission mask */
> + __u8 vmpl2_perms; /* VMPL2 permission mask */
> + __u8 vmpl1_perms; /* VMPL1 permission mask */
> + };
> +
> +See the SEV-SNP spec for further details on how to build the VMPL permission
> +mask and page type.
> +
> +
> References
> ==========
>
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 097bb2138360..03dd227f6090 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -234,6 +234,37 @@ static void sev_decommission(unsigned int handle)
> sev_guest_decommission(&decommission, NULL);
> }
>
> +static int snp_page_reclaim(u64 pfn)
> +{
> + struct sev_data_snp_page_reclaim data = {0};
> + int err, rc;
> +
> + data.paddr = __sme_set(pfn << PAGE_SHIFT);
> + rc = sev_do_cmd(SEV_CMD_SNP_PAGE_RECLAIM, &data, &err);
> + if (rc) {
> + /*
> + * If the reclaim failed, then page is no longer safe
> + * to use.
> + */
> + snp_mark_pages_offline(pfn,
> + page_level_size(PG_LEVEL_4K) >> PAGE_SHIFT);
> + }
> +
> + return rc;
> +}
> +
> +static int host_rmp_make_shared(u64 pfn, enum pg_level level, bool leak)
> +{
> + int rc;
> +
> + rc = rmp_make_shared(pfn, level);
> + if (rc && leak)
> + snp_mark_pages_offline(pfn,
> + page_level_size(level) >> PAGE_SHIFT);
> +
> + return rc;
> +}
> +

PATCH 24 has similar functions. It would be better to expose them.

> static void sev_unbind_asid(struct kvm *kvm, unsigned int handle)
> {
> struct sev_data_deactivate deactivate;
> @@ -2093,6 +2124,162 @@ static int snp_launch_start(struct kvm *kvm, struct kvm_sev_cmd *argp)
> return rc;
> }
>
> +static int snp_launch_update_gfn_handler(struct kvm *kvm,
> + struct kvm_gfn_range *range,
> + void *opaque)
> +{
> + struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
> + struct kvm_memory_slot *memslot = range->slot;
> + struct sev_data_snp_launch_update data = {0};
> + struct kvm_sev_snp_launch_update params;
> + struct kvm_sev_cmd *argp = opaque;
> + int *error = &argp->error;
> + int i, n = 0, ret = 0;
> + unsigned long npages;
> + kvm_pfn_t *pfns;
> + gfn_t gfn;
> +
> + if (!kvm_slot_can_be_private(memslot)) {
> + pr_err("SEV-SNP requires restricted memory.\n");
> + return -EINVAL;
> + }
> +
> + if (copy_from_user(&params, (void __user *)(uintptr_t)argp->data, sizeof(params))) {
> + pr_err("Failed to copy user parameters for SEV-SNP launch.\n");
> + return -EFAULT;
> + }
> +
> + data.gctx_paddr = __psp_pa(sev->snp_context);
> +
> + npages = range->end - range->start;
> + pfns = kvmalloc_array(npages, sizeof(*pfns), GFP_KERNEL_ACCOUNT);
> + if (!pfns)
> + return -ENOMEM;
> +
> + pr_debug("%s: GFN range 0x%llx-0x%llx, type %d\n", __func__,
> + range->start, range->end, params.page_type);
> +
> + for (gfn = range->start, i = 0; gfn < range->end; gfn++, i++) {
> + int order, level;
> + void *kvaddr;
> +
> + ret = kvm_restrictedmem_get_pfn(memslot, gfn, &pfns[i], &order);
> + if (ret)
> + goto e_release;
> +
> + n++;
> + ret = snp_lookup_rmpentry((u64)pfns[i], &level);
> + if (ret) {
> + pr_err("Failed to ensure GFN 0x%llx is in initial shared state, ret: %d\n",
> + gfn, ret);
> + return -EFAULT;
> + }
> +
> + kvaddr = pfn_to_kaddr(pfns[i]);
> + if (!virt_addr_valid(kvaddr)) {
> + pr_err("Invalid HVA 0x%llx for GFN 0x%llx\n", (uint64_t)kvaddr, gfn);
> + ret = -EINVAL;
> + goto e_release;
> + }
> +
> + ret = kvm_read_guest_page(kvm, gfn, kvaddr, 0, PAGE_SIZE);
> + if (ret) {
> + pr_err("Guest read failed, ret: 0x%x\n", ret);
> + goto e_release;
> + }
> +
> + ret = rmp_make_private(pfns[i], gfn << PAGE_SHIFT, PG_LEVEL_4K,
> + sev_get_asid(kvm), true);
> + if (ret) {
> + ret = -EFAULT;
> + goto e_release;
> + }
> +
> + data.address = __sme_set(pfns[i] << PAGE_SHIFT);
> + data.page_size = X86_TO_RMP_PG_LEVEL(PG_LEVEL_4K);
> + data.page_type = params.page_type;
> + data.vmpl3_perms = params.vmpl3_perms;
> + data.vmpl2_perms = params.vmpl2_perms;
> + data.vmpl1_perms = params.vmpl1_perms;
> + ret = __sev_issue_cmd(argp->sev_fd, SEV_CMD_SNP_LAUNCH_UPDATE,
> + &data, error);
> + if (ret) {
> + pr_err("SEV-SNP launch update failed, ret: 0x%x, fw_error: 0x%x\n",
> + ret, *error);
> + snp_page_reclaim(pfns[i]);
> +
> + /*
> + * When invalid CPUID function entries are detected, the firmware
> + * corrects these entries for debugging purpose and leaves the
> + * page unencrypted so it can be provided users for debugging
> + * and error-reporting.
> + *
> + * Copy the corrected CPUID page back to shared memory so
> + * userpsace can retrieve this information.
> + */
> + if (params.page_type == SNP_PAGE_TYPE_CPUID &&
> + *error == SEV_RET_INVALID_PARAM) {
> + int ret;
> +
> + host_rmp_make_shared(pfns[i], PG_LEVEL_4K, true);
> +
> + ret = kvm_write_guest_page(kvm, gfn, kvaddr, 0, PAGE_SIZE);
> + if (ret)
> + pr_err("Failed to write CPUID page back to userspace, ret: 0x%x\n",
> + ret);
> + }
> +
> +
> + goto e_release;
> + }
> + }
> +
> + /*
> + * Memory attribute updates via KVM_SET_MEMORY_ATTRIBUTES are serialized
> + * via kvm->slots_lock, so use the same protocol for updating them here.
> + */
> + mutex_lock(&kvm->slots_lock);
> + kvm_vm_set_region_attr(kvm, range->start, range->end, KVM_MEMORY_ATTRIBUTE_PRIVATE);
> + mutex_unlock(&kvm->slots_lock);
> +
> +e_release:
> + /* Content of memory is updated, mark pages dirty */
> + for (i = 0; i < n; i++) {
> + set_page_dirty(pfn_to_page(pfns[i]));
> + mark_page_accessed(pfn_to_page(pfns[i]));
> +
> + /*
> + * If its an error, then update RMP entry to change page ownership
> + * to the hypervisor.
> + */
> + if (ret)
> + host_rmp_make_shared(pfns[i], PG_LEVEL_4K, true);
> +
> + put_page(pfn_to_page(pfns[i]));
> + }
> +
> + kvfree(pfns);
> + return ret;
> +}
> +
> +static int snp_launch_update(struct kvm *kvm, struct kvm_sev_cmd *argp)
> +{
> + struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
> + struct kvm_sev_snp_launch_update params;
> +
> + if (!sev_snp_guest(kvm))
> + return -ENOTTY;
> +
> + if (!sev->snp_context)
> + return -EINVAL;
> +
> + if (copy_from_user(&params, (void __user *)(uintptr_t)argp->data, sizeof(params)))
> + return -EFAULT;
> +
> + return kvm_vm_do_hva_range_op(kvm, params.uaddr, params.uaddr + params.len,
> + snp_launch_update_gfn_handler, argp);
> +}
> +
> int sev_mem_enc_ioctl(struct kvm *kvm, void __user *argp)
> {
> struct kvm_sev_cmd sev_cmd;
> @@ -2186,6 +2373,9 @@ int sev_mem_enc_ioctl(struct kvm *kvm, void __user *argp)
> case KVM_SEV_SNP_LAUNCH_START:
> r = snp_launch_start(kvm, &sev_cmd);
> break;
> + case KVM_SEV_SNP_LAUNCH_UPDATE:
> + r = snp_launch_update(kvm, &sev_cmd);
> + break;
> default:
> r = -EINVAL;
> goto out;
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index cf19799ca5ce..4098bba17aa4 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -1920,6 +1920,7 @@ enum sev_cmd_id {
> /* SNP specific commands */
> KVM_SEV_SNP_INIT,
> KVM_SEV_SNP_LAUNCH_START,
> + KVM_SEV_SNP_LAUNCH_UPDATE,
>
> KVM_SEV_NR_MAX,
> };
> @@ -2036,6 +2037,24 @@ struct kvm_sev_snp_launch_start {
> __u8 pad[6];
> };
>
> +#define KVM_SEV_SNP_PAGE_TYPE_NORMAL 0x1
> +#define KVM_SEV_SNP_PAGE_TYPE_VMSA 0x2
> +#define KVM_SEV_SNP_PAGE_TYPE_ZERO 0x3
> +#define KVM_SEV_SNP_PAGE_TYPE_UNMEASURED 0x4
> +#define KVM_SEV_SNP_PAGE_TYPE_SECRETS 0x5
> +#define KVM_SEV_SNP_PAGE_TYPE_CPUID 0x6
> +
> +struct kvm_sev_snp_launch_update {
> + __u64 start_gfn;
> + __u64 uaddr;
> + __u32 len;
> + __u8 imi_page;
> + __u8 page_type;
> + __u8 vmpl3_perms;
> + __u8 vmpl2_perms;
> + __u8 vmpl1_perms;
> +};
> +
> #define KVM_DEV_ASSIGN_ENABLE_IOMMU (1 << 0)
> #define KVM_DEV_ASSIGN_PCI_2_3 (1 << 1)
> #define KVM_DEV_ASSIGN_MASK_INTX (1 << 2)