Re: [PATCH v13 10/26] KVM: SEV: Add KVM_SEV_SNP_LAUNCH_UPDATE command

[Paolo Bonzini <pbonzini@redhat.com>]

On Thu, Apr 18, 2024 at 9:42 PM Michael Roth <michael.roth@amd.com> wrote:
>
> From: Brijesh Singh <brijesh.singh@amd.com>
>
> A key aspect of a launching an SNP guest is initializing it with a
> known/measured payload which is then encrypted into guest memory as
> pre-validated private pages and then measured into the cryptographic
> launch context created with KVM_SEV_SNP_LAUNCH_START so that the guest
> can attest itself after booting.
>
> Since all private pages are provided by guest_memfd, make use of the
> kvm_gmem_populate() interface to handle this. The general flow is that
> guest_memfd will handle allocating the pages associated with the GPA
> ranges being initialized by each particular call of
> KVM_SEV_SNP_LAUNCH_UPDATE, copying data from userspace into those pages,
> and then the post_populate callback will do the work of setting the
> RMP entries for these pages to private and issuing the SNP firmware
> calls to encrypt/measure them.
>
> For more information see the SEV-SNP specification.
>
> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
> Co-developed-by: Michael Roth <michael.roth@amd.com>
> Signed-off-by: Michael Roth <michael.roth@amd.com>
> Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
> ---
>  .../virt/kvm/x86/amd-memory-encryption.rst    |  39 ++++
>  arch/x86/include/uapi/asm/kvm.h               |  15 ++
>  arch/x86/kvm/svm/sev.c                        | 218 ++++++++++++++++++
>  3 files changed, 272 insertions(+)
>
> diff --git a/Documentation/virt/kvm/x86/amd-memory-encryption.rst b/Documentation/virt/kvm/x86/amd-memory-encryption.rst
> index 1b042f827eab..1ee8401de72d 100644
> --- a/Documentation/virt/kvm/x86/amd-memory-encryption.rst
> +++ b/Documentation/virt/kvm/x86/amd-memory-encryption.rst
> @@ -478,6 +478,45 @@ Returns: 0 on success, -negative on error
>
>  See the SEV-SNP spec [snp-fw-abi]_ for further detail on the launch input.
>
> +19. KVM_SEV_SNP_LAUNCH_UPDATE
> +-----------------------------
> +
> +The KVM_SEV_SNP_LAUNCH_UPDATE command is used for loading userspace-provided
> +data into a guest GPA range, measuring the contents into the SNP guest context
> +created by KVM_SEV_SNP_LAUNCH_START, and then encrypting/validating that GPA
> +range so that it will be immediately readable using the encryption key
> +associated with the guest context once it is booted, after which point it can
> +attest the measurement associated with its context before unlocking any
> +secrets.
> +
> +It is required that the GPA ranges initialized by this command have had the
> +KVM_MEMORY_ATTRIBUTE_PRIVATE attribute set in advance. See the documentation
> +for KVM_SET_MEMORY_ATTRIBUTES for more details on this aspect.
> +
> +Parameters (in): struct  kvm_sev_snp_launch_update
> +
> +Returns: 0 on success, -negative on error
> +
> +::
> +
> +        struct kvm_sev_snp_launch_update {
> +                __u64 gfn_start;        /* Guest page number to load/encrypt data into. */
> +                __u64 uaddr;            /* Userspace address of data to be loaded/encrypted. */
> +                __u32 len;              /* 4k-aligned length in bytes to copy into guest memory.*/
> +                __u8 type;              /* The type of the guest pages being initialized. */
> +        };
> +
> +where the allowed values for page_type are #define'd as::
> +
> +       KVM_SEV_SNP_PAGE_TYPE_NORMAL
> +       KVM_SEV_SNP_PAGE_TYPE_ZERO
> +       KVM_SEV_SNP_PAGE_TYPE_UNMEASURED
> +       KVM_SEV_SNP_PAGE_TYPE_SECRETS
> +       KVM_SEV_SNP_PAGE_TYPE_CPUID
> +
> +See the SEV-SNP spec [snp-fw-abi]_ for further details on how each page type is
> +used/measured.
> +
>  Device attribute API
>  ====================
>
> diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
> index bdf8c5461a36..8612aec97f55 100644
> --- a/arch/x86/include/uapi/asm/kvm.h
> +++ b/arch/x86/include/uapi/asm/kvm.h
> @@ -699,6 +699,7 @@ enum sev_cmd_id {
>
>         /* SNP-specific commands */
>         KVM_SEV_SNP_LAUNCH_START = 100,
> +       KVM_SEV_SNP_LAUNCH_UPDATE,
>
>         KVM_SEV_NR_MAX,
>  };
> @@ -830,6 +831,20 @@ struct kvm_sev_snp_launch_start {
>         __u8 gosvw[16];
>  };
>
> +/* Kept in sync with firmware values for simplicity. */
> +#define KVM_SEV_SNP_PAGE_TYPE_NORMAL           0x1
> +#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 gfn_start;
> +       __u64 uaddr;
> +       __u32 len;
> +       __u8 type;
> +};
> +
>  #define KVM_X2APIC_API_USE_32BIT_IDS            (1ULL << 0)
>  #define KVM_X2APIC_API_DISABLE_BROADCAST_QUIRK  (1ULL << 1)
>
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 4c5abc0e7806..e721152bae00 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -262,6 +262,35 @@ 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 (WARN_ON_ONCE(rc)) {
> +               /*
> +                * This shouldn't happen under normal circumstances, but if the
> +                * reclaim failed, then the page is no longer safe to use.
> +                */
> +               snp_leak_pages(pfn, 1);
> +       }
> +
> +       return rc;
> +}
> +
> +static int host_rmp_make_shared(u64 pfn, enum pg_level level)
> +{
> +       int rc;
> +
> +       rc = rmp_make_shared(pfn, level);
> +       if (rc)
> +               snp_leak_pages(pfn, page_level_size(level) >> PAGE_SHIFT);
> +
> +       return rc;
> +}
> +
>  static void sev_unbind_asid(struct kvm *kvm, unsigned int handle)
>  {
>         struct sev_data_deactivate deactivate;
> @@ -2131,6 +2160,192 @@ static int snp_launch_start(struct kvm *kvm, struct kvm_sev_cmd *argp)
>         return rc;
>  }
>
> +struct sev_gmem_populate_args {
> +       __u8 type;
> +       int sev_fd;
> +       int fw_error;
> +};
> +
> +static int sev_gmem_post_populate(struct kvm *kvm, gfn_t gfn_start, kvm_pfn_t pfn,
> +                                 void __user *src, int order, void *opaque)
> +{
> +       struct sev_gmem_populate_args *sev_populate_args = opaque;
> +       struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
> +       int n_private = 0, ret, i;
> +       int npages = (1 << order);
> +       gfn_t gfn;
> +
> +       pr_debug("%s: gfn_start %llx pfn_start %llx npages %d\n",
> +                __func__, gfn_start, pfn, npages);
> +
> +       for (gfn = gfn_start, i = 0; gfn < gfn_start + npages; gfn++, i++) {
> +               struct sev_data_snp_launch_update fw_args = {0};
> +               bool assigned;
> +               void *vaddr;
> +               int level;
> +
> +               if (!kvm_mem_is_private(kvm, gfn)) {
> +                       pr_debug("%s: Failed to ensure GFN 0x%llx has private memory attribute set\n",
> +                                __func__, gfn);
> +                       ret = -EINVAL;
> +                       break;
> +               }
> +
> +               ret = snp_lookup_rmpentry((u64)pfn + i, &assigned, &level);
> +               if (ret || assigned) {
> +                       pr_debug("%s: Failed to ensure GFN 0x%llx RMP entry is initial shared state, ret: %d assigned: %d\n",
> +                                __func__, gfn, ret, assigned);
> +                       ret = -EINVAL;
> +                       break;
> +               }
> +
> +               vaddr = kmap_local_pfn(pfn + i);
> +               ret = copy_from_user(vaddr, src + i * PAGE_SIZE, PAGE_SIZE);
> +               if (ret) {
> +                       pr_debug("Failed to copy source page into GFN 0x%llx\n", gfn);
> +                       goto out_unmap;
> +               }
> +
> +               ret = rmp_make_private(pfn + i, gfn << PAGE_SHIFT, PG_LEVEL_4K,
> +                                      sev_get_asid(kvm), true);
> +               if (ret) {
> +                       pr_debug("%s: Failed to convert GFN 0x%llx to private, ret: %d\n",
> +                                __func__, gfn, ret);
> +                       goto out_unmap;
> +               }
> +
> +               n_private++;
> +
> +               fw_args.gctx_paddr = __psp_pa(sev->snp_context);
> +               fw_args.address = __sme_set(pfn_to_hpa(pfn + i));
> +               fw_args.page_size = PG_LEVEL_TO_RMP(PG_LEVEL_4K);
> +               fw_args.page_type = sev_populate_args->type;
> +               ret = __sev_issue_cmd(sev_populate_args->sev_fd, SEV_CMD_SNP_LAUNCH_UPDATE,
> +                                     &fw_args, &sev_populate_args->fw_error);
> +               if (ret) {
> +                       pr_debug("%s: SEV-SNP launch update failed, ret: 0x%x, fw_error: 0x%x\n",
> +                                __func__, ret, sev_populate_args->fw_error);
> +
> +                       if (snp_page_reclaim(pfn + i))
> +                               goto out_unmap;
> +
> +                       /*
> +                        * When invalid CPUID function entries are detected,
> +                        * firmware writes the expected values into the page and
> +                        * leaves it unencrypted so it can be used for debugging
> +                        * and error-reporting.
> +                        *
> +                        * Copy this page back into the source buffer so
> +                        * userspace can use this information to provide
> +                        * information on which CPUID leaves/fields failed CPUID
> +                        * validation.
> +                        */
> +                       if (sev_populate_args->type == KVM_SEV_SNP_PAGE_TYPE_CPUID &&
> +                           sev_populate_args->fw_error == SEV_RET_INVALID_PARAM) {
> +                               host_rmp_make_shared(pfn + i, PG_LEVEL_4K);
> +
> +                               if (copy_to_user(src + i * PAGE_SIZE,
> +                                                vaddr, PAGE_SIZE))
> +                                       pr_debug("Failed to write CPUID page back to userspace\n");
> +                       }
> +               }
> +
> +out_unmap:
> +               kunmap_local(vaddr);
> +               if (ret)
> +                       break;
> +       }
> +
> +       if (ret) {
> +               pr_debug("%s: exiting with error ret %d, undoing %d populated gmem pages.\n",
> +                        __func__, ret, n_private);
> +               for (i = 0; i < n_private; i++)
> +                       host_rmp_make_shared(pfn + i, PG_LEVEL_4K);
> +       }
> +
> +       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 sev_gmem_populate_args sev_populate_args = {0};
> +       struct kvm_sev_snp_launch_update params;
> +       struct kvm_memory_slot *memslot;
> +       unsigned int npages;
> +       int ret = 0;
> +
> +       if (!sev_snp_guest(kvm) || !sev->snp_context)
> +               return -EINVAL;
> +
> +       if (copy_from_user(&params, u64_to_user_ptr(argp->data), sizeof(params)))
> +               return -EFAULT;
> +
> +       if (!IS_ALIGNED(params.len, PAGE_SIZE) ||
> +           (params.type != KVM_SEV_SNP_PAGE_TYPE_NORMAL &&
> +            params.type != KVM_SEV_SNP_PAGE_TYPE_ZERO &&
> +            params.type != KVM_SEV_SNP_PAGE_TYPE_UNMEASURED &&
> +            params.type != KVM_SEV_SNP_PAGE_TYPE_SECRETS &&
> +            params.type != KVM_SEV_SNP_PAGE_TYPE_CPUID))
> +               return -EINVAL;
> +
> +       npages = params.len / PAGE_SIZE;
> +
> +       pr_debug("%s: GFN range 0x%llx-0x%llx type %d\n", __func__,
> +                params.gfn_start, params.gfn_start + npages, params.type);
> +
> +       /*
> +        * For each GFN that's being prepared as part of the initial guest
> +        * state, the following pre-conditions are verified:
> +        *
> +        *   1) The backing memslot is a valid private memslot.
> +        *   2) The GFN has been set to private via KVM_SET_MEMORY_ATTRIBUTES
> +        *      beforehand.
> +        *   3) The PFN of the guest_memfd has not already been set to private
> +        *      in the RMP table.
> +        *
> +        * The KVM MMU relies on kvm->mmu_invalidate_seq to retry nested page
> +        * faults if there's a race between a fault and an attribute update via
> +        * KVM_SET_MEMORY_ATTRIBUTES, and a similar approach could be utilized
> +        * here. However, kvm->slots_lock guards against both this as well as
> +        * concurrent memslot updates occurring while these checks are being
> +        * performed, so use that here to make it easier to reason about the
> +        * initial expected state and better guard against unexpected
> +        * situations.
> +        */
> +       mutex_lock(&kvm->slots_lock);
> +
> +       memslot = gfn_to_memslot(kvm, params.gfn_start);
> +       if (!kvm_slot_can_be_private(memslot)) {
> +               ret = -EINVAL;
> +               goto out;
> +       }
> +
> +       sev_populate_args.sev_fd = argp->sev_fd;
> +       sev_populate_args.type = params.type;
> +
> +       ret = kvm_gmem_populate(kvm, params.gfn_start, u64_to_user_ptr(params.uaddr),
> +                               npages, sev_gmem_post_populate, &sev_populate_args);
> +       if (ret < 0) {
> +               argp->error = sev_populate_args.fw_error;
> +               pr_debug("%s: kvm_gmem_populate failed, ret %d (fw_error %d)\n",
> +                        __func__, ret, argp->error);
> +       } else if (ret < npages) {
> +               params.len = ret * PAGE_SIZE;
> +               ret = -EINTR;

This probably should 1) update also gfn_start and uaddr 2) return 0
for consistency with the planned KVM_PRE_FAULT_MEMORY ioctl (aka
KVM_MAP_MEMORY).

Paolo