On Fri, Aug 20, 2021 at 10:00 AM Brijesh Singh <brijesh.singh@xxxxxxx> wrote:
>
> 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.
>
> Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
> ---
> .../virt/kvm/amd-memory-encryption.rst | 29 +++
> arch/x86/kvm/svm/sev.c | 187 ++++++++++++++++++
> include/uapi/linux/kvm.h | 19 ++
> 3 files changed, 235 insertions(+)
>
> diff --git a/Documentation/virt/kvm/amd-memory-encryption.rst b/Documentation/virt/kvm/amd-memory-encryption.rst
> index 937af3447954..ddcd94e9ffed 100644
> --- a/Documentation/virt/kvm/amd-memory-encryption.rst
> +++ b/Documentation/virt/kvm/amd-memory-encryption.rst
> @@ -478,6 +478,35 @@ 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 dbf04a52b23d..4b126598b7aa 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -17,6 +17,7 @@
> #include <linux/misc_cgroup.h>
> #include <linux/processor.h>
> #include <linux/trace_events.h>
> +#include <linux/sev.h>
> #include <asm/fpu/internal.h>
>
> #include <asm/pkru.h>
> @@ -227,6 +228,49 @@ static void sev_decommission(unsigned int handle)
> sev_guest_decommission(&decommission, NULL);
> }
>
> +static inline void snp_leak_pages(u64 pfn, enum pg_level level)
> +{
> + unsigned int npages = page_level_size(level) >> PAGE_SHIFT;
> +
> + WARN(1, "psc failed pfn 0x%llx pages %d (leaking)\n", pfn, npages);
> +
> + while (npages) {
> + memory_failure(pfn, 0);
> + dump_rmpentry(pfn);
> + npages--;
> + pfn++;
> + }
> +}
> +
> +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 = snp_guest_page_reclaim(&data, &err);
> + if (rc) {
> + /*
> + * If the reclaim failed, then page is no longer safe
> + * to use.
> + */
> + snp_leak_pages(pfn, PG_LEVEL_4K);
> + }
> +
> + 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_leak_pages(pfn, level);
> +
> + return rc;
> +}
> +
> static void sev_unbind_asid(struct kvm *kvm, unsigned int handle)
> {
> struct sev_data_deactivate deactivate;
> @@ -1620,6 +1664,123 @@ static int snp_launch_start(struct kvm *kvm, struct kvm_sev_cmd *argp)
> return rc;
> }
>
> +static bool is_hva_registered(struct kvm *kvm, hva_t hva, size_t len)
> +{
> + struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
> + struct list_head *head = &sev->regions_list;
> + struct enc_region *i;
> +
> + lockdep_assert_held(&kvm->lock);
> +
> + list_for_each_entry(i, head, list) {
> + u64 start = i->uaddr;
> + u64 end = start + i->size;
> +
> + if (start <= hva && end >= (hva + len))
> + return true;
> + }
> +
> + return false;
> +}
Internally we actually register the guest memory in chunks for various
reasons. So for our largest SEV VM we have 768 1 GB entries in
|sev->regions_list|. This was OK before because no look ups were done.
Now that we are performing a look ups a linked list with linear time
lookups seems not ideal, could we switch the back data structure here
to something more conducive too fast lookups?
> +
> +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_data_snp_launch_update data = {0};
> + struct kvm_sev_snp_launch_update params;
> + unsigned long npages, pfn, n = 0;
Could we have a slightly more descriptive name for |n|? nprivate
maybe? Also why not zero in the loop below?
for (i = 0, n = 0; i < npages; ++i)
> + int *error = &argp->error;
> + struct page **inpages;
> + int ret, i, level;
Should |i| be an unsigned long since it can is tracked in a for loop
with "i < npages" npages being an unsigned long? (|n| too)
> + u64 gfn;
> +
> + if (!sev_snp_guest(kvm))
> + return -ENOTTY;
> +
> + if (!sev->snp_context)
> + return -EINVAL;
> +
> + if (copy_from_user(¶ms, (void __user *)(uintptr_t)argp->data, sizeof(params)))
> + return -EFAULT;
> +
> + /* Verify that the specified address range is registered. */
> + if (!is_hva_registered(kvm, params.uaddr, params.len))
> + return -EINVAL;
> +
> + /*
> + * The userspace memory is already locked so technically we don't
> + * need to lock it again. Later part of the function needs to know
> + * pfn so call the sev_pin_memory() so that we can get the list of
> + * pages to iterate through.
> + */
> + inpages = sev_pin_memory(kvm, params.uaddr, params.len, &npages, 1);
> + if (!inpages)
> + return -ENOMEM;
> +
> + /*
> + * Verify that all the pages are marked shared in the RMP table before
> + * going further. This is avoid the cases where the userspace may try
This is *too* avoid cases...
> + * updating the same page twice.
> + */
> + for (i = 0; i < npages; i++) {
> + if (snp_lookup_rmpentry(page_to_pfn(inpages[i]), &level) != 0) {
> + sev_unpin_memory(kvm, inpages, npages);
> + return -EFAULT;
> + }
> + }
> +
> + gfn = params.start_gfn;
> + level = PG_LEVEL_4K;
> + data.gctx_paddr = __psp_pa(sev->snp_context);
> +
> + for (i = 0; i < npages; i++) {
> + pfn = page_to_pfn(inpages[i]);
> +
> + ret = rmp_make_private(pfn, gfn << PAGE_SHIFT, level, sev_get_asid(kvm), true);
> + if (ret) {
> + ret = -EFAULT;
> + goto e_unpin;
> + }
> +
> + n++;
> + data.address = __sme_page_pa(inpages[i]);
> + data.page_size = X86_TO_RMP_PG_LEVEL(level);
> + 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) {
> + /*
> + * If the command failed then need to reclaim the page.
> + */
> + snp_page_reclaim(pfn);
> + goto e_unpin;
> + }
Hmm if this call fails after the first iteration of this loop it will
lead to a hard to reproduce LaunchDigest right? Say if we are
SnpLaunchUpdating just 2 pages A and B. If we first call this ioctl
and A is SNP_LAUNCH_UPDATED'd but B fails, we then make A shared again
in the RMP. So we must call the ioctl with 2 pages again, after fixing
the issue with page B. Now the Launch digest has something like
Hash(A) then HASH(A & B) right (overly simplified) so A will be
included twice right? I am not sure if anything better can be done
here but might be worth documenting IIUC.
> +
> + gfn++;
> + }
> +
> +e_unpin:
> + /* Content of memory is updated, mark pages dirty */
> + for (i = 0; i < n; i++) {
> + set_page_dirty_lock(inpages[i]);
> + mark_page_accessed(inpages[i]);
> +
> + /*
> + * If its an error, then update RMP entry to change page ownership
> + * to the hypervisor.
> + */
> + if (ret)
> + host_rmp_make_shared(pfn, level, true);
> + }
> +
> + /* Unlock the user pages */
> + sev_unpin_memory(kvm, inpages, npages);
> +
> + return ret;
> +}
> +
> int svm_mem_enc_op(struct kvm *kvm, void __user *argp)
> {
> struct kvm_sev_cmd sev_cmd;
> @@ -1712,6 +1873,9 @@ int svm_mem_enc_op(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;
> @@ -1794,6 +1958,29 @@ find_enc_region(struct kvm *kvm, struct kvm_enc_region *range)
> static void __unregister_enc_region_locked(struct kvm *kvm,
> struct enc_region *region)
> {
> + unsigned long i, pfn;
> + int level;
> +
> + /*
> + * The guest memory pages are assigned in the RMP table. Unassign it
> + * before releasing the memory.
> + */
> + if (sev_snp_guest(kvm)) {
> + for (i = 0; i < region->npages; i++) {
> + pfn = page_to_pfn(region->pages[i]);
> +
> + if (!snp_lookup_rmpentry(pfn, &level))
> + continue;
> +
> + cond_resched();
> +
> + if (level > PG_LEVEL_4K)
> + pfn &= ~(KVM_PAGES_PER_HPAGE(PG_LEVEL_2M) - 1);
> +
> + host_rmp_make_shared(pfn, level, true);
> + }
> + }
> +
> sev_unpin_memory(kvm, region->pages, region->npages);
> list_del(®ion->list);
> kfree(region);
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index e6416e58cd9a..0681be4bdfdf 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -1715,6 +1715,7 @@ 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,
> };
> @@ -1831,6 +1832,24 @@ 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)
> --
> 2.17.1
>
>
