Re: [PATCH RFC v7 29/64] crypto: ccp: Handle the legacy SEV command when SNP is enabled

["Kalra, Ashish" <ashish.kalra@amd.com>]

Hello Alper,

On 1/12/2023 2:47 PM, Alper Gun wrote:
> On Wed, Dec 14, 2022 at 11:54 AM Michael Roth <michael.roth@amd.com> wrote:
>>
>> From: Brijesh Singh <brijesh.singh@amd.com>
>>
>> The behavior of the SEV-legacy commands is altered when the SNP firmware
>> is in the INIT state. When SNP is in INIT state, all the SEV-legacy
>> commands that cause the firmware to write to memory must be in the
>> firmware state before issuing the command..
>>
>> A command buffer may contains a system physical address that the firmware
>> may write to. There are two cases that need to be handled:
>>
>> 1) system physical address points to a guest memory
>> 2) system physical address points to a host memory
>>
>> To handle the case #1, change the page state to the firmware in the RMP
>> table before issuing the command and restore the state to shared after the
>> command completes.
>>
>> For the case #2, use a bounce buffer to complete the request.
>>
>> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
>> Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
>> Signed-off-by: Michael Roth <michael.roth@amd.com>
>> ---
>>   drivers/crypto/ccp/sev-dev.c | 370 ++++++++++++++++++++++++++++++++++-
>>   drivers/crypto/ccp/sev-dev.h |  12 ++
>>   2 files changed, 372 insertions(+), 10 deletions(-)
>>
>> diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
>> index 4c12e98a1219..5eb2e8f364d4 100644
>> --- a/drivers/crypto/ccp/sev-dev.c
>> +++ b/drivers/crypto/ccp/sev-dev.c
>> @@ -286,6 +286,30 @@ static int rmp_mark_pages_firmware(unsigned long paddr, unsigned int npages, boo
>>          return rc;
>>   }
>>
>> +static int rmp_mark_pages_shared(unsigned long paddr, unsigned int npages)
>> +{
>> +       /* Cbit maybe set in the paddr */
>> +       unsigned long pfn = __sme_clr(paddr) >> PAGE_SHIFT;
>> +       int rc, n = 0, i;
>> +
>> +       for (i = 0; i < npages; i++, pfn++, n++) {
>> +               rc = rmp_make_shared(pfn, PG_LEVEL_4K);
>> +               if (rc)
>> +                       goto cleanup;
>> +       }
>> +
>> +       return 0;
>> +
>> +cleanup:
>> +       /*
>> +        * If failed to change the page state to shared, then its not safe
>> +        * to release the page back to the system, leak it.
>> +        */
>> +       snp_mark_pages_offline(pfn, npages - n);
>> +
>> +       return rc;
>> +}
>> +
>>   static struct page *__snp_alloc_firmware_pages(gfp_t gfp_mask, int order, bool locked)
>>   {
>>          unsigned long npages = 1ul << order, paddr;
>> @@ -487,12 +511,295 @@ static int sev_write_init_ex_file_if_required(int cmd_id)
>>          return sev_write_init_ex_file();
>>   }
>>
>> +static int alloc_snp_host_map(struct sev_device *sev)
>> +{
>> +       struct page *page;
>> +       int i;
>> +
>> +       for (i = 0; i < MAX_SNP_HOST_MAP_BUFS; i++) {
>> +               struct snp_host_map *map = &sev->snp_host_map[i];
>> +
>> +               memset(map, 0, sizeof(*map));
>> +
>> +               page = alloc_pages(GFP_KERNEL_ACCOUNT, get_order(SEV_FW_BLOB_MAX_SIZE));
>> +               if (!page)
>> +                       return -ENOMEM;
>> +
>> +               map->host = page_address(page);
>> +       }
>> +
>> +       return 0;
>> +}
>> +
>> +static void free_snp_host_map(struct sev_device *sev)
>> +{
>> +       int i;
>> +
>> +       for (i = 0; i < MAX_SNP_HOST_MAP_BUFS; i++) {
>> +               struct snp_host_map *map = &sev->snp_host_map[i];
>> +
>> +               if (map->host) {
>> +                       __free_pages(virt_to_page(map->host), get_order(SEV_FW_BLOB_MAX_SIZE));
>> +                       memset(map, 0, sizeof(*map));
>> +               }
>> +       }
>> +}
>> +
>> +static int map_firmware_writeable(u64 *paddr, u32 len, bool guest, struct snp_host_map *map)
>> +{
>> +       unsigned int npages = PAGE_ALIGN(len) >> PAGE_SHIFT;
>> +
>> +       map->active = false;
>> +
>> +       if (!paddr || !len)
>> +               return 0;
>> +
>> +       map->paddr = *paddr;
>> +       map->len = len;
>> +
>> +       /* If paddr points to a guest memory then change the page state to firmwware. */
>> +       if (guest) {
>> +               if (rmp_mark_pages_firmware(*paddr, npages, true))
>> +                       return -EFAULT;
>> +
>> +               goto done;
>> +       }
>> +
>> +       if (!map->host)
>> +               return -ENOMEM;
>> +
>> +       /* Check if the pre-allocated buffer can be used to fullfil the request. */
>> +       if (len > SEV_FW_BLOB_MAX_SIZE)
>> +               return -EINVAL;
>> +
>> +       /* Transition the pre-allocated buffer to the firmware state. */
>> +       if (rmp_mark_pages_firmware(__pa(map->host), npages, true))
>> +               return -EFAULT;
>> +
>> +       /* Set the paddr to use pre-allocated firmware buffer */
>> +       *paddr = __psp_pa(map->host);
>> +
>> +done:
>> +       map->active = true;
>> +       return 0;
>> +}
>> +
>> +static int unmap_firmware_writeable(u64 *paddr, u32 len, bool guest, struct snp_host_map *map)
>> +{
>> +       unsigned int npages = PAGE_ALIGN(len) >> PAGE_SHIFT;
>> +
>> +       if (!map->active)
>> +               return 0;
>> +
>> +       /* If paddr points to a guest memory then restore the page state to hypervisor. */
>> +       if (guest) {
>> +               if (snp_reclaim_pages(*paddr, npages, true))
>> +                       return -EFAULT;
>> +
>> +               goto done;
>> +       }
>> +
>> +       /*
>> +        * Transition the pre-allocated buffer to hypervisor state before the access.
>> +        *
>> +        * This is because while changing the page state to firmware, the kernel unmaps
>> +        * the pages from the direct map, and to restore the direct map the pages must
>> +        * be transitioned back to the shared state.
>> +        */
>> +       if (snp_reclaim_pages(__pa(map->host), npages, true))
>> +               return -EFAULT;
>> +
>> +       /* Copy the response data firmware buffer to the callers buffer. */
>> +       memcpy(__va(__sme_clr(map->paddr)), map->host, min_t(size_t, len, map->len));
>> +       *paddr = map->paddr;
>> +
>> +done:
>> +       map->active = false;
>> +       return 0;
>> +}
>> +
>> +static bool sev_legacy_cmd_buf_writable(int cmd)
>> +{
>> +       switch (cmd) {
>> +       case SEV_CMD_PLATFORM_STATUS:
>> +       case SEV_CMD_GUEST_STATUS:
>> +       case SEV_CMD_LAUNCH_START:
>> +       case SEV_CMD_RECEIVE_START:
>> +       case SEV_CMD_LAUNCH_MEASURE:
>> +       case SEV_CMD_SEND_START:
>> +       case SEV_CMD_SEND_UPDATE_DATA:
>> +       case SEV_CMD_SEND_UPDATE_VMSA:
>> +       case SEV_CMD_PEK_CSR:
>> +       case SEV_CMD_PDH_CERT_EXPORT:
>> +       case SEV_CMD_GET_ID:
>> +       case SEV_CMD_ATTESTATION_REPORT:
>> +               return true;
>> +       default:
>> +               return false;
>> +       }
>> +}
>> +
>> +#define prep_buffer(name, addr, len, guest, map) \
>> +       func(&((typeof(name *))cmd_buf)->addr, ((typeof(name *))cmd_buf)->len, guest, map)
>> +
>> +static int __snp_cmd_buf_copy(int cmd, void *cmd_buf, bool to_fw, int fw_err)
>> +{
>> +       int (*func)(u64 *paddr, u32 len, bool guest, struct snp_host_map *map);
>> +       struct sev_device *sev = psp_master->sev_data;
>> +       bool from_fw = !to_fw;
>> +
>> +       /*
>> +        * After the command is completed, change the command buffer memory to
>> +        * hypervisor state.
>> +        *
>> +        * The immutable bit is automatically cleared by the firmware, so
>> +        * no not need to reclaim the page.
>> +        */
>> +       if (from_fw && sev_legacy_cmd_buf_writable(cmd)) {
>> +               if (rmp_mark_pages_shared(__pa(cmd_buf), 1))
>> +                       return -EFAULT;
> 
> If we return here, we will skip calling unmap_firmware_writeable and
> we will leak some pages in firmware state.

Do you mean those (guest) pages which were transitioned to firmware 
state as part of 
snp_aware_copy_to_firmware()->_snp_cmd_buf_copy()->map_firmware_writeable()?

> 
>> +
>> +               /* No need to go further if firmware failed to execute command. */
>> +               if (fw_err)
>> +                       return 0;
>> +       }
>> +
>> +       if (to_fw)
>> +               func = map_firmware_writeable;
>> +       else
>> +               func = unmap_firmware_writeable;
>> +
>> +       /*
>> +        * A command buffer may contains a system physical address. If the address
>> +        * points to a host memory then use an intermediate firmware page otherwise
>> +        * change the page state in the RMP table.
>> +        */
>> +       switch (cmd) {
>> +       case SEV_CMD_PDH_CERT_EXPORT:
>> +               if (prep_buffer(struct sev_data_pdh_cert_export, pdh_cert_address,
>> +                               pdh_cert_len, false, &sev->snp_host_map[0]))
>> +                       goto err;
>> +               if (prep_buffer(struct sev_data_pdh_cert_export, cert_chain_address,
>> +                               cert_chain_len, false, &sev->snp_host_map[1]))
>> +                       goto err;
>> +               break;
>> +       case SEV_CMD_GET_ID:
>> +               if (prep_buffer(struct sev_data_get_id, address, len,
>> +                               false, &sev->snp_host_map[0]))
>> +                       goto err;
>> +               break;
>> +       case SEV_CMD_PEK_CSR:
>> +               if (prep_buffer(struct sev_data_pek_csr, address, len,
>> +                               false, &sev->snp_host_map[0]))
>> +                       goto err;
>> +               break;
>> +       case SEV_CMD_LAUNCH_UPDATE_DATA:
>> +               if (prep_buffer(struct sev_data_launch_update_data, address, len,
>> +                               true, &sev->snp_host_map[0]))
>> +                       goto err;
>> +               break;
>> +       case SEV_CMD_LAUNCH_UPDATE_VMSA:
>> +               if (prep_buffer(struct sev_data_launch_update_vmsa, address, len,
>> +                               true, &sev->snp_host_map[0]))
>> +                       goto err;
>> +               break;
>> +       case SEV_CMD_LAUNCH_MEASURE:
>> +               if (prep_buffer(struct sev_data_launch_measure, address, len,
>> +                               false, &sev->snp_host_map[0]))
>> +                       goto err;
>> +               break;
>> +       case SEV_CMD_LAUNCH_UPDATE_SECRET:
>> +               if (prep_buffer(struct sev_data_launch_secret, guest_address, guest_len,
>> +                               true, &sev->snp_host_map[0]))
>> +                       goto err;
>> +               break;
>> +       case SEV_CMD_DBG_DECRYPT:
>> +               if (prep_buffer(struct sev_data_dbg, dst_addr, len, false,
>> +                               &sev->snp_host_map[0]))
>> +                       goto err;
>> +               break;
>> +       case SEV_CMD_DBG_ENCRYPT:
>> +               if (prep_buffer(struct sev_data_dbg, dst_addr, len, true,
>> +                               &sev->snp_host_map[0]))
>> +                       goto err;
>> +               break;
>> +       case SEV_CMD_ATTESTATION_REPORT:
>> +               if (prep_buffer(struct sev_data_attestation_report, address, len,
>> +                               false, &sev->snp_host_map[0]))
>> +                       goto err;
>> +               break;
>> +       case SEV_CMD_SEND_START:
>> +               if (prep_buffer(struct sev_data_send_start, session_address,
>> +                               session_len, false, &sev->snp_host_map[0]))
>> +                       goto err;
>> +               break;
>> +       case SEV_CMD_SEND_UPDATE_DATA:
>> +               if (prep_buffer(struct sev_data_send_update_data, hdr_address, hdr_len,
>> +                               false, &sev->snp_host_map[0]))
>> +                       goto err;
>> +               if (prep_buffer(struct sev_data_send_update_data, trans_address,
>> +                               trans_len, false, &sev->snp_host_map[1]))
>> +                       goto err;
>> +               break;
>> +       case SEV_CMD_SEND_UPDATE_VMSA:
>> +               if (prep_buffer(struct sev_data_send_update_vmsa, hdr_address, hdr_len,
>> +                               false, &sev->snp_host_map[0]))
>> +                       goto err;
>> +               if (prep_buffer(struct sev_data_send_update_vmsa, trans_address,
>> +                               trans_len, false, &sev->snp_host_map[1]))
>> +                       goto err;
>> +               break;
>> +       case SEV_CMD_RECEIVE_UPDATE_DATA:
>> +               if (prep_buffer(struct sev_data_receive_update_data, guest_address,
>> +                               guest_len, true, &sev->snp_host_map[0]))
>> +                       goto err;
>> +               break;
>> +       case SEV_CMD_RECEIVE_UPDATE_VMSA:
>> +               if (prep_buffer(struct sev_data_receive_update_vmsa, guest_address,
>> +                               guest_len, true, &sev->snp_host_map[0]))
>> +                       goto err;
>> +               break;
>> +       default:
>> +               break;
>> +       }
>> +
>> +       /* The command buffer need to be in the firmware state. */
>> +       if (to_fw && sev_legacy_cmd_buf_writable(cmd)) {
>> +               if (rmp_mark_pages_firmware(__pa(cmd_buf), 1, true))
>> +                       return -EFAULT;
> 
> This function moves two separate pages to firmware state. First
> calling map_firmware_writeable and second calling
> rmp_mark_pages_firmware for cmd_buf.
> In case rmp_mark_pages_firmware fails for cmd_buf, the page which has
> already moved to firmware state in map_firmware_writeable should be
> reclaimed.
> This is a problem especially if we leak a guest owned page in firmware
> state. Since this is used only by legacy SEV VMs, these leaked pages
> will never be reclaimed back when destroying these VMs.
> 

Yes, this looks to be an inherent issue with the original patch, as you 
mentioned there are two pages - guest owned page and the HV cmd_buf, and 
failure to transition the cmd_buf back to HV/shared state has no 
corresponding recovery/reclaim for the transitioned guest page.

Thanks,
Ashish

>>
>> +       }
>> +
>> +       return 0;
>> +
>> +err:
>> +       return -EINVAL;
>> +}
>> +
>> +static inline bool need_firmware_copy(int cmd)
>> +{
>> +       struct sev_device *sev = psp_master->sev_data;
>> +
>> +       /* After SNP is INIT'ed, the behavior of legacy SEV command is changed. */
>> +       return ((cmd < SEV_CMD_SNP_INIT) && sev->snp_initialized) ? true : false;
>> +}
>> +
>> +static int snp_aware_copy_to_firmware(int cmd, void *data)
>> +{
>> +       return __snp_cmd_buf_copy(cmd, data, true, 0);
>> +}
>> +
>> +static int snp_aware_copy_from_firmware(int cmd, void *data, int fw_err)
>> +{
>> +       return __snp_cmd_buf_copy(cmd, data, false, fw_err);
>> +}
>> +
>>   static int __sev_do_cmd_locked(int cmd, void *data, int *psp_ret)
>>   {
>>          struct psp_device *psp = psp_master;
>>          struct sev_device *sev;
>>          unsigned int phys_lsb, phys_msb;
>>          unsigned int reg, ret = 0;
>> +       void *cmd_buf;
>>          int buf_len;
>>
>>          if (!psp || !psp->sev_data)
>> @@ -512,12 +819,28 @@ static int __sev_do_cmd_locked(int cmd, void *data, int *psp_ret)
>>           * work for some memory, e.g. vmalloc'd addresses, and @data may not be
>>           * physically contiguous.
>>           */
>> -       if (data)
>> -               memcpy(sev->cmd_buf, data, buf_len);
>> +       if (data) {
>> +               if (sev->cmd_buf_active > 2)
>> +                       return -EBUSY;
>> +
>> +               cmd_buf = sev->cmd_buf_active ? sev->cmd_buf_backup : sev->cmd_buf;
>> +
>> +               memcpy(cmd_buf, data, buf_len);
>> +               sev->cmd_buf_active++;
>> +
>> +               /*
>> +                * The behavior of the SEV-legacy commands is altered when the
>> +                * SNP firmware is in the INIT state.
>> +                */
>> +               if (need_firmware_copy(cmd) && snp_aware_copy_to_firmware(cmd, sev->cmd_buf))
>> +                       return -EFAULT;
>> +       } else {
>> +               cmd_buf = sev->cmd_buf;
>> +       }
>>
>>          /* Get the physical address of the command buffer */
>> -       phys_lsb = data ? lower_32_bits(__psp_pa(sev->cmd_buf)) : 0;
>> -       phys_msb = data ? upper_32_bits(__psp_pa(sev->cmd_buf)) : 0;
>> +       phys_lsb = data ? lower_32_bits(__psp_pa(cmd_buf)) : 0;
>> +       phys_msb = data ? upper_32_bits(__psp_pa(cmd_buf)) : 0;
>>
>>          dev_dbg(sev->dev, "sev command id %#x buffer 0x%08x%08x timeout %us\n",
>>                  cmd, phys_msb, phys_lsb, psp_timeout);
>> @@ -560,15 +883,24 @@ static int __sev_do_cmd_locked(int cmd, void *data, int *psp_ret)
>>                  ret = sev_write_init_ex_file_if_required(cmd);
>>          }
>>
>> -       print_hex_dump_debug("(out): ", DUMP_PREFIX_OFFSET, 16, 2, data,
>> -                            buf_len, false);
>> -
>>          /*
>>           * Copy potential output from the PSP back to data.  Do this even on
>>           * failure in case the caller wants to glean something from the error.
>>           */
>> -       if (data)
>> -               memcpy(data, sev->cmd_buf, buf_len);
>> +       if (data) {
>> +               /*
>> +                * Restore the page state after the command completes.
>> +                */
>> +               if (need_firmware_copy(cmd) &&
>> +                   snp_aware_copy_from_firmware(cmd, cmd_buf, ret))
>> +                       return -EFAULT;
>> +
>> +               memcpy(data, cmd_buf, buf_len);
>> +               sev->cmd_buf_active--;
>> +       }
>> +
>> +       print_hex_dump_debug("(out): ", DUMP_PREFIX_OFFSET, 16, 2, data,
>> +                            buf_len, false);
>>
>>          return ret;
>>   }
>> @@ -1579,10 +1911,12 @@ int sev_dev_init(struct psp_device *psp)
>>          if (!sev)
>>                  goto e_err;
>>
>> -       sev->cmd_buf = (void *)devm_get_free_pages(dev, GFP_KERNEL, 0);
>> +       sev->cmd_buf = (void *)devm_get_free_pages(dev, GFP_KERNEL, 1);
>>          if (!sev->cmd_buf)
>>                  goto e_sev;
>>
>> +       sev->cmd_buf_backup = (uint8_t *)sev->cmd_buf + PAGE_SIZE;
>> +
>>          psp->sev_data = sev;
>>
>>          sev->dev = dev;
>> @@ -1648,6 +1982,12 @@ static void sev_firmware_shutdown(struct sev_device *sev)
>>                  snp_range_list = NULL;
>>          }
>>
>> +       /*
>> +        * The host map need to clear the immutable bit so it must be free'd before the
>> +        * SNP firmware shutdown.
>> +        */
>> +       free_snp_host_map(sev);
>> +
>>          sev_snp_shutdown(&error);
>>   }
>>
>> @@ -1722,6 +2062,14 @@ void sev_pci_init(void)
>>                                  dev_err(sev->dev, "SEV-SNP: failed to INIT error %#x\n", error);
>>                          }
>>                  }
>> +
>> +               /*
>> +                * Allocate the intermediate buffers used for the legacy command handling.
>> +                */
>> +               if (alloc_snp_host_map(sev)) {
>> +                       dev_notice(sev->dev, "Failed to alloc host map (disabling legacy SEV)\n");
>> +                       goto skip_legacy;
>> +               }
>>          }
>>
>>          /* Obtain the TMR memory area for SEV-ES use */
>> @@ -1739,12 +2087,14 @@ void sev_pci_init(void)
>>                  dev_err(sev->dev, "SEV: failed to INIT error %#x, rc %d\n",
>>                          error, rc);
>>
>> +skip_legacy:
>>          dev_info(sev->dev, "SEV%s API:%d.%d build:%d\n", sev->snp_initialized ?
>>                  "-SNP" : "", sev->api_major, sev->api_minor, sev->build);
>>
>>          return;
>>
>>   err:
>> +       free_snp_host_map(sev);
>>          psp_master->sev_data = NULL;
>>   }
>>
>> diff --git a/drivers/crypto/ccp/sev-dev.h b/drivers/crypto/ccp/sev-dev.h
>> index 34767657beb5..19d79f9d4212 100644
>> --- a/drivers/crypto/ccp/sev-dev.h
>> +++ b/drivers/crypto/ccp/sev-dev.h
>> @@ -29,11 +29,20 @@
>>   #define SEV_CMDRESP_CMD_SHIFT          16
>>   #define SEV_CMDRESP_IOC                        BIT(0)
>>
>> +#define MAX_SNP_HOST_MAP_BUFS          2
>> +
>>   struct sev_misc_dev {
>>          struct kref refcount;
>>          struct miscdevice misc;
>>   };
>>
>> +struct snp_host_map {
>> +       u64 paddr;
>> +       u32 len;
>> +       void *host;
>> +       bool active;
>> +};
>> +
>>   struct sev_device {
>>          struct device *dev;
>>          struct psp_device *psp;
>> @@ -52,8 +61,11 @@ struct sev_device {
>>          u8 build;
>>
>>          void *cmd_buf;
>> +       void *cmd_buf_backup;
>> +       int cmd_buf_active;
>>
>>          bool snp_initialized;
>> +       struct snp_host_map snp_host_map[MAX_SNP_HOST_MAP_BUFS];
>>   };
>>
>>   int sev_dev_init(struct psp_device *psp);
>> --
>> 2.25.1
>>