Re: [PATCH RFC v7 29/64] crypto: ccp: Handle the legacy SEV command when SNP is enabled
From: Kalra, Ashish
Date: Fri Jan 13 2023 - 17:48:26 EST
On 1/13/2023 4:42 PM, Alper Gun wrote:
On Fri, Jan 13, 2023 at 2:04 PM Kalra, Ashish <ashish.kalra@xxxxxxx> wrote:
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@xxxxxxx> wrote:
From: Brijesh Singh <brijesh.singh@xxxxxxx>
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@xxxxxxx>
Signed-off-by: Ashish Kalra <ashish.kalra@xxxxxxx>
Signed-off-by: Michael Roth <michael.roth@xxxxxxx>
---
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()?
yes, if we return here, these guest pages will be left in firmware state.
+
+ /* No need to go further if firmware failed to execute command. */
+ if (fw_err)
+ return 0;
Same thing also here, we are possibly leaving guest pages in the firmware state.
Yes, i agree, both are inhererent bugs in the original patch and need to
be fixed.
Thanks,
Ashish
+ }
+
+ 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