[PATCH v3 2/3] cryptodisk: add OS provided secret support

[James Bottomley <jejb@linux.ibm.com>]

Make use of the new OS provided secrets API so that if the new '-s'
option is passed in we try to extract the secret from the API rather
than prompting for it.

The primary consumer of this is AMD SEV, which has been programmed to
provide an injectable secret to the encrypted virtual machine.  OVMF
provides the secret area and passes it into the EFI Configuration
Tables.  The grub EFI layer pulls the secret out and primes the
secrets API with it.  The upshot of all of this is that a SEV
protected VM can do an encrypted boot with a protected boot secret.

Signed-off-by: James Bottomley <jejb@linux.ibm.com>

---

v2: add callback for after secret use
v3: update to use named module mechanism for secret loading
---
 grub-core/disk/cryptodisk.c | 77 +++++++++++++++++++++++++++++++++++--
 include/grub/cryptodisk.h   | 14 +++++++
 2 files changed, 87 insertions(+), 4 deletions(-)

diff --git a/grub-core/disk/cryptodisk.c b/grub-core/disk/cryptodisk.c
index c51c2edb8..c5eb45de4 100644
--- a/grub-core/disk/cryptodisk.c
+++ b/grub-core/disk/cryptodisk.c
@@ -41,6 +41,7 @@ static const struct grub_arg_option options[] =
     /* TRANSLATORS: It's still restricted to cryptodisks only.  */
     {"all", 'a', 0, N_("Mount all."), 0, 0},
     {"boot", 'b', 0, N_("Mount all volumes with `boot' flag set."), 0, 0},
+    {"secret", 's', 0, N_("Get secret passphrase from named module and optional identifier"), 0, 0},
     {0, 0, 0, 0, 0, 0}
   };
 
@@ -981,6 +982,10 @@ grub_util_cryptodisk_get_uuid (grub_disk_t disk)
 
 static int check_boot, have_it;
 static char *search_uuid;
+static char *os_passwd;
+
+/* variable to hold the list of secret providers */
+static struct grub_secret_entry *secret_providers;
 
 static void
 cryptodisk_close (grub_cryptodisk_t dev)
@@ -991,6 +996,21 @@ cryptodisk_close (grub_cryptodisk_t dev)
   grub_free (dev);
 }
 
+static int
+os_password_get(char buf[], unsigned len)
+{
+  if (!buf)
+    /* we're not interactive so no prompt */
+    return 0;
+
+  /* os_passwd should be null terminated, so just copy everything */
+  grub_strncpy(buf, os_passwd, len);
+  /* and add a terminator just in case */
+  buf[len - 1] = 0;
+
+  return 1;
+}
+
 static grub_err_t
 grub_cryptodisk_scan_device_real (const char *name, grub_disk_t source)
 {
@@ -1010,8 +1030,17 @@ grub_cryptodisk_scan_device_real (const char *name, grub_disk_t source)
       return grub_errno;
     if (!dev)
       continue;
-    
-    err = cr->recover_key (source, dev, grub_password_get);
+
+    if (os_passwd)
+      {
+	err = cr->recover_key (source, dev, os_password_get);
+	if (err)
+	  /* if the key doesn't work ignore the access denied error */
+	  grub_error_pop();
+      }
+    else
+      err = cr->recover_key (source, dev, grub_password_get);
+
     if (err)
     {
       cryptodisk_close (dev);
@@ -1027,6 +1056,18 @@ grub_cryptodisk_scan_device_real (const char *name, grub_disk_t source)
   return GRUB_ERR_NONE;
 }
 
+void
+grub_cryptodisk_add_secret_provider (struct grub_secret_entry *e)
+{
+  grub_list_push(GRUB_AS_LIST_P (&secret_providers), GRUB_AS_LIST (e));
+}
+
+void
+grub_cryptodisk_remove_secret_provider  (struct grub_secret_entry *e)
+{
+  grub_list_remove (GRUB_AS_LIST (e));
+}
+
 #ifdef GRUB_UTIL
 #include <grub/util/misc.h>
 grub_err_t
@@ -1103,7 +1144,7 @@ grub_cmd_cryptomount (grub_extcmd_context_t ctxt, int argc, char **args)
 {
   struct grub_arg_list *state = ctxt->state;
 
-  if (argc < 1 && !state[1].set && !state[2].set)
+  if (argc < 1 && !state[1].set && !state[2].set && !state[3].set)
     return grub_error (GRUB_ERR_BAD_ARGUMENT, "device name required");
 
   have_it = 0;
@@ -1121,6 +1162,7 @@ grub_cmd_cryptomount (grub_extcmd_context_t ctxt, int argc, char **args)
 
       check_boot = state[2].set;
       search_uuid = args[0];
+      os_passwd = NULL;
       grub_device_iterate (&grub_cryptodisk_scan_device, NULL);
       search_uuid = NULL;
 
@@ -1131,11 +1173,37 @@ grub_cmd_cryptomount (grub_extcmd_context_t ctxt, int argc, char **args)
   else if (state[1].set || (argc == 0 && state[2].set))
     {
       search_uuid = NULL;
+      os_passwd = NULL;
       check_boot = state[2].set;
       grub_device_iterate (&grub_cryptodisk_scan_device, NULL);
       search_uuid = NULL;
       return GRUB_ERR_NONE;
     }
+  else if (state[3].set)
+    {
+      struct grub_secret_entry *se;
+      grub_err_t rc;
+
+      if (argc < 1)
+	return grub_error (GRUB_ERR_BAD_ARGUMENT, "secret module must be specified");
+#ifndef GRUB_UTIL
+      grub_dl_load (args[0]);
+#endif
+      se = grub_named_list_find (GRUB_AS_NAMED_LIST (secret_providers), args[0]);
+      if (se == NULL)
+	return grub_error (GRUB_ERR_INVALID_COMMAND, "No secret provider is found");
+
+      rc = se->get (args[1], &os_passwd);
+      if (rc)
+	return rc;
+
+      search_uuid = NULL;
+      grub_device_iterate (&grub_cryptodisk_scan_device, NULL);
+      rc = se->put (args[1], have_it, &os_passwd);
+      os_passwd = NULL;
+
+      return rc;
+    }
   else
     {
       grub_err_t err;
@@ -1146,6 +1214,7 @@ grub_cmd_cryptomount (grub_extcmd_context_t ctxt, int argc, char **args)
       grub_size_t len;
 
       search_uuid = NULL;
+      os_passwd = NULL;
       check_boot = state[2].set;
       diskname = args[0];
       len = grub_strlen (diskname);
@@ -1313,7 +1382,7 @@ GRUB_MOD_INIT (cryptodisk)
 {
   grub_disk_dev_register (&grub_cryptodisk_dev);
   cmd = grub_register_extcmd ("cryptomount", grub_cmd_cryptomount, 0,
-			      N_("SOURCE|-u UUID|-a|-b"),
+			      N_("SOURCE|-u UUID|-a|-b|-s MOD [ID]"),
 			      N_("Mount a crypto device."), options);
   grub_procfs_register ("luks_script", &luks_script);
 }
diff --git a/include/grub/cryptodisk.h b/include/grub/cryptodisk.h
index 737487bb4..8ae5aed97 100644
--- a/include/grub/cryptodisk.h
+++ b/include/grub/cryptodisk.h
@@ -174,4 +174,18 @@ grub_util_get_geli_uuid (const char *dev);
 grub_cryptodisk_t grub_cryptodisk_get_by_uuid (const char *uuid);
 grub_cryptodisk_t grub_cryptodisk_get_by_source_disk (grub_disk_t disk);
 
+struct grub_secret_entry {
+  /* as named list */
+  struct grub_secret_entry *next;
+  struct grub_secret_entry **prev;
+  const char *name;
+
+  /* additional entries */
+  grub_err_t (*get)(const char *arg, char **secret);
+  grub_err_t (*put)(const char *arg, int have_it, char **secret);
+};
+
+void grub_cryptodisk_add_secret_provider (struct grub_secret_entry *e);
+void grub_cryptodisk_remove_secret_provider (struct grub_secret_entry *e);
+
 #endif
-- 
2.26.2