efi: honour SYSTEMD_EFI_OPTIONS even if we wouldn't honour SystemdOptions EFI var due to SecureBoot

poettering · poettering · commit 484f4e5b2d62 · 2020-04-30T12:12:14.000+02:00
Fixes: systemd#14864
diff --git a/src/basic/efivars.c b/src/basic/efivars.c
@@ -313,6 +313,29 @@ int systemd_efi_options_variable(char **line) {
                 return 0;
         }
 
+        /* In SecureBoot mode this is probably not what you want. As your cmdline is cryptographically signed
+         * like when using Type #2 EFI Unified Kernel Images (https://systemd.io/BOOT_LOADER_SPECIFICATION/)
+         * The user's intention is then that the cmdline should not be modified. You want to make sure that
+         * the system starts up as exactly specified in the signed artifact.
+         *
+         * (NB: to make testing purposes we still check the $SYSTEMD_EFI_OPTIONS env var above, even when in
+         * SecureBoot mode.) */
+        if (is_efi_secure_boot()) {
+                _cleanup_free_ char *k;
+
+                k = efi_variable_path(EFI_VENDOR_SYSTEMD, "SystemdOptions");
+                if (!k)
+                        return -ENOMEM;
+
+                /* Let's be helpful with the returned error and check if the variable exists at all. If it
+                 * does, let's return a recognizable error (EPERM), and if not ENODATA. */
+
+                if (access(k, F_OK) < 0)
+                        return errno == -ENOENT ? -ENODATA : -errno;
+
+                return -EPERM;
+        }
+
         r = efi_get_variable_string(EFI_VENDOR_SYSTEMD, "SystemdOptions", line);
         if (r == -ENOENT)
                 return -ENODATA;
diff --git a/src/basic/proc-cmdline.c b/src/basic/proc-cmdline.c
@@ -39,18 +39,6 @@ int proc_cmdline(char **ret) {
                 return read_one_line_file("/proc/cmdline", ret);
 }
 
-/* In SecureBoot mode this is probably not what you want. As your cmdline is
- * cryptographically signed like when using Type #2 EFI Unified Kernel Images
- * (https://systemd.io/BOOT_LOADER_SPECIFICATION/) The user's intention is then
- * that the cmdline should not be modified.  You want to make sure that the
- * system starts up as exactly specified in the signed artifact. */
-static int systemd_options_variable(char **line) {
-        if (is_efi_secure_boot())
-                return -ENODATA;
-
-        return systemd_efi_options_variable(line);
-}
-
 static int proc_cmdline_extract_first(const char **p, char **ret_word, ProcCmdlineFlags flags) {
         const char *q = *p;
         int r;
@@ -131,7 +119,7 @@ int proc_cmdline_parse(proc_cmdline_parse_t parse_item, void *data, ProcCmdlineF
 
         /* We parse the EFI variable first, because later settings have higher priority. */
 
-        r = systemd_options_variable(&line);
+        r = systemd_efi_options_variable(&line);
         if (r < 0 && r != -ENODATA)
                 log_debug_errno(r, "Failed to get SystemdOptions EFI variable, ignoring: %m");
 
@@ -262,7 +250,7 @@ int proc_cmdline_get_key(const char *key, ProcCmdlineFlags flags, char **ret_val
                 return r;
 
         line = mfree(line);
-        r = systemd_options_variable(&line);
+        r = systemd_efi_options_variable(&line);
         if (r == -ENODATA)
                 return false; /* Not found */
         if (r < 0)
