[U-Boot] [PATCH 12/14] fdt: Allow device tree to specify secure booting
Simon Glass
sjg at chromium.org
Fri Oct 26 04:31:09 CEST 2012
From: Doug Anderson <dianders at chromium.org>
When secure booting is chosen:
* The u-boot shell is never invoked during boot--we just do a simple
table lookup to find the command. This means we could even remove
the shell parsing from u-boot and still be able to boot.
* The boot command can't be interruped.
* Failure doesn't cause us to fall back to the shell.
Signed-off-by: Gabe Black <gabeblack at google.com>
Signed-off-by: Doug Anderson <dianders at chromium.org>
Signed-off-by: Simon Glass <sjg at chromium.org>
---
common/main.c | 62 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 files changed, 62 insertions(+), 0 deletions(-)
diff --git a/common/main.c b/common/main.c
index cf1b5f9..03c63b4 100644
--- a/common/main.c
+++ b/common/main.c
@@ -283,6 +283,59 @@ int abortboot(int bootdelay)
# endif /* CONFIG_AUTOBOOT_KEYED */
#endif /* CONFIG_BOOTDELAY >= 0 */
+/*
+ * Runs the given boot command securely. Specifically:
+ * - Doesn't run the command with the shell (run_command or parse_string_outer),
+ * since that's a lot of code surface that an attacker might exploit.
+ * Because of this, we don't do any argument parsing--the secure boot command
+ * has to be a full-fledged u-boot command.
+ * - Doesn't check for keypresses before booting, since that could be a
+ * security hole; also disables Ctrl-C.
+ * - Doesn't allow the command to return.
+ *
+ * Upon any failures, this function will drop into an infinite loop after
+ * printing the error message to console.
+ */
+
+#if defined(CONFIG_BOOTDELAY) && (CONFIG_BOOTDELAY >= 0) && \
+ defined(CONFIG_OF_CONTROL)
+static void secure_boot_cmd(char *cmd)
+{
+ cmd_tbl_t *cmdtp;
+ int rc;
+
+ if (!cmd) {
+ printf("## Error: Secure boot command not specified\n");
+ goto err;
+ }
+
+ /* Disable Ctrl-C just in case some command is used that checks it. */
+ disable_ctrlc(1);
+
+ /* Find the command directly. */
+ cmdtp = find_cmd(cmd);
+ if (!cmdtp) {
+ printf("## Error: \"%s\" not defined\n", cmd);
+ goto err;
+ }
+
+ /* Run the command, forcing no flags and faking argc and argv. */
+ rc = (cmdtp->cmd)(cmdtp, 0, 1, &cmd);
+
+ /* Shouldn't ever return from boot command. */
+ printf("## Error: \"%s\" returned (code %d)\n", cmd, rc);
+
+err:
+ /*
+ * Not a whole lot to do here. Rebooting won't help much, since we'll
+ * just end up right back here. Just loop.
+ */
+ hang();
+}
+
+#endif /* CONFIG_OF_CONTROL */
+
+
/****************************************************************************/
void main_loop (void)
@@ -397,6 +450,15 @@ void main_loop (void)
env = fdtdec_get_config_string(gd->fdt_blob, "bootcmd");
if (env)
s = env;
+
+ /*
+ * If the bootsecure option was chosen, use secure_boot_cmd().
+ * Always use 'env' in this case, since bootsecure requres that the
+ * bootcmd was specified in the FDT too.
+ */
+ if (fdtdec_get_config_int(gd->fdt_blob, "bootsecure", 0))
+ secure_boot_cmd(env);
+
#endif /* CONFIG_OF_CONTROL */
debug ("### main_loop: bootcmd=\"%s\"\n", s ? s : "<UNDEFINED>");
--
1.7.7.3
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