From: Doug Anderson dianders@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@google.com Signed-off-by: Doug Anderson dianders@chromium.org Signed-off-by: Simon Glass sjg@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>");