This patch adds the feature to only stop the autobooting, and therefor boot into the U-Boot prompt, when the input string / password matches a values that is encypted via a SHA256 hash and saved in the environment.
This feature is enabled by defined these config options: CONFIG_AUTOBOOT_KEYED CONFIG_AUTOBOOT_STOP_STR_SHA256
Signed-off-by: Stefan Roese sr@denx.de Cc: Simon Glass sjg@chromium.org Cc: Magnus Lilja lilja.magnus@gmail.com --- v2: - AUTOBOOT_STOP_STR_SHA256 is a string and not bool - Add input key length check as suggested by Magnus - Add "constant-length" time compare function as suggested by Magnus
common/Kconfig | 20 +++++++-- common/autoboot.c | 132 +++++++++++++++++++++++++++++++++++++++++++++--------- 2 files changed, 128 insertions(+), 24 deletions(-)
diff --git a/common/Kconfig b/common/Kconfig index ff150f0..71c5c10 100644 --- a/common/Kconfig +++ b/common/Kconfig @@ -45,9 +45,14 @@ config AUTOBOOT_PROMPT the responsibility of the user to select only such arguments that are valid in the given context.
+config AUTOBOOT_ENCRYPTION + bool "Enable encryption in autoboot stopping" + depends on AUTOBOOT_KEYED + default n + config AUTOBOOT_DELAY_STR string "Delay autobooting via specific input key / string" - depends on AUTOBOOT_KEYED + depends on AUTOBOOT_KEYED && !AUTOBOOT_ENCRYPTION help This option delays the automatic boot feature by issuing a specific input key or string. If CONFIG_AUTOBOOT_DELAY_STR @@ -59,7 +64,7 @@ config AUTOBOOT_DELAY_STR
config AUTOBOOT_STOP_STR string "Stop autobooting via specific input key / string" - depends on AUTOBOOT_KEYED + depends on AUTOBOOT_KEYED && !AUTOBOOT_ENCRYPTION help This option enables stopping (aborting) of the automatic boot feature only by issuing a specific input key or @@ -71,7 +76,7 @@ config AUTOBOOT_STOP_STR
config AUTOBOOT_KEYED_CTRLC bool "Enable Ctrl-C autoboot interruption" - depends on AUTOBOOT_KEYED + depends on AUTOBOOT_KEYED && !AUTOBOOT_ENCRYPTION default n help This option allows for the boot sequence to be interrupted @@ -79,6 +84,15 @@ config AUTOBOOT_KEYED_CTRLC Setting this variable provides an escape sequence from the limited "password" strings.
+config AUTOBOOT_STOP_STR_SHA256 + string "Stop autobooting via SHA256 encrypted password" + depends on AUTOBOOT_KEYED && AUTOBOOT_ENCRYPTION + help + This option adds the feature to only stop the autobooting, + and therefore boot into the U-Boot prompt, when the input + string / password matches a values that is encypted via + a SHA256 hash and saved in the environment. + endmenu
comment "Commands" diff --git a/common/autoboot.c b/common/autoboot.c index f72eb18..dde3d04 100644 --- a/common/autoboot.c +++ b/common/autoboot.c @@ -12,6 +12,7 @@ #include <fdtdec.h> #include <menu.h> #include <post.h> +#include <u-boot/sha256.h>
DECLARE_GLOBAL_DATA_PTR;
@@ -26,15 +27,80 @@ DECLARE_GLOBAL_DATA_PTR; /* Stored value of bootdelay, used by autoboot_command() */ static int stored_bootdelay;
-/*************************************************************************** - * Watch for 'delay' seconds for autoboot stop or autoboot delay string. - * returns: 0 - no key string, allow autoboot 1 - got key string, abort +#if defined(CONFIG_AUTOBOOT_KEYED) +#if defined(CONFIG_AUTOBOOT_STOP_STR_SHA256) + +/* + * Use a "constant-length" time compare function for this + * hash compare: + * + * https://crackstation.net/hashing-security.htm */ -# if defined(CONFIG_AUTOBOOT_KEYED) -static int abortboot_keyed(int bootdelay) +static int slow_equals(u8 *a, u8 *b, int len) +{ + int diff = 0; + int i; + + for (i = 0; i < len; i++) + diff |= a[i] ^ b[i]; + + return diff == 0; +} + +static int passwd_abort(uint64_t etime) +{ + const char *sha_env_str = getenv("bootstopkeysha256"); + u8 sha_env[SHA256_SUM_LEN]; + u8 sha[SHA256_SUM_LEN]; + char presskey[MAX_DELAY_STOP_STR]; + u_int presskey_len = 0; + int i; + int abort = 0; + + if (sha_env_str == NULL) + sha_env_str = CONFIG_AUTOBOOT_STOP_STR_SHA256; + + /* + * Generate the binary value from the environment hash value + * so that we can compare this value with the computed hash + * from the user input + */ + for (i = 0; i < SHA256_SUM_LEN; i++) { + char chr[3]; + + strncpy(chr, &sha_env_str[i * 2], 2); + sha_env[i] = simple_strtoul(chr, NULL, 16); + } + + /* + * We don't know how long the stop-string is, so we need to + * generate the sha256 hash upon each input character and + * compare the value with the one saved in the environment + */ + do { + if (tstc()) { + /* Check for input string overflow */ + if (presskey_len >= MAX_DELAY_STOP_STR) + return 0; + + presskey[presskey_len++] = getc(); + + /* Calculate sha256 upon each new char */ + sha256_csum_wd((unsigned char *)presskey, presskey_len, + sha, CHUNKSZ_SHA256); + + /* And check if sha matches saved value in env */ + if (slow_equals(sha, sha_env, SHA256_SUM_LEN)) + abort = 1; + } + } while (!abort && get_ticks() <= etime); + + return abort; +} +#else +static int passwd_abort(uint64_t etime) { int abort = 0; - uint64_t etime = endtick(bootdelay); struct { char *str; u_int len; @@ -42,7 +108,9 @@ static int abortboot_keyed(int bootdelay) } delaykey[] = { { .str = getenv("bootdelaykey"), .retry = 1 }, + { .str = getenv("bootdelaykey2"), .retry = 1 }, { .str = getenv("bootstopkey"), .retry = 0 }, + { .str = getenv("bootstopkey2"), .retry = 0 }, };
char presskey[MAX_DELAY_STOP_STR]; @@ -50,26 +118,21 @@ static int abortboot_keyed(int bootdelay) u_int presskey_max = 0; u_int i;
-#ifndef CONFIG_ZERO_BOOTDELAY_CHECK - if (bootdelay == 0) - return 0; -#endif - -# ifdef CONFIG_AUTOBOOT_PROMPT - /* - * CONFIG_AUTOBOOT_PROMPT includes the %d for all boards. - * To print the bootdelay value upon bootup. - */ - printf(CONFIG_AUTOBOOT_PROMPT, bootdelay); -# endif - # ifdef CONFIG_AUTOBOOT_DELAY_STR if (delaykey[0].str == NULL) delaykey[0].str = CONFIG_AUTOBOOT_DELAY_STR; # endif -# ifdef CONFIG_AUTOBOOT_STOP_STR +# ifdef CONFIG_AUTOBOOT_DELAY_STR2 if (delaykey[1].str == NULL) - delaykey[1].str = CONFIG_AUTOBOOT_STOP_STR; + delaykey[1].str = CONFIG_AUTOBOOT_DELAY_STR2; +# endif +# ifdef CONFIG_AUTOBOOT_STOP_STR + if (delaykey[2].str == NULL) + delaykey[2].str = CONFIG_AUTOBOOT_STOP_STR; +# endif +# ifdef CONFIG_AUTOBOOT_STOP_STR2 + if (delaykey[3].str == NULL) + delaykey[3].str = CONFIG_AUTOBOOT_STOP_STR2; # endif
for (i = 0; i < sizeof(delaykey) / sizeof(delaykey[0]); i++) { @@ -119,6 +182,33 @@ static int abortboot_keyed(int bootdelay) } } while (!abort && get_ticks() <= etime);
+ return abort; +} +#endif + +/*************************************************************************** + * Watch for 'delay' seconds for autoboot stop or autoboot delay string. + * returns: 0 - no key string, allow autoboot 1 - got key string, abort + */ +static int abortboot_keyed(int bootdelay) +{ + int abort; + uint64_t etime = endtick(bootdelay); + +#ifndef CONFIG_ZERO_BOOTDELAY_CHECK + if (bootdelay == 0) + return 0; +#endif + +# ifdef CONFIG_AUTOBOOT_PROMPT + /* + * CONFIG_AUTOBOOT_PROMPT includes the %d for all boards. + * To print the bootdelay value upon bootup. + */ + printf(CONFIG_AUTOBOOT_PROMPT, bootdelay); +# endif + + abort = passwd_abort(etime); if (!abort) debug_bootkeys("key timeout\n");