[U-Boot] [PATCH v2 4/4] autoboot.c: Add feature to stop autobooting via SHA256 encrypted password
Stefan Roese
sr at denx.de
Fri May 8 09:52:13 CEST 2015
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 at denx.de>
Cc: Simon Glass <sjg at chromium.org>
Cc: Magnus Lilja <lilja.magnus at 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");
--
2.4.0
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