[U-Boot] [PATCH v1 4/4] autoboot.c: Add feature to stop autobooting via SHA256 encrypted password

Stefan Roese sr at denx.de
Thu May 7 14:13:32 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>

---

 common/Kconfig    |  20 ++++++++--
 common/autoboot.c | 112 +++++++++++++++++++++++++++++++++++++++++++-----------
 2 files changed, 107 insertions(+), 25 deletions(-)

diff --git a/common/Kconfig b/common/Kconfig
index ff150f0..5d06558 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
+	bool "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..0fca6af 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 +27,58 @@ 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)
-static int abortboot_keyed(int bootdelay)
+#if defined(CONFIG_AUTOBOOT_KEYED)
+#if defined(CONFIG_AUTOBOOT_STOP_STR_SHA256)
+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()) {
+			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 (memcmp(sha, sha_env, SHA256_SUM_LEN) == 0)
+				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 +86,9 @@ 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 +96,21 @@ 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 +160,33 @@ 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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