storage: flash_map: Add SHA-256 integrity method

Add SHA-256 flash integrity method.  It reads flash data from a
device giving an offset creating a SHA-256 hash to be compared
with a reference.  On sucess match, zero is returned, otherwise
a negative errno value.

Signed-off-by: Gerson Fernando Budke <nandojve@gmail.com>

include/storage/flash_map.h

@@ -75,6 +75,34 @@ struct flash_sector {
 	size_t fs_size; /** flash sector size */
 };
 
+#if defined(CONFIG_FLASH_AREA_CHECK_INTEGRITY)
+/**
+ * @brief Structure for verify flash region integrity
+ *
+ * This is used to pass data to be used to check flash integrity using SHA-256
+ * algorithm.
+ */
+struct flash_area_check {
+	const uint8_t *match;		/** 256 bits match vector */
+	size_t clen;			/** Content len to be compared */
+	size_t off;			/** Start Offset */
+	uint8_t *rbuf;			/** Temporary read buffer  */
+	size_t rblen;			/** Size of read buffer */
+};
+
+/**
+ * Verify flash memory length bytes integrity from a flash area. The start
+ * point is indicated by an offset value.
+ *
+ * @param[in] fa	Flash area
+ * @param[in] fic	Flash area check integrity data
+ *
+ * @return  0 on success, negative errno code on fail
+ */
+int flash_area_check_int_sha256(const struct flash_area *fa,
+				const struct flash_area_check *fac);
+#endif
+
 /**
  * @brief Retrieve partitions flash area from the flash_map.
  *

subsys/storage/flash_map/Kconfig

@@ -28,4 +28,12 @@ config FLASH_MAP_CUSTOM
 	  User must provide such a description in place of default on
 	  if had enabled this option.
 
+config FLASH_AREA_CHECK_INTEGRITY
+	bool "Enable flash check functions"
+	select TINYCRYPT
+	select TINYCRYPT_SHA256
+	help
+	  If enabled, there will be available the backend to check flash
+	  integrity using SHA-256 verification algorithm.
+
 endif

subsys/storage/flash_map/flash_map.c

@@ -2,6 +2,7 @@
  * Copyright (c) 2017 Nordic Semiconductor ASA
  * Copyright (c) 2015 Runtime Inc
  * Copyright (c) 2017 Linaro Ltd
+ * Copyright (c) 2020 Gerson Fernando Budke <nandojve@gmail.com>
  *
  * SPDX-License-Identifier: Apache-2.0
  */
@@ -15,6 +16,12 @@
 #include <soc.h>
 #include <init.h>
 
+#if defined(CONFIG_FLASH_AREA_CHECK_INTEGRITY)
+#include <tinycrypt/constants.h>
+#include <tinycrypt/sha256.h>
+#include <string.h>
+#endif
+
 #if defined(CONFIG_FLASH_PAGE_LAYOUT)
 struct layout_data {
 	uint32_t area_idx;
@@ -262,3 +269,60 @@ const struct device *flash_area_get_device(const struct flash_area *fa)
 {
 	return device_get_binding(fa->fa_dev_name);
 }
+
+#if defined(CONFIG_FLASH_AREA_CHECK_INTEGRITY)
+int flash_area_check_int_sha256(const struct flash_area *fa,
+				const struct flash_area_check *fac)
+{
+	unsigned char hash[TC_SHA256_DIGEST_SIZE];
+	struct tc_sha256_state_struct sha;
+	struct device *dev;
+	int to_read;
+	int pos;
+	int rc;
+
+	if (!fa || !fac || !fac->match || !fac->rbuf ||
+	    fac->clen <= 0 || fac->off < 0 || fac->rblen <= 0) {
+		return -EINVAL;
+	}
+
+	if (!is_in_flash_area_bounds(fa, fac->off, fac->clen)) {
+		return -EINVAL;
+	}
+
+	if (tc_sha256_init(&sha) != TC_CRYPTO_SUCCESS) {
+		return -ESRCH;
+	}
+
+	dev = device_get_binding(fa->fa_dev_name);
+	to_read = fac->rblen;
+
+	for (pos = 0; pos < fac->clen; pos += to_read) {
+		if (pos + to_read > fac->clen) {
+			to_read = fac->clen - pos;
+		}
+
+		rc = flash_read(dev, (fa->fa_off + fac->off + pos),
+				fac->rbuf, to_read);
+		if (rc != 0) {
+			return rc;
+		}
+
+		if (tc_sha256_update(&sha,
+				     fac->rbuf,
+				     to_read) != TC_CRYPTO_SUCCESS) {
+			return -ESRCH;
+		}
+	}
+
+	if (tc_sha256_final(hash, &sha) != TC_CRYPTO_SUCCESS) {
+		return -ESRCH;
+	}
+
+	if (memcmp(hash, fac->match, TC_SHA256_DIGEST_SIZE)) {
+		return -EILSEQ;
+	}
+
+	return 0;
+}
+#endif /* CONFIG_FLASH_AREA_CHECK_INTEGRITY */

tests/subsys/storage/flash_map/prj.conf

@@ -2,3 +2,4 @@ CONFIG_ZTEST=y
 CONFIG_FLASH=y
 CONFIG_FLASH_PAGE_LAYOUT=y
 CONFIG_FLASH_MAP=y
+CONFIG_FLASH_AREA_CHECK_INTEGRITY=y

tests/subsys/storage/flash_map/prj_native_posix.conf

@@ -2,3 +2,4 @@ CONFIG_ZTEST=y
 CONFIG_FLASH=y
 CONFIG_FLASH_PAGE_LAYOUT=y
 CONFIG_FLASH_MAP=y
+CONFIG_FLASH_AREA_CHECK_INTEGRITY=y

tests/subsys/storage/flash_map/prj_native_posix_64.conf

@@ -2,3 +2,4 @@ CONFIG_ZTEST=y
 CONFIG_FLASH=y
 CONFIG_FLASH_PAGE_LAYOUT=y
 CONFIG_FLASH_MAP=y
+CONFIG_FLASH_AREA_CHECK_INTEGRITY=y

tests/subsys/storage/flash_map/src/main.c

@@ -1,6 +1,7 @@
 /*
  * Copyright (c) 2017 Nordic Semiconductor ASA
  * Copyright (c) 2015 Runtime Inc
+ * Copyright (c) 2020 Gerson Fernando Budke <nandojve@gmail.com>
  *
  * SPDX-License-Identifier: Apache-2.0
  */
@@ -98,9 +99,70 @@ void test_flash_area_get_sectors(void)
 
 }
 
+void test_flash_area_check_int_sha256(void)
+{
+	/* echo $'0123456789abcdef\nfedcba98765432' > tst.sha
+	 * hexdump tst.sha
+	 */
+	uint8_t tst_vec[] = { 0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37,
+			      0x38, 0x39, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66,
+			      0x0a, 0x66, 0x65, 0x64, 0x63, 0x62, 0x61, 0x39,
+			      0x38, 0x37, 0x36, 0x35, 0x34, 0x33, 0x32, 0x0a };
+	/* sha256sum tst.sha */
+	uint8_t tst_sha[] = { 0x28, 0xf1, 0x6e, 0xea, 0xc3, 0xea, 0x89, 0x8d,
+			      0x80, 0x9e, 0x98, 0xeb, 0x09, 0x49, 0x98, 0x08,
+			      0x40, 0x69, 0x43, 0xa6, 0xef, 0xe1, 0xa3, 0xf9,
+			      0x3d, 0xdf, 0x15, 0x9e, 0x06, 0xf8, 0xdd, 0xbd };
+
+	const struct flash_area *fa;
+	struct flash_area_check fac = { NULL, 0, -1, NULL, 0 };
+	uint8_t buffer[16];
+	int rc;
+
+	rc = flash_area_open(FLASH_AREA_ID(image_1), &fa);
+	zassert_true(rc == 0, "flash_area_open() fail, error %d\n", rc);
+	rc = flash_area_erase(fa, 0, fa->fa_size);
+	zassert_true(rc == 0, "Flash erase failure (%d), error %d\n", rc);
+	rc = flash_area_write(fa, 0, tst_vec, sizeof(tst_vec));
+	zassert_true(rc == 0, "Flash img write, error %d\n", rc);
+
+	rc = flash_area_check_int_sha256(NULL, NULL);
+	zassert_true(rc == -EINVAL, "Flash area check int 256 params 1, 2\n");
+	rc = flash_area_check_int_sha256(NULL, &fac);
+	zassert_true(rc == -EINVAL, "Flash area check int 256 params 2\n");
+	rc = flash_area_check_int_sha256(fa, NULL);
+	zassert_true(rc == -EINVAL, "Flash area check int 256 params 1\n");
+
+	rc = flash_area_check_int_sha256(fa, &fac);
+	zassert_true(rc == -EINVAL, "Flash area check int 256 fac match\n");
+	fac.match = tst_sha;
+	rc = flash_area_check_int_sha256(fa, &fac);
+	zassert_true(rc == -EINVAL, "Flash area check int 256 fac clen\n");
+	fac.clen = sizeof(tst_vec);
+	rc = flash_area_check_int_sha256(fa, &fac);
+	zassert_true(rc == -EINVAL, "Flash area check int 256 fac off\n");
+	fac.off = 0;
+	rc = flash_area_check_int_sha256(fa, &fac);
+	zassert_true(rc == -EINVAL, "Flash area check int 256 fac rbuf\n");
+	fac.rbuf = buffer;
+	rc = flash_area_check_int_sha256(fa, &fac);
+	zassert_true(rc == -EINVAL, "Flash area check int 256 fac rblen\n");
+	fac.rblen = sizeof(buffer);
+
+	rc = flash_area_check_int_sha256(fa, &fac);
+	zassert_true(rc == 0, "Flash area check int 256 OK, error %d\n", rc);
+	tst_sha[0] = 0x00;
+	rc = flash_area_check_int_sha256(fa, &fac);
+	zassert_false(rc == 0, "Flash area check int 256 wrong sha\n");
+
+	flash_area_close(fa);
+}
+
 void test_main(void)
 {
 	ztest_test_suite(test_flash_map,
-			 ztest_unit_test(test_flash_area_get_sectors));
+			 ztest_unit_test(test_flash_area_get_sectors),
+			 ztest_unit_test(test_flash_area_check_int_sha256)
+			);
 	ztest_run_test_suite(test_flash_map);
 }