common: machine_id: introduce machine id generation

This patch adds functionality to pass device-specific information that
will be hashed to generate a persistent unique machine id. It is then
available as global.machine_id. It can be overwritten with
nv.machine_id if necessary. Passing the machine id to the kernel is
done in a separate patch.

Note: if multiple sources provide hashable device-specific information
(via machine_id_set_hashable()) the information provided by the last call
prior to the late initcall set_machine_id() is used to generate the
machine id from. Thus when updating barebox the machine id might change.

Signed-off-by: Bastian Krause <bst@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

1 files changed, 69 insertions, 0 deletions

diff --git a/common/machine_id.c b/common/machine_id.c
new file mode 100644
index 0000000000..e678bb7fe8
--- /dev/null
+++ b/common/machine_id.c
@@ -0,0 +1,69 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2019 Pengutronix, Bastian Krause <kernel@pengutronix.de>
+ */
+
+#include <common.h>
+#include <init.h>
+#include <digest.h>
+#include <globalvar.h>
+#include <magicvar.h>
+#include <crypto/sha.h>
+#include <machine_id.h>
+
+#define MACHINE_ID_LENGTH 32
+
+static void *__machine_id_hashable;
+static size_t __machine_id_hashable_length;
+
+
+void machine_id_set_hashable(const void *hashable, size_t len)
+{
+
+	__machine_id_hashable = xmemdup(hashable, len);
+	__machine_id_hashable_length = len;
+}
+
+static int machine_id_set_bootarg(void)
+{
+	struct digest *digest = NULL;
+	unsigned char machine_id[SHA1_DIGEST_SIZE];
+	char hex_machine_id[MACHINE_ID_LENGTH];
+	char *env_machine_id;
+	int ret = 0;
+
+	/* nothing to do if no hashable information provided */
+	if (!__machine_id_hashable)
+		goto out;
+
+	digest = digest_alloc_by_algo(HASH_ALGO_SHA1);
+	ret = digest_init(digest);
+	if (ret)
+		goto out;
+
+	ret = digest_update(digest, __machine_id_hashable,
+			    __machine_id_hashable_length);
+	if (ret)
+		goto out;
+
+	ret = digest_final(digest, machine_id);
+	if (ret)
+		goto out;
+
+	/* use the first 16 bytes of the sha1 hash as the machine id */
+	bin2hex(hex_machine_id, machine_id, MACHINE_ID_LENGTH/2);
+
+	env_machine_id = basprintf("%.*s", MACHINE_ID_LENGTH, hex_machine_id);
+	globalvar_add_simple("machine_id", env_machine_id);
+	free(env_machine_id);
+
+out:
+	globalvar_add_simple("machine_id", NULL);
+
+	digest_free(digest);
+	return ret;
+
+}
+late_initcall(machine_id_set_bootarg);
+
+BAREBOX_MAGICVAR_NAMED(global_machine_id, global.machine_id, "Persistent device-specific, hexadecimal, 32-character id");