From: Ahmad Fatoum <a.fatoum@xxxxxxxxxxxxxx>
libsystemd provides a sd_id128_get_machine_app_specific() function that
allows deriving an application specific UUID without directly leaking
the machine ID.
Let's provide an equivalent for barebox that will be used in a following
commit to generate a stable MAC instead of randomizing it.
Signed-off-by: Ahmad Fatoum <a.fatoum@xxxxxxxxxxxxxx>
---
common/machine_id.c | 83 +++++++++++++++++++++++++++++++++++++++++++-
include/linux/uuid.h | 8 +++++
include/machine_id.h | 11 ++++++
3 files changed, 101 insertions(+), 1 deletion(-)
diff --git a/common/machine_id.c b/common/machine_id.c
index f0b148fb9b99..e670886d8538 100644
--- a/common/machine_id.c
+++ b/common/machine_id.c
@@ -13,6 +13,7 @@
#define MACHINE_ID_LENGTH 32
+static bool __machine_id_initialized;
static void *__machine_id_hashable;
static size_t __machine_id_hashable_length;
@@ -22,13 +23,92 @@ const void *machine_id_get_hashable(size_t *len)
return __machine_id_hashable;
}
+/**
+ * machine_id_set_hashable - Provide per-board unique data
+ * @hashable: Buffer
+ * @len: size of buffer
+ *
+ * The data supplied to the last call of this function prior to
+ * late_initcall will be hashed and stored into global.machine_id,
+ * which can be later used for fixup into the kernel command line
+ * or for deriving application specific unique IDs via
+ * machine_id_get_app_specific().
+ */
void machine_id_set_hashable(const void *hashable, size_t len)
{
-
__machine_id_hashable = xmemdup(hashable, len);
__machine_id_hashable_length = len;
}
+/**
+ * machine_id_get_app_specific - Generates an application-specific UUID
+ * @result: UUID output of the function
+ * @...: pairs of (const void *, size_t) arguments of data to factor
+ * into the UUID followed by a NULL sentinel value.
+ *
+ * Combines the machine ID with the application specific varargs data
+ * to arrive at an application-specific and board-specific UUID that is
+ * stable and unique.
+ *
+ * The function returns 0 if a UUID was successfully written into @result
+ * and a negative error code otherwise.
+ */
+int machine_id_get_app_specific(uuid_t *result, ...)
+{
+ static u8 hmac[SHA256_DIGEST_SIZE];
+ const void *data;
+ size_t size;
+ va_list args;
+ struct digest *d;
+ int ret;
+
+ if (!__machine_id_initialized)
+ return -ENODATA;
+
+ d = digest_alloc("hmac(sha256)");
+ if (!d)
+ return -ENOSYS;
+
+ ret = digest_set_key(d, __machine_id_hashable, __machine_id_hashable_length);
+ if (ret)
+ goto out;
+
+ ret = digest_init(d);
+ if (ret)
+ goto out;
+
+ ret = -ENODATA;
+
+ va_start(args, result);
+
+ while ((data = va_arg(args, const void *))) {
+ size = va_arg(args, size_t);
+
+ ret = digest_update(d, data, size);
+ if (ret)
+ break;
+ }
+
+ va_end(args);
+
+ if (ret)
+ goto out;
+
+ ret = digest_final(d, hmac);
+ if (ret)
+ goto out;
+
+ /* Take only the first half. */
+ memcpy(result, hmac, min(sizeof(hmac), sizeof(*result)));
+
+ uuid_make_v4(result);
+
+out:
+ digest_free(d);
+
+ return ret;
+}
+
static int machine_id_set_globalvar(void)
{
struct digest *digest = NULL;
@@ -66,6 +146,7 @@ static int machine_id_set_globalvar(void)
env_machine_id = basprintf("%.*s", MACHINE_ID_LENGTH, hex_machine_id);
globalvar_add_simple("machine_id", env_machine_id);
free(env_machine_id);
+ __machine_id_initialized = true;
out:
digest_free(digest);
diff --git a/include/linux/uuid.h b/include/linux/uuid.h
index 6b1a3efa1e0b..1e4ffb343452 100644
--- a/include/linux/uuid.h
+++ b/include/linux/uuid.h
@@ -107,6 +107,14 @@ extern const u8 uuid_index[16];
int guid_parse(const char *uuid, guid_t *u);
int uuid_parse(const char *uuid, uuid_t *u);
+static inline void uuid_make_v4(uuid_t *u) {
+ /* Set UUID version to 4 --- truly random generation */
+ u->b[6] = (u->b[6] & 0x0F) | 0x40;
+
+ /* Set the UUID variant to DCE */
+ u->b[8] = (u->b[8] & 0x3F) | 0x80;
+}
+
/* MEI UUID type, don't use anywhere else */
#include <uapi/linux/uuid.h>
diff --git a/include/machine_id.h b/include/machine_id.h
index 9699e7f2072b..29600483ddc5 100644
--- a/include/machine_id.h
+++ b/include/machine_id.h
@@ -3,11 +3,15 @@
#ifndef __MACHINE_ID_H__
#define __MACHINE_ID_H__
+#include <linux/types.h>
+#include <linux/uuid.h>
+
#if IS_ENABLED(CONFIG_MACHINE_ID)
const void *machine_id_get_hashable(size_t *len);
void machine_id_set_hashable(const void *hashable, size_t len);
+int machine_id_get_app_specific(uuid_t *result, ...) __attribute__((__sentinel__));
#else
@@ -20,6 +24,13 @@ static inline void machine_id_set_hashable(const void *hashable, size_t len)
{
}
+static inline int machine_id_get_app_specific(uuid_t *result, ...)
+ __attribute__((__sentinel__));
+static inline int machine_id_get_app_specific(uuid_t *result, ...)
+{
+ return -ENOSYS;
+}
+
#endif /* CONFIG_MACHINE_ID */
#endif /* __MACHINE_ID_H__ */
--
2.42.0
