[PATCH] tlv: Add tlv_bind_serial mapping

[Jonas Rebmann <jre@pengutronix.de>]

Particularly when using secure boot with signed TLVs, it may be required
to issue and sign TLVs for specific units. As typically all units of a
board are compiled to validate TLVs against the same key, a "binding"
mechanism is needed if interchange of TLVs across those units must be
prevented. This mapping binds against the SoC serial number (a.k.a. SoC
UID) of the unit, rendering a signed TLV with such a field invalid for
all but one unit.

When generating TLVs that use this mapping, the exact case-sensitive
string representation of the serial_number must be taken into account:
All existing soc drivers supply the serial_number as uppercase
hexadecimal representation without a prefix.

Add the special mapping tlv_bind_serial that aborts TLV parsing if the
supplied string does not match the SoC serial number.

Include this mapping in barebox_tlv_v1_mappings with tag 0x0024 to make
it available in testing and in other setups using the generic tlv
parsers. These parsers will store the serial_number in the
"bound-serial-number" field.

Signed-off-by: Jonas Rebmann <jre@pengutronix.de>
---
 common/tlv/barebox.c | 32 ++++++++++++++++++++++++++++++++
 include/tlv/tlv.h    |  1 +
 2 files changed, 33 insertions(+)

diff --git a/common/tlv/barebox.c b/common/tlv/barebox.c
index 24de3eeaaa..cba9c3e2da 100644
--- a/common/tlv/barebox.c
+++ b/common/tlv/barebox.c
@@ -3,6 +3,10 @@
 #include <common.h>
 #include <net.h>
 #include <tlv/tlv.h>
+#include <driver.h>
+#include <param.h>
+#include <string.h>
+
 
 int tlv_handle_serial(struct tlv_device *dev, struct tlv_mapping *map, u16 len, const u8 *val)
 {
@@ -16,6 +20,32 @@ int tlv_handle_serial(struct tlv_device *dev, struct tlv_mapping *map, u16 len,
 	return 0;
 }
 
+int tlv_bind_serial(struct tlv_device *dev, struct tlv_mapping *map, u16 len, const u8 *val)
+{
+	struct bus_type *bus;
+	struct device_d *socdev;
+	const char *soc_serial;
+	char *tlv_serial = basprintf("%.*s", len, val);
+
+	bus = get_bus_by_name("soc");
+	if (!bus) {
+		pr_err("No 'soc' bus found\n");
+		return -EACCES;
+	}
+
+	for_each_device(socdev) {
+		soc_serial = dev_get_param(socdev, "serial_number");
+		if (!soc_serial)
+			continue;
+
+		if (streq_ptr(tlv_serial, soc_serial))
+			return __tlv_format_str(dev, map, len, val) ? 0 : -ENOMEM;
+
+	}
+
+	return -EACCES;
+}
+
 int tlv_handle_eth_address(struct tlv_device *dev, struct tlv_mapping *map, u16 len, const u8 *val)
 {
 	int i;
@@ -169,6 +199,8 @@ struct tlv_mapping barebox_tlv_v1_mappings[] = {
 	{ 0x0011, tlv_handle_eth_address, "ethernet-address" },
 	/* A sequence of multiple Ethernet addresses */
 	{ 0x0012, tlv_handle_eth_address_seq, "ethernet-address" },
+	/* Reject TLVs if device serial number string does not match CPU serial */
+	{ 0x0024, tlv_bind_serial, "bound-serial-number"},
 	{ /* sentintel */ },
 };
 
diff --git a/include/tlv/tlv.h b/include/tlv/tlv.h
index 536f61646c..cadade27b4 100644
--- a/include/tlv/tlv.h
+++ b/include/tlv/tlv.h
@@ -37,6 +37,7 @@ extern int tlv_format_hex(struct tlv_device *dev, struct tlv_mapping *map, u16 l
 extern int tlv_format_mac(struct tlv_device *dev, struct tlv_mapping *map, u16 len, const u8 *val);
 extern int tlv_format_blob(struct tlv_device *dev, struct tlv_mapping *map, u16 len, const u8 *val);
 extern int tlv_handle_serial(struct tlv_device *dev, struct tlv_mapping *map, u16 len, const u8 *val);
+extern int tlv_bind_serial(struct tlv_device *dev, struct tlv_mapping *map, u16 len, const u8 *val);
 extern int tlv_handle_eth_address(struct tlv_device *dev, struct tlv_mapping *map, u16 len, const u8 *val);
 extern int tlv_handle_eth_address_seq(struct tlv_device *dev, struct tlv_mapping *map, u16 len, const u8 *val);
 

---
base-commit: f485ddfccf960959d25462073528d314b8bf1aea
change-id: 20251112-tlv_bind_serial-b8b24a6fd4a0

Best regards,
--  
Jonas Rebmann <jre@pengutronix.de>