10.5. Runtime Security Subsystem (RSS)

This document focuses on the relationship between the Runtime Security Subsystem (RSS) and the application processor (AP). According to the ARM reference design the RSS is an independent core next to the AP and the SCP on the same die. It provides fundamental security guarantees and runtime services for the rest of the system (e.g.: trusted boot, measured boot, platform attestation, key management, and key derivation).

At power up RSS boots first from its private ROM code. It validates and loads its own images and the initial images of SCP and AP. When AP and SCP are released from reset and their initial code is loaded then they continue their own boot process, which is the same as on non-RSS systems. Please refer to the RSS documentation [1] for more details about the RSS boot flow.

The last stage of the RSS firmware is a persistent, runtime component. Much like AP_BL31, this is a passive entity which has no periodical task to do and just waits for external requests from other subsystems. RSS and other subsystems can communicate with each other over message exchange. RSS waits in idle for the incoming request, handles them, and sends a response then goes back to idle.

10.5.1. RSS communication layer

The communication between RSS and other subsystems are primarily relying on the Message Handling Unit (MHU) module. The number of MHU interfaces between RSS and other cores is IMPDEF. Besides MHU other modules also could take part in the communication. RSS is capable of mapping the AP memory to its address space. Thereby either RSS core itself or a DMA engine if it is present, can move the data between memory belonging to RSS or AP. In this way, a bigger amount of data can be transferred in a short time.

The MHU comes in pairs. There is a sender and receiver side. They are connected to each other. An MHU interface consists of two pairs of MHUs, one sender and one receiver on both sides. Bidirectional communication is possible over an interface. One pair provides message sending from AP to RSS and the other pair from RSS to AP. The sender and receiver are connected via channels. There is an IMPDEF number of channels (e.g: 4-16) between a sender and a receiver module.

The RSS communication layer provides two ways for message exchange:

  • Embedded messaging: The full message, including header and payload, are exchanged over the MHU channels. A channel is capable of delivering a single word. The sender writes the data to the channel register on its side and the receiver can read the data from the channel on the other side. One dedicated channel is used for signalling. It does not deliver any payload it is just meant for signalling that the sender loaded the data to the channel registers so the receiver can read them. The receiver uses the same channel to signal that data was read. Signalling happens via IRQ. If the message is longer than the data fit to the channel registers then the message is sent over in multiple rounds. Both, sender and receiver allocate a local buffer for the messages. Data is copied from/to these buffers to/from the channel registers.

  • Pointer-access messaging: The message header and the payload are separated and they are conveyed in different ways. The header is sent over the channels, similar to the embedded messaging but the payload is copied over by RSS core (or by DMA) between the sender and the receiver. This could be useful in the case of long messages because transaction time is less compared to the embedded messaging mode. Small payloads are copied by the RSS core because setting up DMA would require more CPU cycles. The payload is either copied into an internal buffer or directly read-written by RSS. Actual behavior depends on RSS setup, whether the partition supports memory-mapped iovec. Therefore, the sender must handle both cases and prevent access to the memory, where payload data lives, while the RSS handles the request.

The RSS communication layer supports both ways of messaging in parallel. It is decided at runtime based on the message size which way to transfer the message.

+----------------------------------------------+       +-------------------+
|                                              |       |                   |
|                      AP                      |       |                   |
|                                              |  +--->|       SRAM        |
+----------------------------------------------|  |    |                   |
|              BL1 / BL2 / BL31                |  |    |                   |
+----------------------------------------------+  |    +-------------------+
         |                           ^            |        ^           ^
         |  send                 IRQ | receive    |direct  |           |
         V                           |            |access  |           |
+--------------------+    +--------------------+  |        |           |
|      MHU sender    |    |    MHU receiver    |  |        | Copy data |
+--------------------+    +--------------------+  |        |           |
   | |           | |          | |           | |   |        |           |
   | | channels  | |          | | channels  | |   |        |           |
   | | e.g: 4-16 | |          | | e.g: 4-16 | |   |        V           |
+--------------------+    +--------------------+  |    +-------+       |
|     MHU receiver   |    |     MHU sender     |  | +->|  DMA  |       |
+--------------------+    +--------------------+  | |  +-------+       |
         |                           ^            | |      ^           |
    IRQ  |  receive                  | send       | |      | Copy data |
         V                           |            | |      V           V
+----------------------------------------------+  | |  +-------------------+
|                                              |--+-+  |                   |
|                  RSS                         |       |      SRAM         |
|                                              |       |                   |
+----------------------------------------------+       +-------------------+

Note

The RSS communication layer is not prepared for concurrent execution. The current use case only requires message exchange during the boot phase. In the boot phase, only a single core is running and the rest of the cores are in reset.

10.5.1.1. Message structure

A description of the message format can be found in the RSS communication design [2] document.

10.5.1.2. Source files

  • RSS comms: drivers/arm/rss

  • MHU driver: drivers/arm/mhu

10.5.1.3. API for communication over MHU

The API is defined in these header files:

  • include/drivers/arm/rss_comms.h

  • include/drivers/arm/mhu.h

10.5.2. RSS provided runtime services

RSS provides the following runtime services:

  • Measured boot: Securely store the firmware measurements which were computed during the boot process and the associated metadata (image description, measurement algorithm, etc.). More info on measured boot service in RSS can be found in the measured_boot_integration_guide [3] .

  • Delegated attestation: Query the platform attestation token and derive a delegated attestation key. More info on the delegated attestation service in RSS can be found in the delegated_attestation_integration_guide [4] .

  • OTP assets management: Public keys used by AP during the trusted boot process can be requested from RSS. Furthermore, AP can request RSS to increase a non-volatile counter. Please refer to the RSS key management [5] document for more details.

10.5.2.1. Runtime service API

The RSS provided runtime services implement a PSA aligned API. The parameter encoding follows the PSA client protocol described in the Firmware Framework for M [6] document in chapter 4.4. The implementation is restricted to the static handle use case therefore only the psa_call API is implemented.

10.5.2.2. Software and API layers

+----------------+         +---------------------+
|   BL1 / BL2    |         |       BL31          |
+----------------+         +---------------------+
  |                         |
  | extend_measurement()    | get_delegated_key()
  |                         | get_platform_token()
  V                         V
+----------------+         +---------------------+
|  PSA protocol  |         |    PSA protocol     |
+----------------+         +---------------------+
     |                               |
     | psa_call()                    | psa_call()
     |                               |
     V                               V
+------------------------------------------------+
|         RSS communication protocol             |
+------------------------------------------------+
     |                     ^
     | mhu_send_data()     | mhu_receive_data()
     |                     |
     V                     |
+------------------------------------------------+
|                 MHU driver                     |
+------------------------------------------------+
           |                      ^
           | Register access      | IRQ
           V                      |
+------------------------------------------------+
|             MHU HW on AP side                  |
+------------------------------------------------+
                     ^
                     | Physical wires
                     |
                     V
+------------------------------------------------+
|             MHU HW on RSS side                 |
+------------------------------------------------+
         |                        ^
         | IRQ                    | Register access
         V                        |
+------------------------------------------------+
|                 MHU driver                     |
+------------------------------------------------+
         |                        |
         V                        V
+---------------+       +------------------------+
| Measured boot |       | Delegated attestation  |
| service       |       | service                |
+---------------+       +------------------------+

10.5.3. RSS based Measured Boot

Measured Boot is the process of cryptographically measuring (computing the hash value of a binary) the code and critical data used at boot time. The measurement must be stored in a tamper-resistant way, so the security state of the device can be attested later to an external party. RSS provides a runtime service which is meant to store measurements and associated metadata alongside.

Data is stored in internal SRAM which is only accessible by the secure runtime firmware of RSS. Data is stored in so-called measurement slots. A platform has IMPDEF number of measurement slots. The measurement storage follows extend semantics. This means that measurements are not stored directly (as it was taken) instead they contribute to the current value of the measurement slot. The extension implements this logic, where || stands for concatenation:

new_value_of_measurement_slot = Hash(old_value_of_measurement_slot || measurement)

Supported hash algorithms: sha-256, sha-512

10.5.3.1. Measured Boot API

Defined here:

  • include/lib/psa/measured_boot.h

psa_status_t
rss_measured_boot_extend_measurement(uint8_t        index,
                                     const uint8_t *signer_id,
                                     size_t         signer_id_size,
                                     const uint8_t *version,
                                     size_t         version_size,
                                     uint32_t       measurement_algo,
                                     const uint8_t *sw_type,
                                     size_t         sw_type_size,
                                     const uint8_t *measurement_value,
                                     size_t         measurement_value_size,
                                     bool           lock_measurement);

10.5.3.2. Measured Boot Metadata

The following metadata can be stored alongside the measurement:

  • Signer-id: Mandatory. The hash of the firmware image signing public key.

  • Measurement algorithm: Optional. The hash algorithm which was used to compute the measurement (e.g.: sha-256, etc.).

  • Version info: Optional. The firmware version info (e.g.: 2.7).

  • SW type: Optional. Short text description (e.g.: BL1, BL2, BL31, etc.)

Note

Version info is not implemented in TF-A yet.

The caller must specify in which measurement slot to extend a certain measurement and metadata. A measurement slot can be extended by multiple measurements. The default value is IMPDEF. All measurement slot is cleared at reset, there is no other way to clear them. In the reference implementation, the measurement slots are initialized to 0. At the first call to extend the measurement in a slot, the extend operation uses the default value of the measurement slot. All upcoming extend operation on the same slot contributes to the previous value of that measurement slot.

The following rules are kept when a slot is extended multiple times:

  • Signer-id must be the same as the previous call(s), otherwise a PSA_ERROR_NOT_PERMITTED error code is returned.

  • Measurement algorithm: must be the same as the previous call(s), otherwise, a PSA_ERROR_NOT_PERMITTED error code is returned.

In case of error no further action is taken (slot is not locked). If there is a valid data in a sub-sequent call then measurement slot will be extended. The rest of the metadata is handled as follows when a measurement slot is extended multiple times:

  • SW type: Cleared.

  • Version info: Cleared.

Note

Extending multiple measurements in the same slot leads to some metadata information loss. Since RSS is not constrained on special HW resources to store the measurements and metadata, therefore it is worth considering to store all of them one by one in distinct slots. However, they are one-by-one included in the platform attestation token. So, the number of distinct firmware image measurements has an impact on the size of the attestation token.

The allocation of the measurement slot among RSS, Root and Realm worlds is platform dependent. The platform must provide an allocation of the measurement slot at build time. An example can be found in tf-a/plat/arm/board/tc/tc_bl1_measured_boot.c Furthermore, the memory, which holds the metadata is also statically allocated in RSS memory. Some of the fields have a static value (measurement algorithm), and some of the values have a dynamic value (measurement value) which is updated by the bootloaders when the firmware image is loaded and measured. The metadata structure is defined in include/drivers/measured_boot/rss/rss_measured_boot.h.

struct rss_mboot_metadata {
        unsigned int id;
        uint8_t slot;
        uint8_t signer_id[SIGNER_ID_MAX_SIZE];
        size_t  signer_id_size;
        uint8_t version[VERSION_MAX_SIZE];
        size_t  version_size;
        uint8_t sw_type[SW_TYPE_MAX_SIZE];
        size_t  sw_type_size;
        void    *pk_oid;
        bool    lock_measurement;
};

10.5.3.3. Signer-ID API

This function calculates the hash of a public key (signer-ID) using the Measurement algorithm and stores it in the rss_mboot_metadata field named signer_id. Prior to calling this function, the caller must ensure that the signer_id field points to the zero-filled buffer.

Defined here:

  • include/drivers/measured_boot/rss/rss_measured_boot.h

int rss_mboot_set_signer_id(struct rss_mboot_metadata *metadata_ptr,
                            const void *pk_oid,
                            const void *pk_ptr,
                            size_t pk_len)
  • First parameter is the pointer to the rss_mboot_metadata structure.

  • Second parameter is the pointer to the key-OID of the public key.

  • Third parameter is the pointer to the public key buffer.

  • Fourth parameter is the size of public key buffer.

  • This function returns 0 on success, a signed integer error code otherwise.

10.5.3.4. Build time config options

  • MEASURED_BOOT: Enable measured boot. It depends on the platform implementation whether RSS or TPM (or both) backend based measured boot is enabled.

  • MBOOT_RSS_HASH_ALG: Determine the hash algorithm to measure the images. The default value is sha-256.

10.5.3.5. Measured boot flow

../_images/rss_measured_boot_flow.svg

10.5.3.6. Sample console log

INFO:    Measured boot extend measurement:
INFO:     - slot        : 6
INFO:     - signer_id   : 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
INFO:                   : 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
INFO:     - version     :
INFO:     - version_size: 0
INFO:     - sw_type     : FW_CONFIG
INFO:     - sw_type_size: 10
INFO:     - algorithm   : 2000009
INFO:     - measurement : aa ea d3 a7 a8 e2 ab 7d 13 a6 cb 34 99 10 b9 a1
INFO:                   : 1b 9f a0 52 c5 a8 b1 d7 76 f2 c1 c1 ef ca 1a df
INFO:     - locking     : true
INFO:    FCONF: Config file with image ID:31 loaded at address = 0x4001010
INFO:    Loading image id=24 at address 0x4001300
INFO:    Image id=24 loaded: 0x4001300 - 0x400153a
INFO:    Measured boot extend measurement:
INFO:     - slot        : 7
INFO:     - signer_id   : b0 f3 82 09 12 97 d8 3a 37 7a 72 47 1b ec 32 73
INFO:                   : e9 92 32 e2 49 59 f6 5e 8b 4a 4a 46 d8 22 9a da
INFO:     - version     :
INFO:     - version_size: 0
INFO:     - sw_type     : TB_FW_CONFIG
INFO:     - sw_type_size: 13
INFO:     - algorithm   : 2000009
INFO:     - measurement : 05 b9 dc 98 62 26 a7 1c 2d e5 bb af f0 90 52 28
INFO:                   : f2 24 15 8a 3a 56 60 95 d6 51 3a 7a 1a 50 9b b7
INFO:     - locking     : true
INFO:    FCONF: Config file with image ID:24 loaded at address = 0x4001300
INFO:    BL1: Loading BL2
INFO:    Loading image id=1 at address 0x404d000
INFO:    Image id=1 loaded: 0x404d000 - 0x406412a
INFO:    Measured boot extend measurement:
INFO:     - slot        : 8
INFO:     - signer_id   : b0 f3 82 09 12 97 d8 3a 37 7a 72 47 1b ec 32 73
INFO:                   : e9 92 32 e2 49 59 f6 5e 8b 4a 4a 46 d8 22 9a da
INFO:     - version     :
INFO:     - version_size: 0
INFO:     - sw_type     : BL_2
INFO:     - sw_type_size: 5
INFO:     - algorithm   : 2000009
INFO:     - measurement : 53 a1 51 75 25 90 fb a1 d9 b8 c8 34 32 3a 01 16
INFO:                   : c9 9e 74 91 7d 28 02 56 3f 5c 40 94 37 58 50 68
INFO:     - locking     : true

10.5.4. Delegated Attestation

Delegated Attestation Service was mainly developed to support the attestation flow on the ARM Confidential Compute Architecture (ARM CCA) [7]. The detailed description of the delegated attestation service can be found in the Delegated Attestation Service Integration Guide [4] document.

In the CCA use case, the Realm Management Monitor (RMM) relies on the delegated attestation service of the RSS to get a realm attestation key and the CCA platform token. BL31 does not use the service for its own purpose, only calls it on behalf of RMM. The access to MHU interface and thereby to RSS is restricted to BL31 only. Therefore, RMM does not have direct access, all calls need to go through BL31. The RMM dispatcher module of the BL31 is responsible for delivering the calls between the two parties.

Note

Currently the connection between the RMM dispatcher and the PSA/RSS layer is not yet implemented. RMM dispatcher just returns hard coded data.

10.5.4.1. Delegated Attestation API

Defined here:

  • include/lib/psa/delegated_attestation.h

psa_status_t
rss_delegated_attest_get_delegated_key(uint8_t   ecc_curve,
                                       uint32_t  key_bits,
                                       uint8_t  *key_buf,
                                       size_t    key_buf_size,
                                       size_t   *key_size,
                                       uint32_t  hash_algo);

psa_status_t
rss_delegated_attest_get_token(const uint8_t *dak_pub_hash,
                               size_t         dak_pub_hash_size,
                               uint8_t       *token_buf,
                               size_t         token_buf_size,
                               size_t        *token_size);

10.5.4.2. Attestation flow

../_images/rss_attestation_flow.svg

10.5.4.3. Sample attestation token

Binary format:

INFO:    DELEGATED ATTEST TEST START
INFO:    Get delegated attestation key start
INFO:    Get delegated attest key succeeds, len: 48
INFO:    Delegated attest key:
INFO:            0d 2a 66 61 d4 89 17 e1 70 c6 73 56 df f4 11 fd
INFO:            7d 1f 3b 8a a3 30 3d 70 4c d9 06 c3 c7 ef 29 43
INFO:            0f ee b5 e7 56 e0 71 74 1b c4 39 39 fd 85 f6 7b
INFO:    Get platform token start
INFO:    Get platform token succeeds, len: 1086
INFO:    Platform attestation token:
INFO:            d2 84 44 a1 01 38 22 a0 59 03 d1 a9 0a 58 20 00
INFO:            00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
INFO:            00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 19
INFO:            01 00 58 21 01 cb 8c 79 f7 a0 0a 6c ce 12 66 f8
INFO:            64 45 48 42 0e c5 10 bf 84 ee 22 18 b9 8f 11 04
INFO:            c7 22 31 9d fb 19 09 5c 58 20 aa aa aa aa aa aa
INFO:            aa aa bb bb bb bb bb bb bb bb cc cc cc cc cc cc
INFO:            cc cc dd dd dd dd dd dd dd dd 19 09 5b 19 30 00
INFO:            19 09 5f 89 a4 05 58 20 bf e6 d8 6f 88 26 f4 ff
INFO:            97 fb 96 c4 e6 fb c4 99 3e 46 19 fc 56 5d a2 6a
INFO:            df 34 c3 29 48 9a dc 38 04 67 31 2e 36 2e 30 2b
INFO:            30 01 64 52 54 5f 30 02 58 20 90 27 f2 46 ab 31
INFO:            85 36 46 c4 d7 c6 60 ed 31 0d 3c f0 14 de f0 6c
INFO:            24 0b de b6 7a 84 fc 3f 5b b7 a4 05 58 20 b3 60
INFO:            ca f5 c9 8c 6b 94 2a 48 82 fa 9d 48 23 ef b1 66
INFO:            a9 ef 6a 6e 4a a3 7c 19 19 ed 1f cc c0 49 04 67
INFO:            30 2e 30 2e 30 2b 30 01 64 52 54 5f 31 02 58 20
INFO:            52 13 15 d4 9d b2 cf 54 e4 99 37 44 40 68 f0 70
INFO:            7d 73 64 ae f7 08 14 b0 f7 82 ad c6 17 db a3 91
INFO:            a4 05 58 20 bf e6 d8 6f 88 26 f4 ff 97 fb 96 c4
INFO:            e6 fb c4 99 3e 46 19 fc 56 5d a2 6a df 34 c3 29
INFO:            48 9a dc 38 04 67 31 2e 35 2e 30 2b 30 01 64 52
INFO:            54 5f 32 02 58 20 8e 5d 64 7e 6f 6c c6 6f d4 4f
INFO:            54 b6 06 e5 47 9a cc 1b f3 7f ce 87 38 49 c5 92
INFO:            d8 2f 85 2e 85 42 a4 05 58 20 bf e6 d8 6f 88 26
INFO:            f4 ff 97 fb 96 c4 e6 fb c4 99 3e 46 19 fc 56 5d
INFO:            a2 6a df 34 c3 29 48 9a dc 38 04 67 31 2e 35 2e
INFO:            30 2b 30 01 60 02 58 20 b8 01 65 a7 78 8b c6 59
INFO:            42 8d 33 10 85 d1 49 0a dc 9e c3 ee df 85 1b d2
INFO:            f0 73 73 6a 0c 07 11 b8 a4 05 58 20 b0 f3 82 09
INFO:            12 97 d8 3a 37 7a 72 47 1b ec 32 73 e9 92 32 e2
INFO:            49 59 f6 5e 8b 4a 4a 46 d8 22 9a da 04 60 01 6a
INFO:            46 57 5f 43 4f 4e 46 49 47 00 02 58 20 21 9e a0
INFO:            13 82 e6 d7 97 5a 11 13 a3 5f 45 39 68 b1 d9 a3
INFO:            ea 6a ab 84 23 3b 8c 06 16 98 20 ba b9 a4 05 58
INFO:            20 b0 f3 82 09 12 97 d8 3a 37 7a 72 47 1b ec 32
INFO:            73 e9 92 32 e2 49 59 f6 5e 8b 4a 4a 46 d8 22 9a
INFO:            da 04 60 01 6d 54 42 5f 46 57 5f 43 4f 4e 46 49
INFO:            47 00 02 58 20 41 39 f6 c2 10 84 53 c5 17 ae 9a
INFO:            e5 be c1 20 7b cc 24 24 f3 9d 20 a8 fb c7 b3 10
INFO:            e3 ee af 1b 05 a4 05 58 20 b0 f3 82 09 12 97 d8
INFO:            3a 37 7a 72 47 1b ec 32 73 e9 92 32 e2 49 59 f6
INFO:            5e 8b 4a 4a 46 d8 22 9a da 04 60 01 65 42 4c 5f
INFO:            32 00 02 58 20 5c 96 20 e1 e3 3b 0f 2c eb c1 8e
INFO:            1a 02 a6 65 86 dd 34 97 a7 4c 98 13 bf 74 14 45
INFO:            2d 30 28 05 c3 a4 05 58 20 b0 f3 82 09 12 97 d8
INFO:            3a 37 7a 72 47 1b ec 32 73 e9 92 32 e2 49 59 f6
INFO:            5e 8b 4a 4a 46 d8 22 9a da 04 60 01 6e 53 45 43
INFO:            55 52 45 5f 52 54 5f 45 4c 33 00 02 58 20 f6 fb
INFO:            62 99 a5 0c df db 02 0b 72 5b 1c 0b 63 6e 94 ee
INFO:            66 50 56 3a 29 9c cb 38 f0 ec 59 99 d4 2e a4 05
INFO:            58 20 b0 f3 82 09 12 97 d8 3a 37 7a 72 47 1b ec
INFO:            32 73 e9 92 32 e2 49 59 f6 5e 8b 4a 4a 46 d8 22
INFO:            9a da 04 60 01 6a 48 57 5f 43 4f 4e 46 49 47 00
INFO:            02 58 20 98 5d 87 21 84 06 33 9d c3 1f 91 f5 68
INFO:            8d a0 5a f0 d7 7e 20 51 ce 3b f2 a5 c3 05 2e 3c
INFO:            8b 52 31 19 01 09 78 1c 68 74 74 70 3a 2f 2f 61
INFO:            72 6d 2e 63 6f 6d 2f 43 43 41 2d 53 53 44 2f 31
INFO:            2e 30 2e 30 19 09 62 71 6e 6f 74 2d 68 61 73 68
INFO:            2d 65 78 74 65 6e 64 65 64 19 09 61 44 ef be ad
INFO:            de 19 09 60 77 77 77 77 2e 74 72 75 73 74 65 64
INFO:            66 69 72 6d 77 61 72 65 2e 6f 72 67 58 60 29 4e
INFO:            4a d3 98 1e 3b 70 9f b6 66 ed 47 33 0e 99 f0 b1
INFO:            c3 f2 bc b2 1d b0 ae 90 0c c4 82 ff a2 6f ae 45
INFO:            f6 87 09 4a 09 21 77 ec 36 1c 53 b8 a7 9b 8e f7
INFO:            27 eb 7a 09 da 6f fb bf cb fd b3 e5 e9 36 91 b1
INFO:            92 13 c1 30 16 b4 5c 49 5e c0 c1 b9 01 5c 88 2c
INFO:            f8 2f 3e a4 a2 6d e4 9d 31 6a 06 f7 a7 73
INFO:    DELEGATED ATTEST TEST END

JSON format:

{
    "CCA_PLATFORM_CHALLENGE": "b'0000000000000000000000000000000000000000000000000000000000000000'",
    "CCA_PLATFORM_INSTANCE_ID": "b'01CB8C79F7A00A6CCE1266F8644548420EC510BF84EE2218B98F1104C722319DFB'",
    "CCA_PLATFORM_IMPLEMENTATION_ID": "b'AAAAAAAAAAAAAAAABBBBBBBBBBBBBBBBCCCCCCCCCCCCCCCCDDDDDDDDDDDDDDDD'",
    "CCA_PLATFORM_LIFECYCLE": "secured_3000",
    "CCA_PLATFORM_SW_COMPONENTS": [
        {
            "SIGNER_ID": "b'BFE6D86F8826F4FF97FB96C4E6FBC4993E4619FC565DA26ADF34C329489ADC38'",
            "SW_COMPONENT_VERSION": "1.6.0+0",
            "SW_COMPONENT_TYPE": "RT_0",
            "MEASUREMENT_VALUE": "b'9027F246AB31853646C4D7C660ED310D3CF014DEF06C240BDEB67A84FC3F5BB7'"
        },
        {
            "SIGNER_ID": "b'B360CAF5C98C6B942A4882FA9D4823EFB166A9EF6A6E4AA37C1919ED1FCCC049'",
            "SW_COMPONENT_VERSION": "0.0.0+0",
            "SW_COMPONENT_TYPE": "RT_1",
            "MEASUREMENT_VALUE": "b'521315D49DB2CF54E49937444068F0707D7364AEF70814B0F782ADC617DBA391'"
        },
        {
            "SIGNER_ID": "b'BFE6D86F8826F4FF97FB96C4E6FBC4993E4619FC565DA26ADF34C329489ADC38'",
            "SW_COMPONENT_VERSION": "1.5.0+0",
            "SW_COMPONENT_TYPE": "RT_2",
            "MEASUREMENT_VALUE": "b'8E5D647E6F6CC66FD44F54B606E5479ACC1BF37FCE873849C592D82F852E8542'"
        },
        {
            "SIGNER_ID": "b'BFE6D86F8826F4FF97FB96C4E6FBC4993E4619FC565DA26ADF34C329489ADC38'",
            "SW_COMPONENT_VERSION": "1.5.0+0",
            "SW_COMPONENT_TYPE": "",
            "MEASUREMENT_VALUE": "b'B80165A7788BC659428D331085D1490ADC9EC3EEDF851BD2F073736A0C0711B8'"
        },
        {
            "SIGNER_ID": "b'b0f382091297d83a377a72471bec3273e99232e24959f65e8b4a4a46d8229ada'",
            "SW_COMPONENT_VERSION": "",
            "SW_COMPONENT_TYPE": "FW_CONFIG\u0000",
            "MEASUREMENT_VALUE": "b'219EA01382E6D7975A1113A35F453968B1D9A3EA6AAB84233B8C06169820BAB9'"
        },
        {
            "SIGNER_ID": "b'b0f382091297d83a377a72471bec3273e99232e24959f65e8b4a4a46d8229ada'",
            "SW_COMPONENT_VERSION": "",
            "SW_COMPONENT_TYPE": "TB_FW_CONFIG\u0000",
            "MEASUREMENT_VALUE": "b'4139F6C2108453C517AE9AE5BEC1207BCC2424F39D20A8FBC7B310E3EEAF1B05'"
        },
        {
            "SIGNER_ID": "b'b0f382091297d83a377a72471bec3273e99232e24959f65e8b4a4a46d8229ada'",
            "SW_COMPONENT_VERSION": "",
            "SW_COMPONENT_TYPE": "BL_2\u0000",
            "MEASUREMENT_VALUE": "b'5C9620E1E33B0F2CEBC18E1A02A66586DD3497A74C9813BF7414452D302805C3'"
        },
        {
            "SIGNER_ID": "b'b0f382091297d83a377a72471bec3273e99232e24959f65e8b4a4a46d8229ada'",
            "SW_COMPONENT_VERSION": "",
            "SW_COMPONENT_TYPE": "SECURE_RT_EL3\u0000",
            "MEASUREMENT_VALUE": "b'F6FB6299A50CDFDB020B725B1C0B636E94EE6650563A299CCB38F0EC5999D42E'"
        },
        {
            "SIGNER_ID": "b'b0f382091297d83a377a72471bec3273e99232e24959f65e8b4a4a46d8229ada'",
            "SW_COMPONENT_VERSION": "",
            "SW_COMPONENT_TYPE": "HW_CONFIG\u0000",
            "MEASUREMENT_VALUE": "b'985D87218406339DC31F91F5688DA05AF0D77E2051CE3BF2A5C3052E3C8B5231'"
        }
    ],
    "CCA_ATTESTATION_PROFILE": "http://arm.com/CCA-SSD/1.0.0",
    "CCA_PLATFORM_HASH_ALGO_ID": "not-hash-extended",
    "CCA_PLATFORM_CONFIG": "b'EFBEADDE'",
    "CCA_PLATFORM_VERIFICATION_SERVICE": "www.trustedfirmware.org"
}

10.5.5. RSS OTP Assets Management

RSS provides access for AP to assets in OTP, which include keys for image signature verification and non-volatile counters for anti-rollback protection.

10.5.5.1. Non-Volatile Counter API

AP/RSS interface for retrieving and incrementing non-volatile counters API is as follows.

Defined here:

  • include/lib/psa/rss_platform_api.h

psa_status_t rss_platform_nv_counter_increment(uint32_t counter_id)

psa_status_t rss_platform_nv_counter_read(uint32_t counter_id,
        uint32_t size, uint8_t *val)

Through this service, we can read/increment any of the 3 non-volatile counters used on an Arm CCA platform:

  • Non-volatile counter for CCA firmware (BL2, BL31, RMM).

  • Non-volatile counter for secure firmware.

  • Non-volatile counter for non-secure firmware.

10.5.5.2. Public Key API

AP/RSS interface for reading the ROTPK is as follows.

Defined here:

  • include/lib/psa/rss_platform_api.h

psa_status_t rss_platform_key_read(enum rss_key_id_builtin_t key,
        uint8_t *data, size_t data_size, size_t *data_length)

Through this service, we can read any of the 3 ROTPKs used on an Arm CCA platform:

  • ROTPK for CCA firmware (BL2, BL31, RMM).

  • ROTPK for secure firmware.

  • ROTPK for non-secure firmware.

10.5.6. References


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