[PATCH 3/5] doc: imx: ahab: add AHAB introduction
Jérémie Dautheribes (Schneider Electric) via U-Bo ot <[email protected]>
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Add an introductory document describing the AHAB (Advanced High Assurance Boot) secure and encrypted boot flow, covering the following topics: - AHAB architecture overview (SCU, SECO, PKI tree) - AHAB secure boot and encrypted boot flow - PKI tree generation (ahab_pki_tree.sh) - SRK Table and SRK Hash generation (srktool) - SRK Hash fuse programming and sanity check notes - i.MX 8ULP/93 secure boot support This is based on doc/imx/ahab/introduction_ahab.txt from uboot-imx (lf_v2026.04). Originally written by Breno Lima, with contributions from Ye Li, Vanessa Maegima, and Utkarsh Gupta upstream in uboot-imx. Signed-off-by: Jérémie Dautheribes (Schneider Electric) <[email protected]> --- doc/imx/ahab/introduction_ahab.txt | 445 +++++++++++++++++++++++++++++++++++++ 1 file changed, 445 insertions(+) diff --git a/doc/imx/ahab/introduction_ahab.txt b/doc/imx/ahab/introduction_ahab.txt new file mode 100644 index 00000000000..4a5b6f795c4 --- /dev/null +++ b/doc/imx/ahab/introduction_ahab.txt @@ -0,0 +1,445 @@ + +=======================================================+ + + i.MX Secure and Encrypted Boot using AHAB + + +=======================================================+ + +1. Introduction +---------------- + +The i.MX 8/8x/8ULP/9x family of applications processors introduce a new secure +boot concept. Due to the multi-core architecture, the Security Controller (SECO) +and System Control Unit (SCU) in i.MX 8/8x, and Edgelock secure enclave (ELE) +in i.MX 8ULP/9x are heavily involved in the secure boot process. + +Step-by-step guides are available under doc/imx/ahab/guides/ directory, +users familiar with AHAB architecture and CST PKI tree generation should +refer to these documents instead. + +1.1 The AHAB Secure Boot Architecture +-------------------------------------- + +The Advanced High Assurance Boot (AHAB) feature relies in digital signatures to +prevent unauthorized software execution during the device boot sequence. In +case a malware takes control of the boot sequence, sensitive data, services and +network can be impacted. + +The AHAB authentication is based on public key cryptography in which image +data is signed offline using one or more private keys. The resulting signed +image data is then verified on the i.MX processor using the corresponding +public keys. The public keys are included in the final binary and the SRK +Hash is programmed in the SoC fuses for establishing the root of trust. + +In i.MX8 and i.MX8x families the SCU is responsible to interface with the boot +media, managing the process of loading the firmware and software images in +different partitions of the SoC. The SECO is responsible to authenticate the +images and authorize the execution of them. + +1.1.1 [i.MX 8/8x] The System Control Unit (SCU) +------------------------------------ + +The System Control Unit SCU is a subsystem equipped with a programmable M4 +core, which is responsible to handle the resource allocation, power, clocking, +IO configuration and muxing. + +The SCU is also responsible to interface between the rest of the system. In the +secure boot flow the SCU interfaces with the Security Controller (SECO), +requesting the image authentication. + +The System Control Unit FW (SCFW) is responsible to control all the +functionalities of the SCU. This firmware is distributed in a porting kit form. +Instructions to download the SCFW Porting Kit are available in the Linux BSP +Release Notes. + +Details about SCU can be found in the processors Reference Manual (RM). + +1.1.2 [i.MX 8/8x] The Security Controller (SECO) +------------------------------------- + +The SECO is a M0+ core dedicated to handle the SoC security subsystem. The +controller communicates with SCU domain through a dedicate message unit (MU). + +The SECO has a dedicate ROM which is responsible to initialize low level +security features and to authenticate the SECO firmware previously loaded by +the SCU ROM. + +The SECO firmware provides security services at run-time to different domains +of the SoC, one of these being the capability of authenticate images. + +The SECO firmware is signed and distributed by NXP and is always authenticated +in OEM open and closed configuration, instructions to download the SECO FW are +available in the Linux BSP Release Notes. + +Details about SECO can be found in the processors Security Reference Manual +(SRM). + +1.1.3 [i.MX 8ULP/9x] The Edgelock secure enclave +------------------------------------- + +EdgeLock™ Secure Enclave is the security subsystem based on a dedicated core +(RISC-V) to manage security tasks with a tight control on security resources +along with other enhancements. + +The secure enclave has a dedicate ROM which is responsible to initialize low +level security features and to authenticate the secure enclave firmware +previously loaded by the boot management core. + +The secure enclave firmware provides security services at run-time to different + domains of the SoC, one of these being the capability of authenticate images. + +The secure enclave firmware is signed and distributed by NXP and is always +authenticated in OEM open and closed configuration, instructions to download +this FW are available in the Linux BSP Release Notes. + +Details about Edgelock secure enclave can be found in the processors Security +Reference Manual (SRM). + +NOTE: The terms Sentinel, S400, and EdgeLock secure enclave (ELE), and ELE +are used interchangeably throughout the document. + +1.2 The image container +------------------------ + +Due to the new architecture, multiple firmwares and software are required to +boot AHAB supporting devices. In order to store all the images in a single +binary the container image structure is used. + +At least two containers are needed for the boot process, the first container +must include only the Security Subsystem FW (SECO/ELE FW provided by NXP). +Additional containers can contain one or multiple images, depending on the +users specific application. + +The final binary is generated by the imx-mkimage tool. + +1.3 The i.MX8/8x secure boot flow +---------------------------------- + +As mentioned in the introduction, due to the multiple cores architecture the +i.MX8 boot sequence involves SCU ROM, SCFW, SECO ROM, and SECO FW. + +The diagram below illustrate the secure boot flow overview: + +System Controller │ Security Controller │ Cortex-M │ Cortex-A + (SCU) │ (SECO) │ │ + │ │ │ + ╔═════════════╗ │ ╔═════════════╗ ┌───────────┐ ┌─────────┐ + ║ SCU INIT ║ │ ║ SECO INIT ║ │ │ │ │ │ │ + ╚══════╤══════╝ │ ╚══════╤══════╝ │ │ v │ │ v + │ │ │ │ │ ┌──────────┐ │ │ ┌────────────┐ + ╔══════╧══════╗ │ │ │ │ │ Start M4 │ │ │ │ Start AP │ + ║Load SECO FW ║ │ │ │ │ │ IMG │ │ │ │ IMG │ + ╚══════╤══════╝ │ ╔══════╧══════╗ │ │ └──────────┘ │ │ └─────┬──────┘ + ├──────────────>║Auth SECO FW ║ │ │ │ │ │ + ╔══════╧══════╗ │ ╚══════╤══════╝ │ │ ┌────────────┘ │ │ + ║ Load SCU FW ║ │ │ │ │ │ │ │ + ║ and DCD ║ │ │ │ │ │ │ ┌─────┴──────┐ + ╚══════╤══════╝ │ ┌──────┴──────┐ │ │ │ │ │ Load │ + ├──────────────>│ Auth SCU FW │ │ │ │ │ │ Add AP IMG │ + │ │ │ and DCD │ │ │ │ │ └─────┬──────┘ + ╔══════╧══════╗ │ └──────┬──────┘ │ │ │ │ │ + ║ Run DCD ║<──────────────┤ │ │ │ │ │ + ╚══════╤══════╝ │ │ │ │ │ ┌───────────────┤ + │ │ │ │ │ │ │ │ │ + ╔══════╧══════╗ │ │ │ │ │ │ │ │ + ║ Load M4 IMG ║ │ │ │ │ │ │ │ │ + ╚══════╤══════╝ │ ┌──────┴──────┐ │ │ │ │ │ │ + ├──────────────>│ Auth M4 IMG │ │ │ │ │ │ │ + ╔══════╧══════╗ │ └──────┬──────┘ │ │ │ │ │ ┌─────┴──────┐ + ║ Load AP IMG ║ │ │ │ │ │ │ │ │ Run │ + ╚══════╤══════╝ │ ┌──────┴──────┐ │ │ │ │ │ │ Add AP IMG │ + ├──────────────>│ Auth AP IMG │ │ │ │ │ │ └────────────┘ + ╔══════╧══════╗ │ └─────────────┘ │ │ │ │ │ + ║Start SCU FW ║ │ ┌──────────────────┘ │ │ │ │ + ╚══════╤══════╝ │ │ │ │ │ │ + │ │ │ ┌─────────────────────┘ │ │ + ┌──────┴──────┐ │ │ │ │ │ │ + │ Start M4 ├──────┘ │ ┌──────────────────────┘ │ + └──────┬──────┘ │ │ │ │ │ + │ │ │ │ │ │ + ┌──────┴──────┐ │ │ │ │ │ + │ Start AP ├──────────┘ │ │ │ + └─────────────┘ │ │ │ │ + ┌───────────────────────┘ │ │ + │ │ │ │ + v │ │ │ + ┌─────────────┐ │ ┌─────────────┐ │ │ + │Request SECO ├───────>│ Auth AP IMG │ │ │ + └─────────────┘ │ └─────────────┘ │ │ + │ │ │ + + +Notes: +All boxes enclosed by double dash (═) are performed at SCU/SECO ROM level. + +The sequence below explains the i.MX8 and i.MX8x boot flow: + +1 - At reset, the SCU ROM and SECO ROM both start execution. +2 - The SCU ROM reads the boot configuration and loads the SECO FW (First + container) from the boot media to the SECO TCM. +3 - A message is sent by the SCU ROM via MU requesting the SECO ROM to + authenticate the SECO FW which is signed using NXP key. +4 - The SCU ROM loads the second container from the boot media, this container + must contain at least the SCFW which is signed using the OEM keys. +5 - The SCU ROM loads the SCFW to the SCU TCM, a message is sent via MU + requesting the SECO FW to authenticate the SCFW and DCD table. +6 - The SCU ROM configures the DDR and loads the M4 and AP images included in + the second container to their respective load addresses. +7 - The SCU ROM request the SECO FW to authenticate the M4 image. +8 - The SCU ROM request the SECO FW to authenticate the AP image. This image + is the initial AP core software, depending in the U-Boot target it can + be the U-Boot and ATF or only SPL. +9 - The SCFW is initialized and starts the ARM Cortex-M and Cortex-A cores. +10 - From this point additional containers can be loaded by Cortex-M and + Cortex-A cores and authenticated by SECO, the AP SW must interface with + SCU by calling the sc_misc_seco_authenticate() API function. In current + U-Boot implementation the additional image can be the Linux Kernel binary + or the U-Boot proper and ATF. Details about current U-Boot implementation + can be found in AHAB guides included in doc/imx/ahab/guides/ directory. + +1.4 The i.MX 8ULP/9x secure boot flow +---------------------------------- + +The secure boot sequence involves multiple cores booting up at same time and +Edgelock secure enclave ensure authentication of any boot software being loaded. + +The diagram below illustrate the secure boot flow overview for dual boot +scenario in i.MX 8ULP: + + + Cortex-M(CM) │ Edgelock Secure │ Cortex-A(CA) │ uPower(uP) + │ Enclave(ELE) │ │ + │ │ │ │ │ │ │ + ┌┬─────┴─────┬┐ │ ┌┬─────┴─────┬┐ │ │ │ ┌┬─────┴─────┬┐ + ││ INIT ││ │ ││ INIT ││ │ │ │ ││ INIT ││ + └┴─────┬─────┴┘ │ └┴─────┬─────┴┘ │ │ │ └┴─────┬─────┴┘ + │ │ │ │ ┌┬─────┴─────┬┐ │ │ + ┌┬─────┴─────┬┐ │ │ │ ││Load CA FW ││ ┌──────┐ │ + ││Load uP FW ││ │ │ │ └┴─────┬─────┴┘ ││ │ │ + └┴─────┬─────┴┘ │ │ │ │ ││ ┌┬──v──┴─────┬┐ + │ │ ┌┬─────┴─────┬┐ │┌────────┤ ││ ││Load &Start││ + ├─────────────>├│Auth uP FW ││ ││ │ ││ ││ uP FW ││ + │ │ └┴─────┬─────┴┘ ││ │ ││ └┴───────────┴┘ + ┌┬─────┴─────┬┐ │ │ ││ │ ││ + ││Load CM FW││ │ ├────────────────────┼────────┘│ + └┴─────┬─────┴┘ │ │ ││ │ │ + │ │ ┌┬─────┴─────┬┐ ││ │ │ + ├─────────────>├│Auth CM FW ││ ││ ┌┬─────┴─────┬┐ │ + │ │ └┴─────┬─────┴┘ ││ ││Start CA FW││ │ + ┌┬─────┴─────┬┐ │ │ ││ └┴─────┬─────┴┘ │ + ││Load ELE FW││ │ │ ││ │ │ + └┴─────┬─────┴┘ │ │ ││ │ │ + │ │ ┌┬─────┴─────┬┐ ││ │ │ + ├─────────────>├│Auth ELE FW││ ││ │ │ + │ │ └┴─────┬─────┴┘ ││ ┌┬─────┴─────┬┐ │ + ┌┬─────┴─────┬┐ │ │ ││ ││ Load SPL ││ │ + ││Start CM FW││ │ │ ││ └┴─────┬─────┴┘ │ + └┴─────┬─────┴┘ │ │ ││ │ │ + │ │ ┌┬─────┴─────┬┐ ││ ┌────┤ │ + │ │ ││Auth CA FW │┤<───┘ │ │ │ + │ │ └┴─────┬─────┴┘ │ │ │ │ + │ │ │ │ │ │ │ + │ │ ┌┬─────┴─────┬┐ │ │ │ │ + │ │ ││ Auth SPL │┤<───────┘ │ │ + │ │ └┴─────┬─────┴┘ │ │ │ + │ │ ├─────────────────┐ │ │ + │ │ │ │ │ │ │ + │ │ │ │ ┌┬──v──v─────┬┐ │ + │ │ │ │ ││ Run SPL ││ │ + │ │ │ │ └┴───────────┴┘ │ + + +The diagram below illustrate the secure boot flow overview for single boot +scenario in i.MX 9x: + + + Cortex-A(CA) │ Edgelock Secure │ Cortex-M(CM) + │ Enclave(ELE) │ + │ │ │ │ │ + ┌┬─────┴─────┬┐ │ ┌┬─────┴─────┬┐ │ │ + ││ INIT ││ │ ││ INIT ││ │ │ + └┴─────┬─────┴┘ │ └┴─────┬─────┴┘ │ │ + │ │ │ │ ┌┬─────┴─────┬┐ + │ │ │ │┌>││ INIT ││ + │ │ │ ││ └┴─────┬─────┴┘ + ┌┬─────┴─────┬┐ │ │ ││ | + ││Load ELE FW││─────────────>│ ││ │ + └┴─────┬─────┴┘ | | |│ | + │ │ ┌┬─────┴─────┬┐ ││ ┌┬─────┴─────┬┐ + │ │ ├│Auth ELE FW││ ││ ││Start CM FW││ + │ │ └┴─────┬─────┴┘ ││ └┴─────┬─────┴┘ + | | | |│ | + ┌┬─────┴─────┬┐ │ │ ││ │ + ││Load CM FW││ │ | ││ │ + └┴─────┬─────┴┘ │ │ ││ │ + │ │ ┌┬─────┴─────┬┐ ││ │ + ├─────────────>├│Auth CM FW ││ ││ │ + │ │ └┴─────┬─────┴┘ ││ │ + | │ │ ││ │ + │ │ |───────────┘ │ + ┌┬─────┴─────┬┐ │ │ │ │ + ││Load CA FW││ │ │ │ │ + └┴─────┬─────┴┘ │ │ │ │ + │ │ ┌┬─────┴─────┬┐ │ │ + ├─────────────>├│Auth CA FW││ │ │ + │ │ └┴─────┬─────┴┘ │ │ + ┌┬─────┴─────┬┐ │ │ │ │ + ││Start CA FW││ │ | │ │ + └┴─────┬─────┴┘ │ │ │ │ + | │ │ │ │ + | │ │ │ │ + | │ │ │ │ + +More details on the boot flow can be found in respective Security Reference +Manual (SRM). + + +2. Generating a PKI tree +------------------------- + +The first step is to generate the private keys and public keys certificates. +The AHAB architecture is based on a Public Key Infrastructure (PKI) tree. + +The Code Signing Tools package contains an OpenSSL based key generation script +under keys/ directory. The ahab_pki_tree.sh script generates a PKI tree +containing 4 Super Root Keys (SRK), possible to also include a subordinate +SGK key. + +The AHAB supports both RSA and ECC keys, a new PKI tree can be generated by +following the example below: + +- Generating a P384 ECC PKI tree on CST (starting from v3.1.0): + + $ ./ahab_pki_tree.sh + ... + Do you want to use an existing CA key (y/n)?: n + Do you want to use Elliptic Curve Cryptography (y/n)?: y + Enter length for elliptic curve to be used for PKI tree: + Possible values p256, p384, p521: p384 + Enter the digest algorithm to use: sha384 + Enter PKI tree duration (years): 5 + Do you want the SRK certificates to have the CA flag set? (y/n)?: n + +The diagram below illustrate the PKI tree generated: + + ┌─────────┐ + │ CA │ + └────┬────┘ + │ + │ + ┌───────────────┬────────┴────────┬───────────────┐ + │ │ │ │ + │ │ │ │ + v v v v + ┌────────┐ ┌────────┐ ┌────────┐ ┌────────┐ + │ SRK1 │ │ SRK2 │ │ SRK3 │ │ SRK4 │ + └────────┘ └────────┘ └────────┘ └────────┘ + +2.1 Generating a PKI tree including a subordinate SGK key +---------------------------------------------------------- + +The ahab_pki_tree.sh script is also able to generate a PKI tree containing a +subordinate key of the SRK, this key can be used to verify the signature +included in the final signed image. + +Users should set the CA flag when generating the SRK certificates. + +- Generating a P384 ECC PKI tree with a subordinate SGK key on CST (starting +from v3.1.0): + + $ ./ahab_pki_tree.sh + ... + Do you want to use an existing CA key (y/n)?: n + Do you want to use Elliptic Curve Cryptography (y/n)?: y + Enter length for elliptic curve to be used for PKI tree: + Possible values p256, p384, p521: p384 + Enter the digest algorithm to use: sha384 + Enter PKI tree duration (years): 5 + Do you want the SRK certificates to have the CA flag set? (y/n)?: y + +The diagram below illustrate the PKI tree generated: + + ┌─────────┐ + │ CA │ + └────┬────┘ + │ + │ + ┌───────────────┬────────┴────────┬───────────────┐ + │ │ │ │ + v v v v + ┌────────┐ ┌────────┐ ┌────────┐ ┌────────┐ + │ SRK1 │ │ SRK2 │ │ SRK3 │ │ SRK4 │ + └────┬───┘ └───┬────┘ └────┬───┘ └───┬────┘ + │ │ │ │ + v v v v + ┌────────┐ ┌────────┐ ┌────────┐ ┌────────┐ + │ SGK1 │ │ SGK2 │ │ SGK3 │ │ SGK4 │ + └────────┘ └────────┘ └────────┘ └────────┘ + +2.2 Generating a SRK Table and SRK Hash +---------------------------------------- + +The next step is to generated the SRK Table and its respective SRK Table Hash +from the SRK public key certificates created in one of the steps above. + +In the AHAB architecture, the SRK Table is included in the signed image and the +SRK Hash is programmed in the SoC SRK_HASH[511:0]/SRK_HASH[255:0] fuses. + +On the target device during the authentication process the AHAB code verify the +SRK Table against the SoC SRK_HASH fuses, in case the verification is successful +the root of trust is established and the AHAB code can progress with the image +authentication. + +The srktool can be used to generate the SRK Table and its respective SRK +Table Hash. + +- Generating SRK Table and SRK Hash in Linux 64-bit machines: + - In i.MX 8/8x family, the expected SRK HASH is of 512 bit. + $ cd ../crts/ + $ ../linux64/bin/srktool -a -s sha384 -t SRK_1_2_3_4_table.bin \ + -e SRK_1_2_3_4_fuse.bin -f 1 -c \ + SRK1_sha384_secp384r1_v3_usr_crt.pem,\ + SRK2_sha384_secp384r1_v3_usr_crt.pem,\ + SRK3_sha384_secp384r1_v3_usr_crt.pem,\ + SRK4_sha384_secp384r1_v3_usr_crt.pem + + - In i.MX 8ULP/9x, the expected SRK HASH is of 256 bit. + $ cd ../crts/ + $ ../linux64/bin/srktool -a -d sha256 -s sha384 -t SRK_1_2_3_4_table.bin \ + -e SRK_1_2_3_4_fuse.bin -f 1 -c \ + SRK1_sha384_secp384r1_v3_usr_crt.pem,\ + SRK2_sha384_secp384r1_v3_usr_crt.pem,\ + SRK3_sha384_secp384r1_v3_usr_crt.pem,\ + SRK4_sha384_secp384r1_v3_usr_crt.pem + + Regenerate the SRK HASH (SRK_1_2_3_4_fuse.bin) by using SHA256 with + SRK_1_2_3_4_table.bin. + $ openssl dgst -binary -sha256 SRK_1_2_3_4_table.bin + + + +- Optionally users can check if the sha512sum/sha256sum of SRK_1_2_3_4_table +matches with the SRK_1_2_3_4_fuse.bin: + + $ od -t x4 --endian=big SRK_1_2_3_4_fuse.bin + 0000000 01b04697 0253376b 2066fe56 aaef9a91 + 0000020 e62e09d8 14fb7e36 d5b38d05 0982edab + 0000040 7ada6576 2f6b4f59 1fd9347e 46e7305d + 0000060 46e34bf0 89780bd1 c809e714 a17e2f4e + + $ sha512sum SRK_1_2_3_4_table.bin + 01b046970253376b2066fe56aaef9a91\ + e62e09d814fb7e36d5b38d050982edab\ + 7ada65762f6b4f591fd9347e46e7305d\ + 46e34bf089780bd1c809e714a17e2f4e\ + SRK_1_2_3_4_table.bin + +NOTE: The commands above cannot be used as reference to program the SoC + SRK_HASH fuses. + +The SRK_1_2_3_4_table.bin and SRK_1_2_3_4_fuse.bin files can be used in further +steps as explained in AHAB guides available under doc/imx/ahab/guides/ +directory. + +3 Known limitations +---------------------------------------- + +- Due to a limitation in i.MX8QXP B0 silicon it's not possible to use RSA +4096-bit SRK keys with an additional subordinate SGK key. -- 2.55.0