Revision as of 14:29, 2 October 2019 by Registered User
1. Purpose[edit source]
The STM32 header is a STMicroelectronics header needed by ROM code and by TF-A
2. Description[edit source]
Each bootloaders binary image (signed or not) includes a specific STM32 header added on top of the binary data. The header includes the authentication information.
| Name | Length | Byte Offset | Description |
|---|---|---|---|
| Magic number | 32 bits | 0 | 4 bytes in big endian: 'S', 'T', 'M', 0x32 = 0x53544D32 |
| Image Signature | 512 bits | 4 | ECDSA signature for image authentication1 |
| Image Checksum | 32 bits | 68 | Checksum of the payload2 |
| Header version | 32 bits | 72 | Header version v1.0 = 0x00010000 Byte0: reserved Byte1:major version = 0x01 Byte2: minor version = 0x00 Byte3: reserved |
| Image Length | 32 bits | 76 | Length of image in bytes3 |
| Image Entry Point | 32 bits | 80 | Entry point of image |
| Reserved1 | 32 bits | 84 | Reserved |
| Load address | 32 bits | 88 | Load address of image4 |
| Reserved2 | 32 bits | 92 | Reserved |
| Version Number | 32 bits | 96 | Image Version (monotonic number)5 |
| Option flags | 32 bits | 100 | b0=1: no signature verification6 |
| ECDSA Algorithm | 32 bits | 104 | 1: P-256 NIST ; 2: brainpool 256 |
| ECDSA Public key | 512 bits | 108 | ECDSA public key to be used to verify the signature.7 |
| Padding | 84 Bytes | 172 | Reserved padding bytes8. Must all be set to 0 |
| BinaryType | 1 Byte | 255 | Used to check the binary type 0x00: U-Boot 0x10-0x1F: TF-A 0x20-0X2F: OPTEE 0x30: Copro |
- 1 Signature is calculated from first byte of header version field to last byte of image given by image length field.
- 2 32-bit sum of all payload bytes accessed as 8-bit unsigned numbers, discarding any overflow bits. Used to check the downloaded image integrity when signature is not used (if b0=1 in Option flags).
- 3 Length is the length of the built image, it does not include the length of the STM32 header.
- 4 This field is used by ROM code for specific executable images.
- 5 Image version is an anti rollback monotonic counter. The ROM code checks that it is higher or equal to the monotonic counter stored in OTP.
- 6 Enabling signature verification is mandatory on secure closed chips.
- 7 Hash of (algorithm+pubKey) is stored in OTP.
- 8 This padding forces Header size to 0x100 bytes.