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93 lines
4.0 KiB
Markdown
93 lines
4.0 KiB
Markdown
#TREZOR Core Bootloader
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Bootloader code is split into two stages. See [Memory Layout](memory.md) for more info about in which sectors the code is stored.
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First stage checks the integrity and signatures of second stage and runs it if everything is OK.
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However, if first stage bootloader finds a valid second stage bootloader on the SD card (in raw format, no filesystem), it will replace the internal second stage, allowing an upgrade of the second stage.
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First stage is stored in write-protected area, which means only upgrade of the second stage bootloader is allowed.
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##Common notes
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* Hash function used is SHA-256 and signature system is Ed25519 (allows combining signatures by multiple keys into one).
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* All multibyte integer values are little endian.
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##Bootloader Format
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TREZOR Core (second stage) bootloader consists of 2 parts:
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1. bootloader header
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2. bootloader code
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###Bootloader Header
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Total length of bootloader header is 256 bytes.
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| offset | length | name | description |
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|-------:|-------:|------|-------------|
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| 0x0000 | 4 | magic | firmware magic `TRZB` |
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| 0x0004 | 4 | hlen | length of the bootloader header |
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| 0x0008 | 4 | expiry | valid until timestamp (0=infinity) |
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| 0x000C | 4 | codelen | length of the bootloader code |
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| 0x0010 | 1 | vmajor | version (major) |
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| 0x0011 | 1 | vminor | version (minor) |
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| 0x0012 | 1 | vpatch | version (patch) |
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| 0x0013 | 1 | vbuild | version (build) |
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| 0x0014 | 1 | slsigidx | SatoshiLabs signature indexes (bitmap) |
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| 0x0015 | 64 | slsig | SatoshiLabs signature |
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| 0x0079 | 135 | reserved | not used yet |
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##Firmware Format
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TREZOR Core firmware consists of 3 parts:
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1. vendor header
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2. firmware header
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3. firmware code
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###Vendor Header
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Total length of vendor header is 82 + 32 * (number of pubkeys) + (length of vendor string) + (length of vendor image) bytes rounded up to the closest multiply of 256 bytes.
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| offset | length | name | description |
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|-------:|-------:|------|-------------|
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| 0x0000 | 4 | magic | firmware magic `TRZV` |
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| 0x0004 | 4 | hlen | length of the vendor header |
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| 0x0008 | 4 | expiry | valid until timestamp (0=infinity) |
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| 0x000C | 1 | vsig_m | number of signatures needed to run the firmware from this vendor |
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| 0x000D | 1 | vsig_n | number of pubkeys vendor wants to use for signing |
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| 0x000E | 2 | reserved | not used yet |
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| 0x0010 | 32 | vpub1 | vendor pubkey 1 |
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| ... | ... | ... | ... |
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| ? | 32 | vpubn | vendor pubkey n |
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| ? | 1 | vstr_len | vendor string length |
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| ? | ? | vstr | vendor string |
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| ? | ? | vimg | vendor image (in [TOIf format](toif.md)) |
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| ? | 1 | slsigidx | SatoshiLabs signature indexes (bitmap) |
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| ? | 64 | slsig | SatoshiLabs signature |
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###Firmware Header
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Total length of firmware header is 256 bytes.
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| offset | length | name | description |
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|-------:|-------:|------|-------------|
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| 0x0000 | 4 | magic | firmware magic `TRZF` |
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| 0x0004 | 4 | hlen | length of the firmware header |
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| 0x0008 | 4 | expiry | valid until timestamp (0=infinity) |
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| 0x000C | 4 | codelen | length of the firmware code |
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| 0x0010 | 1 | vmajor | version (major) |
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| 0x0011 | 1 | vminor | version (minor) |
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| 0x0012 | 1 | vpatch | version (patch) |
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| 0x0013 | 1 | vbuild | version (build) |
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| 0x0014 | 1 | vndsigidx | vendor signature indexes (bitmap) |
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| 0x0015 | 64 | vndsig | vendor signature |
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| 0x0079 | 135 | reserved | not used yet |
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##Various ideas
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* Bootloader should be able to read vendor+firmware header and send info about FW to client in features message.
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* Bootloader should not try to run firmware if there is not any.
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* Storage wiping rule: Don't erase storage when old FW and new FW are signed using the same key set. Otherwise erase.
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* Bootloader should send error to client when firmware update fails and allow client to try one more time. This prevents storage area erasure by accident.
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