68a45490fc
This commit adds the ability to verify that USB DFU updates are correctly signed using ed25519. This required adding support to embassy-boot for reading from the DFU partition.
64 lines
2.7 KiB
Markdown
64 lines
2.7 KiB
Markdown
# Bootloader for STM32
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This bootloader implementation uses `embassy-boot` and `embassy-usb-dfu` to manage firmware updates and interact with the flash memory on STM32WB55 devices.
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## Prerequisites
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- Rust toolchain with `cargo` installed
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- `cargo-flash` for flashing the bootloader
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- `dfu-util` for firmware updates
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- `cargo-binutils` for binary generation
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## Usage
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### 1. Flash the Bootloader
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First, flash the bootloader to your device:
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```
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cargo flash --features embassy-stm32/stm32wb55rg --release --chip STM32WB55RGVx
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```
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### 2. Build and Flash Application
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Generate your application binary and flash it using DFU:
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```
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cargo objcopy --release -- -O binary fw.bin
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dfu-util -d c0de:cafe -w -D fw.bin
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```
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### 3. Sign Updates Before Flashing (Optional)
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Currently, embassy-usb-dfu only supports a limited implementation of the generic support for ed25519-based update verfication in embassy-boot. This implementation assumes that a signature is simply concatenated to the end of an update binary. For more details, please see https://embassy.dev/book/#_verification and/or refer to the documentation for embassy-boot-dfu.
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To sign (and then verify) application updates, you will first need to generate a key pair:
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```
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signify-openbsd -G -n -p secrets/key.pub -s secrets/key.sec
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tail -n1 secrets/key.pub | base64 -d -i - | dd ibs=10 skip=1 > secrets/key.pub.short
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```
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Then you will need to sign all you binaries with the private key:
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```
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cargo objcopy --release -- -O binary fw.bin
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shasum -a 512 -b fw.bin | head -c128 | xxd -p -r > target/fw-hash.txt
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signify-openbsd -S -s secrets/key.sec -m target/fw-hash.txt -x target/fw-hash.sig
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cp fw.bin fw-signed.bin
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tail -n1 target/fw-hash.sig | base64 -d -i - | dd ibs=10 skip=1 >> fw-signed.bin
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dfu-util -d c0de:cafe -w -D fw-signed.bin
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```
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Finally, as shown in this example with the `verify` feature flag enabled, you then need to embed the public key into your bootloader so that it can verify update signatures.
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N.B. Please note that the exact steps above are NOT a good example of how to manage your keys securely. In a production environment, you should take great care to ensure that (at least the private key) is protected and not leaked into your version control system.
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## Troubleshooting
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- Make sure your device is in DFU mode before flashing
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- Verify the USB VID:PID matches your device (c0de:cafe)
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- Check USB connections if the device is not detected
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- Make sure the transfer size option of `dfu-util` matches the bootloader configuration. By default, `dfu-util` will use the transfer size reported by the device, but you can override it with the `-t` option if needed.
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- Make sure `control_buf` size is larger than or equal to the `usb_dfu` `BLOCK_SIZE` parameter (in this example, both are set to 4096 bytes).
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