aether

minimal bootloader with bare metal hypervisor on blue pill.

overview

mostly it's a show case of security model. bootloader recieves calls, ensures a loaded app foolows its manifest, handles interrupts and beheaves as a supervisor for app. this includes MPU, stack protection, SVC, and etc.

hypervisor api

SVC calls include:

• region request to a peripheral/memory based on app's manifest
• wdt kick
• exit / fault

this model provides scale for apps. UART, SPI, GPIO and etc. happen as plain MMIO reads once SVC_REGION_REQ has granted the region.

architecture

memory layout (assume stm32f103 - 64k flash and 20k RAM).

1. hypervisor flash - 16K - protected
2. hypervisor's RAM - 4K - privileged
3. GUARD (MPU) - 1 K - no access
4. app flash - 48K
5. app's RAM and stack

isolation model

building

build everything with make all, that includes the modules (modules.mk) and core library.

there are also such commands:

make flash   # to flash bootloader (!)
make erase   # to erase the board
make clean   # to clean build folder
make debug   # run gdb 
make modules # build apps 

# various debugging stuff
make dump-boot
make sym-boot 

no external os or libraries required. the only optional dependency is a ed25519 implementation included as a submodule.