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doc: Update documentation about syscalls

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- Revise firmware implementation notes
- Document how to do fw syscalls
  - Document how to trigger a syscall function in the firmware, how to
    pass arguments, what the caller is responsible for and what is
    returned.
- Describe hardware syscall implementation
  - how the syscall interrupts are triggered,
  - the hardware privilege escalation,
  - the UDS protection.

Co-authored-by: Daniel Jobson <jobson@tillitis.se>
Co-authored-by: Michael Cardell Widerkrantz <mc@tillitis.se>
This commit is contained in:
Mikael Ågren 2025-02-26 07:03:56 +01:00
parent 7554787678
commit c52442b54c
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GPG key ID: E02DA3D397792C46
4 changed files with 161 additions and 120 deletions
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33
hw/application_fpga/core/tk1/README.md
View file

@ -23,17 +23,6 @@ and version of the device. They can be read by FW as well as
applications.
### Control of execution mode
```
ADDR_APP_MODE_CTRL: 0x08
```
This register controls if the device is executing in FW mode or in App
mode. The register can be written once between power cycles, and only
by FW. If set the device is in app mode.
### Control of RGB LED
```
@ -75,19 +64,7 @@ ADDR_APP_SIZE: 0x0d
These registers provide read only information to the loaded app to
itself - where it was loaded and its size. The values are written by
FW as part of the loading of the app. The registers can't be written
when the `ADDR_APP_MODE_CTRL` has been set.
### Access to Blake2s
```
ADDR_BLAKE2S: 0x10
```
This register provides the 32-bit function pointer address to the
Blake2s hash function in the FW. It is written by FW during boot. The
register can't be written to when the `ADDR_APP_MODE_CTRL` has been
set.
in application mode.
### Access to CDI
@ -99,10 +76,10 @@ ADDR_CDI_LAST: 0x27
These registers provide access to the 256-bit compound device secret
calculated by the FW as part of loading an application. The registers
are written by the FW. The register can't be written to when the
`ADDR_APP_MODE_CTRL` has been set. The CDI is readable by apps, which
can then use it as a base secret for any other secrets required to
carry out their intended use case.
are written by the FW. The register can't be written in application
mode. The CDI is readable by apps, which can then use it as a base
secret for any other secrets required to carry out their intended use
case.
### Access to UDI

3
hw/application_fpga/core/uds/README.md
View file

@ -6,8 +6,7 @@ Unique Device Secret core
This core store and protect the Unique Device Secret (UDS) asset. The
UDS can be accessed as eight separate 32-bit words. The words can only
be accessed as long as the app_mode input is low, implying that the
CPU is executing the FW.
be accessed as long as the `en` input is high.
The UDS words can be accessed in any order, but a given word can only
be accessed once between reset cycles. This read once functionality is