Re: [RFC PATCH 08/12] riscv: dynamic (zicfiss) shadow call stack support

Sami Tolvanen
2024-04-11T17:06:17Z

Hi Deepak,

Thanks for the patches!

On Tue, Apr 9, 2024 at 6:12 AM Deepak Gupta <debug@rivosinc.com> wrote:
>
> Adding support for dynamic shadow call stack on riscv. zicfiss ISA extn.
> enables protection for shadow stack against stray writes. This patch
> enables scs_* macros to use zicfiss shadow stack pointer (CSR_SSP) instead
> of relying on `gp`.

CONFIG_DYNAMIC_SCS implies that runtime patching is used to select
between software SCS and an alternative hardware implementation (in
arm64's case, PAC instead of hardware shadow stacks). I understand
this series is still an RFC, but I didn't see runtime patching
support. Are you planning on implementing this later?

If there's no plan to actually patch between Zicfiss and SCS at
runtime, CONFIG_DYNAMIC_SCS doesn't seem like the appropriate choice
and we might need a separate config option that still allows you to
reuse most of the software SCS code.

Sami