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

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Date: Thu, 11 Apr 2024 17:05:38 +0000
From: Sami Tolvanen <samitolvanen@...gle.com>
To: Deepak Gupta <debug@...osinc.com>
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	Ard Biesheuvel <ardb@...nel.org>, Will Deacon <will@...nel.org>
Subject: Re: [RFC PATCH 08/12] riscv: dynamic (zicfiss) shadow call stack support

Hi Deepak,

Thanks for the patches!

On Tue, Apr 9, 2024 at 6:12 AM Deepak Gupta <debug@...osinc.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