Re: [PATCH v1 RFC Zisslpcfi 1/9] target/riscv: adding zimops and zisslpcfi extension to RISCV cpu config

[Richard Henderson]

On 2/15/23 15:46, LIU Zhiwei wrote:
> We can rearrange the patch set as follows:
>
> 1. Implement the zimop extension.
>
> 2. Implement the forward cfi only for system mode.
>
> 3. Implement the backward cfi only for system mode.
>
> 4. Carefully make the forward cfi can work on user mode.
>
> 5. Carefully make the backward cfi work for user mode.
>
> I don't think we can easily make cfi  work on user mode. So we can also ignore the 4 or 5, 
> or both.

This is a good ordering.  Similar to how we implemented CFI for AArch64.

I strongly suspect that you will need to defer 5 until the Linux uabi is defined.  It will 
require some mmap bit (MAP_* or PROT_*) which libc will use to define shadow stacks for 
new threads.

But having the system support in means that you can work on the corresponding 
kernel bits.


r~