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Re: [PATCH v1 RFC Zisslpcfi 1/9] target/riscv: adding zimops and zisslpc

From: Richard Henderson
Subject: Re: [PATCH v1 RFC Zisslpcfi 1/9] target/riscv: adding zimops and zisslpcfi extension to RISCV cpu config
Date: Wed, 15 Feb 2023 18:20:11 -1000
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.7.1

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.


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