Re: [PATCH RFT v5 4/7] fork: Add shadow stack support to clone3()

On Fri, Feb 09, 2024 at 08:18:11PM +0000, Edgecombe, Rick P wrote:

On Sat, 2024-02-03 at 00:05 +0000, Mark Brown wrote:

...

+       if (write_user_shstk_64((u64 __user *)addr, 0)) +               return false;

+       return true; +}

So, don't we want to consume the token on the *new* task's MM, which was already duplicated but still unmapped? In which case I think the other arch's would need to GUP regardless of the existence of shadow stack atomic ops.

Yes, that would be better - if nothing else it allows reuse of the same shadow stack for multiple !CLONE_VM clone3()s.

I wonder about adding a shstk_post_fork() to make it easier to think about and maintain, even if there are no issues today.

I agree.