Re: [RFC PATCH v1 2/2] mseal: allow noop mprotect

[Kees Cook]

On Wed, Mar 12, 2025 at 03:50:40PM +0000, Lorenzo Stoakes wrote:
> What about madvise() with MADV_DONTNEED on a r/o VMA that's not faulted in?
> That's a no-op right? But it's not permitted.

Hmm, yes, that's a good example. Thank you!

> So now we have an inconsistency between the two calls.

Yeah, I see your concern now.

> I don't know what you mean by 'ergonomic'?

I was thinking about idempotent-ness. Like, some library setting up a
memory region, it can't call its setup routine twice if the second time
through (where no changes are made) it gets rejected. But I think this
is likely just a userspace problem: check for the VMAs before blindly
trying to do it again. (This is strictly an imagined situation.)

> My reply seemed to get truncated at the end here :) So let me ask again -
> do you have a practical case in mind for this?

Sorry, I didn't have any reply to that part, so I left it off. If Jeff
has a specific case in mind, I'll let him answer that part. :)

-Kees

-- 
Kees Cook