linux-hardening - Re: [PATCH v8 0/4] Introduce mseal

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Date: Fri, 2 Feb 2024 16:18:07 -0500
From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Jeff Xu <jeffxu@...omium.org>, Jeff Xu <jeffxu@...gle.com>,
        Jonathan Corbet <corbet@....net>, akpm@...ux-foundation.org,
        keescook@...omium.org, jannh@...gle.com, sroettger@...gle.com,
        willy@...radead.org, gregkh@...uxfoundation.org,
        usama.anjum@...labora.com, rdunlap@...radead.org, jorgelo@...omium.org,
        groeck@...omium.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-mm@...ck.org,
        pedro.falcato@...il.com, dave.hansen@...el.com,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH v8 0/4] Introduce mseal

* Linus Torvalds <torvalds@...ux-foundation.org> [240202 15:37]:
> On Fri, 2 Feb 2024 at 11:32, Theo de Raadt <deraadt@...nbsd.org> wrote:
> >
> > Unix system calls must be atomic.
> >
> > They either return an error, and that is a promise they made no changes.
> 
> That's actually not true, and never has been.

...

> 
> In the specific case of mseal(), I suspect there are very few reasons
> ever *not* to be atomic, so in this particular context atomicity is
> likely always something that should be guaranteed. But I just wanted
> to point out that it's most definitely not a black-and-white issue in
> the general case.

There will be a larger performance cost to checking up front without
allowing the partial completion.  I don't expect these to be high, but
it's something to keep in mind if we are okay with the flexibility and
less atomic operation.

Thanks,
Liam