linux-hardening - Re: [PATCH v10 0/5] Introduce mseal

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Date: Tue, 14 May 2024 16:01:50 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: "Theo de Raadt" <deraadt@...nbsd.org>
Cc: Matthew Wilcox <willy@...radead.org>, Jonathan Corbet <corbet@....net>,
 jeffxu@...omium.org, keescook@...omium.org, jannh@...gle.com,
 sroettger@...gle.com, gregkh@...uxfoundation.org,
 torvalds@...ux-foundation.org, usama.anjum@...labora.com,
 Liam.Howlett@...cle.com, surenb@...gle.com, merimus@...gle.com,
 rdunlap@...radead.org, jeffxu@...gle.com, 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 v10 0/5] Introduce mseal

On Tue, 14 May 2024 16:48:47 -0600 "Theo de Raadt" <deraadt@...nbsd.org> wrote:

> Matthew Wilcox <willy@...radead.org> wrote:
> 
> > > Not taking a position on merging, but I have to ask: are we convinced at
> > > this point that mseal() isn't a chrome-only system call?  Did we ever
> > > see the glibc patches that were promised?
> > 
> > I think _this_ version of mseal() is OpenBSD's mimmutable() with a
> > basically unused extra 'flags' argument.  As such, we have an existance
> > proof that it's useful beyond Chrome.
> 
> Yes, it is close enough.
> 
> > I think Liam still had concerns around the
> > walk-the-vmas-twice-to-error-out-early part of the implementation?
> > Although we can always fix the implementation later; changing the API
> > is hard.
> 
> Yes I am a bit worried about the point Liam brings up -- we've discussed
> it privately at length.  Matthew, to keep it short I have a different
> viewpoint:
> 
> Some of the Linux m* system calls have non-conforming, partial-work-then-return-error
> behaviour.  I cannot find anything like this in any system call in any other
> operating system, and I believe there is a defacto rule against doing this, and
> Linux has an optimization which violating this, and I think it could be fixed
> with fairly minor expense, and can't imagine it affecting a single application.

Thanks.

> I worry that the non-atomicity will one day be used by an attacker.

How might an attacker exploit this?