linux-kernel - Re: [PATCH v22 1/4] mm: add MAP_DROPPABLE for designating always lazily freeable mappings

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <ZpA9zMmjmsFbevuO@zx2c4.com>
Date: Thu, 11 Jul 2024 22:17:16 +0200
From: "Jason A. Donenfeld" <Jason@...c4.com>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: David Hildenbrand <david@...hat.com>, linux-kernel@...r.kernel.org,
	patches@...ts.linux.dev, tglx@...utronix.de,
	linux-crypto@...r.kernel.org, linux-api@...r.kernel.org,
	x86@...nel.org, Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Adhemerval Zanella Netto <adhemerval.zanella@...aro.org>,
	Carlos O'Donell <carlos@...hat.com>,
	Florian Weimer <fweimer@...hat.com>, Arnd Bergmann <arnd@...db.de>,
	Jann Horn <jannh@...gle.com>,
	Christian Brauner <brauner@...nel.org>,
	David Hildenbrand <dhildenb@...hat.com>, linux-mm@...ck.org
Subject: Re: [PATCH v22 1/4] mm: add MAP_DROPPABLE for designating always
 lazily freeable mappings

On Thu, Jul 11, 2024 at 10:07:30PM +0200, Jason A. Donenfeld wrote:
> Hi Linus,
> 
> On Thu, Jul 11, 2024 at 10:57:17AM -0700, Linus Torvalds wrote:
> > May I suggest a slightly different approach: do what we did for "pte_mkwrite()".
> > 
> > It needed the vma too, for not too dissimilar reasons: special dirty
> > bit handling for the shadow stack. See
> 
> Thanks for the suggestion. That seems pretty clean.
> 
> It still needs to avoid setting swapbacked in the first place, but
> ensuring that it's never dirty means it won't get turned back on.
> 
> The first patch renames pte_dirty() to pte_dirty_novma(). The second
> patch adds an inline function, pte_dirty(pte, vma) that just forwards
> the pte to pte_dirty_novma(), and then converts callers that have a vma
> available to pass to call pte_dirty(). And then the VM_DROPPABLE patch
> simply adds the `&& !(vma->vm_flags & VM_DROPPABLE)` condition to
> pte_dirty().
> 
> I put these in https://git.zx2c4.com/linux-rng/log/ per usual, and I'll
> post a new version to the list not before long (unless objections).

Oh, I didn't catch upthread in time (my mail flow is based on `lei
up`, which I guess I should run at greater frequency). It seems like we
apparently might go in a different direction.

I'll move that to https://git.zx2c4.com/linux-rng/log/?h=jd/pte_dirty in
case it's useful later, though.

Jason