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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Andrea Arcangeli <aarcange@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>, Jann Horn <jannh@google.com>,
	Daniel Colascione <dancol@google.com>,
	Pavel Emelyanov <xemul@virtuozzo.com>,
	Lokesh Gidra <lokeshgidra@google.com>,
	Nick Kralevich <nnk@google.com>, Nosh Minwalla <nosh@google.com>,
	Tim Murray <timmurray@google.com>,
	Mike Rapoport <rppt@linux.vnet.ibm.com>,
	Linux API <linux-api@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 3/7] Add a UFFD_SECURE flag to the userfaultfd API.
Date: Wed, 23 Oct 2019 16:15:12 -0400
Message-ID: <CAHk-=wgC-RGcTOrtY+ZQLdZ74EULBvD_+uiPToqhAAMNjAHM6g@mail.gmail.com> (raw)
In-Reply-To: <20191023190959.GA9902@redhat.com>

On Wed, Oct 23, 2019 at 3:10 PM Andrea Arcangeli <aarcange@redhat.com> wrote:
>
> That wouldn't break the ABI, no more than when if you boot a kernel
> built with CONFIG_USERFAULTFD=n.

What? No.

You're entirely incorrect.

If USEFAULTFD no longer works, and if people depend on it, then it's
breaking the ABI. End of story. No weaselwording of "as if built with
CONFIG_USERFAULTFD=n" allowed, no garbage.

Btw, the whole "breaking the ABI" is misleading wording anyway. It's
irrelevant. You can "break" the ABI all you want by changing
semantics, adding or removing features, or making it do anything else
- as long as nobody notices.

Because the only thing that matters is that it doesn't break any user
workflows. That's _all_ that matters, but it's a big deal, and it
means that your fantasy reading of what "ABI" means is irrelevant.
Just because there's a config option to turn something off, doesn't
mean that you can then claim that you can do whatever.

So your statement is nonsensical and pointless.

Please don't spread this kind of bogus claims.

                Linus

  parent reply index

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-12 19:15 [PATCH 0/7] Harden userfaultfd Daniel Colascione
2019-10-12 19:15 ` [PATCH 1/7] Add a new flags-accepting interface for anonymous inodes Daniel Colascione
2019-10-14  4:26   ` kbuild test robot
2019-10-14 15:38   ` Jann Horn
2019-10-14 18:15     ` Daniel Colascione
2019-10-14 18:30       ` Jann Horn
2019-10-15  8:08   ` Christoph Hellwig
2019-10-12 19:15 ` [PATCH 2/7] Add a concept of a "secure" anonymous file Daniel Colascione
2019-10-14  3:01   ` kbuild test robot
2019-10-15  8:08   ` Christoph Hellwig
2019-10-12 19:15 ` [PATCH 3/7] Add a UFFD_SECURE flag to the userfaultfd API Daniel Colascione
2019-10-12 23:10   ` Andy Lutomirski
2019-10-13  0:51     ` Daniel Colascione
2019-10-13  1:14       ` Andy Lutomirski
2019-10-13  1:38         ` Daniel Colascione
2019-10-14 16:04         ` Jann Horn
2019-10-23 19:09           ` Andrea Arcangeli
2019-10-23 19:21             ` Andy Lutomirski
2019-10-23 21:16               ` Andrea Arcangeli
2019-10-23 21:25                 ` Andy Lutomirski
2019-10-23 22:41                   ` Andrea Arcangeli
2019-10-23 23:01                     ` Andy Lutomirski
2019-10-23 23:27                       ` Andrea Arcangeli
2019-10-23 20:05             ` Daniel Colascione
2019-10-24  0:23               ` Andrea Arcangeli
2019-10-23 20:15             ` Linus Torvalds [this message]
2019-10-24  9:02             ` Mike Rapoport
2019-10-24 15:10               ` Andrea Arcangeli
2019-10-25 20:12                 ` Mike Rapoport
2019-10-22 21:27         ` Daniel Colascione
2019-10-23  4:11         ` Andy Lutomirski
2019-10-23  7:29           ` Cyrill Gorcunov
2019-10-23 12:43             ` Mike Rapoport
2019-10-23 17:13               ` Andy Lutomirski
2019-10-12 19:15 ` [PATCH 4/7] Teach SELinux about a new userfaultfd class Daniel Colascione
2019-10-12 23:08   ` Andy Lutomirski
2019-10-13  0:11     ` Daniel Colascione
2019-10-13  0:46       ` Andy Lutomirski
2019-10-12 19:16 ` [PATCH 5/7] Let userfaultfd opt out of handling kernel-mode faults Daniel Colascione
2019-10-12 19:16 ` [PATCH 6/7] Allow users to require UFFD_SECURE Daniel Colascione
2019-10-12 23:12   ` Andy Lutomirski
2019-10-12 19:16 ` [PATCH 7/7] Add a new sysctl for limiting userfaultfd to user mode faults Daniel Colascione
2019-10-16  0:02 ` [PATCH 0/7] Harden userfaultfd James Morris
2019-11-15 15:09 ` Stephen Smalley

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