Re: [REGRESSION] secretmem: SIGBUS on memfd_secret() pages while perf record runs

[Sasha Levin]

On Sat, Oct 03, 2026 at 10:18:34AM +0100, Lorenzo Stoakes (ARM) wrote:
> On Fri, Oct 02, 2026 at 09:30:23PM -0400, Sasha Levin wrote:
> > > Since commit 97d34aa65c29 ("mm/secretmem: properly account locked
> > > pages"), in v7.3-rc2 and the 6.18.52 and 7.2.5 backports, touching a
> > > memfd_secret() page for the first time fails with SIGBUS while the
> > > same user is running perf record, and read() into such a page fails
> >
> > Thanks for the report. I've dropped 97d34aa65c29 from the 6.12 queue,
> > and also removed the copies that were staged for 6.6 and 6.1.
> >
> > 7.2.y and 6.18.y already shipped it, so those need an upstream fix,
> > which stable will pick up once it lands.
>
> Sasha,
>
> Could we perhaps take a breath and pause?

I pulled this out quickly because I didn't want this issue to go into the kernels that were released this morning.

In general, our policy around this type of reports is that if the issue is in a
released LTS kernel, we will wait for a fix upstream, and if the issue is still
in our queues, we will simply drop the patch from the queue.

> This patch fixes a really quite serious vulnerability that allows an
> unprivileged process to allocate arbitrary, unreclaimable (i.e. OOMK cannot
> save you) memory.
>
> Allow me to assess the validity of this report _before_ dropping things
> from queues perhaps? :)

No disagreement that this would have been better - in this case it was timing
as the releases were about to happen the following day, so the safest choice
was to drop it while we figure it out.

> It was sent late on Friday in a week that I was ill and it's Saturday
> pre-LPC, so that's hardly a timeframe that I could reasonably have replied.

Keep in mind that our release cycles are fairly short, so this shouldn't be too
big of a deal?

We will generally go for the safe option of dropping a commit that introduces a
regression as it's fairly easy to queue it back up very soon after a
diagnosis/fix shows up.

--
Thanks,
Sasha