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From: Daniel Micay <>
To: Andy Lutomirski <>
Cc: Dave Hansen <>,
	Dave Hansen <>,
	kernel list <>,
	Thomas Gleixner <>,
	Ingo Molnar <>, Borislav Petkov <>,
	"H . Peter Anvin" <>, X86 ML <>,
	Peter Zijlstra <>,
	Michael Ellerman <>,
	Will Deacon <>,
	Andy Lutomirski <>,
Subject: Re: [PATCH 1/2] x86/pkeys: copy pkey state at fork()
Date: Fri, 26 Oct 2018 18:56:21 -0400	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Fri, 26 Oct 2018 at 18:12, Andy Lutomirski <> wrote:
> > On Oct 26, 2018, at 2:39 PM, Daniel Micay <> wrote:
> >
> > I ended up working around this with a pthread_atfork handler disabling
> > my usage of the feature in the child process for the time being. I
> > don't have an easy way to detect if the bug is present within a
> > library so
> Can you not just make sure that the fix is backported to all relevant kernels?

There are too many different distribution kernels and I won't be in
control of where the software is used.

> I suppose we could add a new flag for pkey_get() or something.

That would work, since I can apply the workaround (disabling the
feature in child processes) if I get EINVAL. The flag wouldn't need to
do anything, just existing and being tied to this patch so I have a
way to detect that I can safely use MPK after fork.

> > I'm going to need a kernel version check with a table of
> > kernel releases fixing the problem for each stable branch.
> That won’t work right on district kernels. Please don’t go there.

If it's backported to an earlier version, it will just mean missing a
chance to use it. I'm not going to assume that it behaves a certain
way based on having an old kernel, but rather I just won't use it in a
forked child on an older kernel version if I don't have a way to
detect the problem. It's for a few different uses in library code so
I can't have a runtime test trying to detect it with clone(...). I'd
definitely prefer a proper way to detect that I can use it after fork. I really
don't want to have a hack like that which is why I'm bringing it up.

  reply	other threads:[~2018-10-26 22:56 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-26 19:51 Dave Hansen
2018-10-26 19:51 ` [PATCH 2/2] x86/selftests/pkeys: fork() to check for state being preserved Dave Hansen
2018-10-26 19:59 ` [PATCH 1/2] x86/pkeys: copy pkey state at fork() Dave Hansen
2018-10-26 21:39   ` Daniel Micay
2018-10-26 22:12     ` Andy Lutomirski
2018-10-26 22:56       ` Daniel Micay [this message]
2018-10-29  6:36         ` Ingo Molnar
2018-10-29  8:55           ` Daniel Micay
2018-11-20 21:14   ` Kees Cook
2019-01-09  0:56     ` Kees Cook

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