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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Wed, 1 Apr 2020 16:55:42 -0700
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Subject: Re: [PATCH] signal: Extend exec_id to 64bits
To:     Jann Horn <jannh@google.com>
Cc:     "Eric W. Biederman" <ebiederm@xmission.com>,
        Alan Stern <stern@rowland.harvard.edu>,
        Andrea Parri <parri.andrea@gmail.com>,
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        David Howells <dhowells@redhat.com>,
        Jade Alglave <j.alglave@ucl.ac.uk>,
        Luc Maranget <luc.maranget@inria.fr>,
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On Wed, Apr 1, 2020 at 4:51 PM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> It's literally testing a sequence counter for equality. If you get
> tearing in the high bits on the write (or the read), you'd still need
> to have the low bits turn around 4G times to get a matching value.

Put another way: first you'd have to work however many weeks to do 4
billion execve() calls, and then you need to hit basically a
single-instruction race to take advantage of it.

Good luck with that. If you have that kind of God-like capability,
whoever you're attacking stands no chance in the first place.

                  Linus