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Message-ID: <CAHk-=wgM3qZeChs_1yFt8p8ye1pOaM_cX57BZ_0+qdEPcAiaCQ@mail.gmail.com>
Date: Wed, 1 Apr 2020 16:55:42 -0700
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Jann Horn <jannh@...gle.com>
Cc: "Eric W. Biederman" <ebiederm@...ssion.com>, Alan Stern <stern@...land.harvard.edu>,
Andrea Parri <parri.andrea@...il.com>, Will Deacon <will@...nel.org>,
Peter Zijlstra <peterz@...radead.org>, Boqun Feng <boqun.feng@...il.com>,
Nicholas Piggin <npiggin@...il.com>, David Howells <dhowells@...hat.com>,
Jade Alglave <j.alglave@....ac.uk>, Luc Maranget <luc.maranget@...ia.fr>,
"Paul E. McKenney" <paulmck@...nel.org>, Akira Yokosawa <akiyks@...il.com>,
Daniel Lustig <dlustig@...dia.com>, Adam Zabrocki <pi3@....com.pl>,
kernel list <linux-kernel@...r.kernel.org>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>, Oleg Nesterov <oleg@...hat.com>,
Andy Lutomirski <luto@...capital.net>, Bernd Edlinger <bernd.edlinger@...mail.de>,
Kees Cook <keescook@...omium.org>, Andrew Morton <akpm@...ux-foundation.org>,
stable <stable@...r.kernel.org>
Subject: Re: [PATCH] signal: Extend exec_id to 64bits
On Wed, Apr 1, 2020 at 4:51 PM Linus Torvalds
<torvalds@...ux-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
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