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Date: Wed, 1 Apr 2020 16:55:42 -0700
From: Linus Torvalds <>
To: Jann Horn <>
Cc: "Eric W. Biederman" <>, Alan Stern <>, 
	Andrea Parri <>, Will Deacon <>, 
	Peter Zijlstra <>, Boqun Feng <>, 
	Nicholas Piggin <>, David Howells <>, 
	Jade Alglave <>, Luc Maranget <>, 
	"Paul E. McKenney" <>, Akira Yokosawa <>, 
	Daniel Lustig <>, Adam Zabrocki <>, 
	kernel list <>, 
	Kernel Hardening <>, Oleg Nesterov <>, 
	Andy Lutomirski <>, Bernd Edlinger <>, 
	Kees Cook <>, Andrew Morton <>, 
	stable <>
Subject: Re: [PATCH] signal: Extend exec_id to 64bits

On Wed, Apr 1, 2020 at 4:51 PM Linus Torvalds
<> 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.


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