linux-kernel - Re: [PATCH] signal: Extend exec

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Date:   Wed, 1 Apr 2020 19:05:59 -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>, Marco Elver <elver@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        kasan-dev <kasan-dev@...glegroups.com>
Subject: Re: [PATCH] signal: Extend exec_id to 64bits

On Wed, Apr 1, 2020 at 6:36 PM Jann Horn <jannh@...gle.com> wrote:
>
> Since the read is already protected by the tasklist_lock, an
> alternative might be to let the execve path also take that lock to
> protect the sequence number update,

No.

tasklist_lock is aboue the hottest lock there is in all of the kernel.

We're not doing stupid things for theoretical issues.

Stop this crazy argument.

A comment - sure. 64-bit atomics or very expensive locks? Not a chance.

                   Linus