linux-kernel - Re: [patch 2/4] jump_label: Fix concurrency issues in static_key_slow

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20240610175756.GU8774@noisy.programming.kicks-ass.net>
Date: Mon, 10 Jun 2024 19:57:56 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: LKML <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Sam Sun <samsun1006219@...il.com>, x86@...nel.org,
	syzkaller-bugs@...glegroups.com, xrivendell7@...il.com
Subject: Re: [patch 2/4] jump_label: Fix concurrency issues in
 static_key_slow_dec()

On Mon, Jun 10, 2024 at 02:46:36PM +0200, Thomas Gleixner wrote:

> @@ -247,20 +247,25 @@ EXPORT_SYMBOL_GPL(static_key_disable);
>  
>  static bool static_key_slow_try_dec(struct static_key *key)
>  {
> +	int v;
>  
>  	/*
> +	 * Go into the slow path if key::enabled is less than or equal than
> +	 * one. One is valid to shut down the key, anything less than one
> +	 * is an imbalance, which is handled at the call site.
> +	 *
> +	 * That includes the special case of '-1' which is set in
> +	 * static_key_slow_inc_cpuslocked(), but that's harmless as it is
> +	 * fully serialized in the slow path below. By the time this task
> +	 * acquires the jump label lock the value is back to one and the
> +	 * retry under the lock must succeed.

Harmless yes, but it really should not happen to begin with. If this
happens it means someone wants to disable a key that is in the middle of
getting enabled for the first time.

I'm tempted to want a WARN here instead. Hmm?

>  	 */
> +	v = atomic_read(&key->enabled);
> +	do {
> +		if (v <= 1)
> +			return false;
> +	} while (!likely(atomic_try_cmpxchg(&key->enabled, &v, v - 1)));
> +
>  	return true;
>  }