linux-kernel - Re: [RFC PATCH 1/2] Fix: sched/membarrier: p->mm->membarrier

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: <1969212687.1583.1567610796694.JavaMail.zimbra@efficios.com>
Date:   Wed, 4 Sep 2019 11:26:36 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     paulmck <paulmck@...ux.ibm.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Oleg Nesterov <oleg@...hat.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        "Russell King, ARM Linux" <linux@...linux.org.uk>,
        Chris Metcalf <cmetcalf@...hip.com>,
        Chris Lameter <cl@...ux.com>, Kirill Tkhai <tkhai@...dex.ru>,
        Mike Galbraith <efault@....de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: [RFC PATCH 1/2] Fix: sched/membarrier: p->mm->membarrier_state
 racy load

----- On Sep 4, 2019, at 7:49 AM, Peter Zijlstra peterz@...radead.org wrote:

> On Wed, Sep 04, 2019 at 01:28:19PM +0200, Peter Zijlstra wrote:
>> @@ -196,6 +198,17 @@ static int membarrier_register_global_expedited(void)
>>  		 */
>>  		smp_mb();
>>  	} else {
>> +		struct task_struct *g, *t;
>> +
>> +		read_lock(&tasklist_lock);
>> +		do_each_thread(g, t) {
>> +			if (t->mm == mm) {
>> +				atomic_or(MEMBARRIER_STATE_GLOBAL_EXPEDITED,
>> +					  &t->membarrier_state);
>> +			}
>> +		} while_each_thread(g, t);
>> +		read_unlock(&tasklist_lock);
>> +
>>  		/*
>>  		 * For multi-mm user threads, we need to ensure all
>>  		 * future scheduler executions will observe the new
> 
> Arguably, because this is exposed to unpriv users and a potential
> preemption latency issue, we could do it in 3 passes:
> 
>	- RCU, mark all found lacking, count
>	- RCU, mark all found lacking, count
>	- if count of last pass, tasklist_lock
> 
> That way, it becomes much harder to trigger the bad case.
> 
> Do we worry about that?

Allowing unprivileged processes to iterate over all processes/threads
with the tasklist lock held is something I try to avoid.

Thanks,

Mathieu


-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com