linux-kernel - Re: [PATCH v10 07/12] task_isolation: add debug boot flag

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: <56D7537B.5040804@mellanox.com>
Date:	Wed, 2 Mar 2016 15:56:27 -0500
From:	Chris Metcalf <cmetcalf@...lanox.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Gilad Ben Yossef <giladb@...hip.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>, Tejun Heo <tj@...nel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Christoph Lameter <cl@...ux.com>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Andy Lutomirski <luto@...capital.net>,
	<linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH v10 07/12] task_isolation: add debug boot flag

On 3/2/2016 3:37 PM, Peter Zijlstra wrote:
> On Wed, Mar 02, 2016 at 03:09:31PM -0500, Chris Metcalf wrote:
>> +void task_isolation_debug(int cpu)
>> +{
>> +	struct task_struct *p;
>> +
>> +	if (!task_isolation_possible(cpu))
>> +		return;
>> +
>> +	rcu_read_lock();
>> +	p = cpu_curr(cpu);
>> +	get_task_struct(p);
> As I think Oleg keeps reminding me, this is not actually a safe thing to
> do.

So what's the right solution?  The fast path in task_isolation_debug_task basically
just uses the new "task_isolation_flags", and "pid" and "comm".  I would think those
would all have to be safe because of the get_task_struct().

The piece that might be problematic is the eventual call to send_sig_info() using the
task_struct pointer (called via task_isolation_debug_task -> task_isolation_interrupt).
Clearly this is safe at some level, since that's more or less what sys_kill() does and the
process could similarly evaporate half way through sending the signal.

Suggestions?  Thanks!

-- 
Chris Metcalf, Mellanox Technologies
http://www.mellanox.com