linux-kernel - Re: [PATCH] fix hrtimer_enqueue

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]

Date:	Tue, 5 Feb 2013 11:44:20 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Izik Eidus <izik.eidus@...ellosystems.com>
cc:	Andrea Arcangeli <aarcange@...hat.com>,
	linux-kernel@...r.kernel.org,
	leonid Shatz <leonid.shatz@...ellosystems.com>
Subject: Re: [PATCH] fix hrtimer_enqueue_reprogram race

On Mon, 4 Feb 2013, Izik Eidus wrote:

> From: leonid Shatz <leonid.shatz@...ellosystems.com>
> 
> it seems like hrtimer_enqueue_reprogram contain a race which could result in
> timer.base switch during unlock/lock sequence.
> 
> See the code at __hrtimer_start_range_ns where it calls
> hrtimer_enqueue_reprogram. The later is releasing lock protecting the timer
> base for a short time and timer base switch can occur from a different CPU
> thread. Later when __hrtimer_start_range_ns calls unlock_hrtimer_base, a base
> switch could have happened and this causes the bug
> 
> Try to start the same hrtimer from two different threads in kernel running
> each one on a different CPU. Eventually one of the calls will cause timer base
> switch while another thread is not expecting it.

Aside of the bug in the hrtimer code being a real one, writing code
which fiddles with the same resource (hrtimer) unserialized is broken
on its own.
 
> This can happen in virtualized environment where one thread can be delayed by
> lower hypervisor, and due to time delay a different CPU is taking care of
> missed timer start and runs the timer start logic on its own.

Without noticing that something else already takes care of it? So
you're saying that the code in question relies on magic serialization
in the hrtimer code. Doesn't look like a brilliant design.

Thanks,

	tglx
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/