linux-kernel - Re: [RFC/PATCH] ARM: smp: Fix cpu_up() racing with sys

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:	Wed, 29 Aug 2012 00:24:02 -0700
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	linux-arm-kernel@...ts.infradead.org
CC:	linux-kernel@...r.kernel.org
Subject: Re: [RFC/PATCH] ARM: smp: Fix cpu_up() racing with sys_reboot

On 8/21/2012 9:03 PM, Stephen Boyd wrote:
> Nothing stops a process from hotplugging in a CPU concurrently
> with a sys_reboot() call. In such a situation we could have
> ipi_cpu_stop() mark a cpu as 'offline' and _cpu_up() ignore the
> fact that the CPU is not really offline and call the
> CPU_UP_PREPARE notifier. When this happens stop_machine code will
> complain that the cpu thread already exists and BUG_ON().
>
> CPU0                      CPU1
>
> sys_reboot()
>  kernel_restart()
>   machine_restart()
>    machine_shutdown()
>     smp_send_stop()
>     ...                   ipi_cpu_stop()
>                            set_cpu_online(1, false)
>                             local_irq_disable()
>                              while(1)
>     <PREEMPT>
> cpu_up()
>  _cpu_up()
>    if (!cpu_online(1))
>     __cpu_notify(CPU_UP_PREPARE...)
>
> cpu_stop_cpu_callback()
>   BUG_ON(stopper->thread)
>
> This is easily reproducible by hotplugging in and out in a tight
> loop while also rebooting.
>
> Since the CPU is not really offline and hasn't gone through the
> proper steps to be marked as such, let's mark the CPU as inactive.
> This is just as easily testable as online and avoids any possibility
> of _cpu_up() trying to bring the CPU back online when it never was
> offline to begin with.
>
> Signed-off-by: Stephen Boyd <sboyd@...eaurora.org>
> ---
>
> Perhaps we can take the hotplug lock in the sys_reboot() case but I
> don't think that actually fixes everything. For example, in cases
> where machine_shutdown() is called from emergency_restart() we would
> have to take the hotplug lock which doesn't really seem feasible.

Any comments on this patch?

-- 
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.

--
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/