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From: Borislav Petkov <bp@alien8.de>
To: Seunghun Han <kkamagui@gmail.com>, Tony Luck <tony.luck@intel.com>
Cc: linux-edac@vger.kernel.org, linux-kernel@vger.kernel.org,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: [PATCH] x86: mce: fix kernel panic when check_interval is changed
Date: Fri, 23 Feb 2018 11:42:39 +0100	[thread overview]
Message-ID: <20180223104239.GA4981@pd.tnic> (raw)
In-Reply-To: <20180223101350.8344-1-kkamagui@gmail.com>

On Fri, Feb 23, 2018 at 07:13:50PM +0900, Seunghun Han wrote:
> I am Seunghun Han and a senior security researcher at National Security
> Research Institute of South Korea.
> 
> I found a critical security issue which can make kernel panic in userspace.
> After analyzing the issue carefully, I found that MCE driver in the kernel
> has a problem which can be occurred in SMP environment.
> 
> The check_interval file in
> /sys/devices/system/machinecheck/machinecheck<cpu number> directory is a
> global timer value for MCE polling. If it is changed by one CPU, MCE driver
> in kernel calls mce_restart() function and broadcasts the event to other

Right, so I'm thinking that doing that per-CPU configuration doesn't
make a whole lot of sense. It is not something that needs to happen very
often and it is done globally anyway.

So what we should do here, IMO, is make mce_restart() grab a mutex and
thus serialize all those sysfs writes. It will naturally also slow down
any hammering from userspace which we should not allow anyway.

Tony, what do you think?

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.

WARNING: multiple messages have this Message-ID (diff)
From: Borislav Petkov <bp@alien8.de>
To: Seunghun Han <kkamagui@gmail.com>, Tony Luck <tony.luck@intel.com>
Cc: linux-edac@vger.kernel.org, linux-kernel@vger.kernel.org,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: x86: mce: fix kernel panic when check_interval is changed
Date: Fri, 23 Feb 2018 11:42:39 +0100	[thread overview]
Message-ID: <20180223104239.GA4981@pd.tnic> (raw)

On Fri, Feb 23, 2018 at 07:13:50PM +0900, Seunghun Han wrote:
> I am Seunghun Han and a senior security researcher at National Security
> Research Institute of South Korea.
> 
> I found a critical security issue which can make kernel panic in userspace.
> After analyzing the issue carefully, I found that MCE driver in the kernel
> has a problem which can be occurred in SMP environment.
> 
> The check_interval file in
> /sys/devices/system/machinecheck/machinecheck<cpu number> directory is a
> global timer value for MCE polling. If it is changed by one CPU, MCE driver
> in kernel calls mce_restart() function and broadcasts the event to other

Right, so I'm thinking that doing that per-CPU configuration doesn't
make a whole lot of sense. It is not something that needs to happen very
often and it is done globally anyway.

So what we should do here, IMO, is make mce_restart() grab a mutex and
thus serialize all those sysfs writes. It will naturally also slow down
any hammering from userspace which we should not allow anyway.

Tony, what do you think?

  reply	other threads:[~2018-02-23 10:42 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-02-23 10:13 [PATCH] x86: mce: fix kernel panic when check_interval is changed Seunghun Han
2018-02-23 10:13 ` Seunghun Han
2018-02-23 10:42 ` Borislav Petkov [this message]
2018-02-23 10:42   ` Borislav Petkov
2018-02-23 10:52 ` [PATCH] " Greg Kroah-Hartman
2018-02-23 10:52   ` Greg Kroah-Hartman
2018-02-25 20:05   ` [PATCH] " Seunghun Han
2018-02-25 20:05     ` Seunghun Han
2018-02-28  9:32     ` [PATCH] " Borislav Petkov
2018-02-28  9:32       ` Borislav Petkov
2018-02-28  9:48       ` [PATCH] " Seunghun Han
2018-02-28  9:48         ` Seunghun Han

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