linux-kernel - Re: what's the replace for the big kernel lock after kernel version 2.6.39 for system call.

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Message-ID: <20111129214136.GR2203@ZenIV.linux.org.uk>
Date:	Tue, 29 Nov 2011 21:41:36 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Wen Yan Xin <WenYan_Xin@...antec.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Zongliang Li <Zongliang_Li@...antec.com>,
	Gang He <Gang_He@...antec.com>,
	Yong Jun Chai <YongJun_Chai@...antec.com>
Subject: Re: what's the replace for the big kernel lock after kernel version
 2.6.39 for system call.

On Mon, Nov 28, 2011 at 01:03:07AM -0800, Wen Yan Xin wrote:
> Hi all,
> 
> I have a trouble of working on kernel 2.6.39 and later. Originally when our kernel module startups, it hooks some file system call, like sys_open... , and the big kernel lock - lock_kernel() - will be held before creating the hook to prevent user application use system calls, and be released after the hook created.
> 
> 
> But after the kernel 2.6.39, the big kernel lock has been removed. I'm thinking there should be one or more lock that should be used. 
> 
> So, my question is which lock should be held now, when we hook the system call of file system?
> 
> I'd really appreciate your answer in advance.

1) your rootkit has always been racy; taking BKL does *NOT* prevent another
CPU from entering a system call.

2) none; just don't do it.
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