linux-kernel - Re: [PATCH -tip v2 2/2] [BUGFIX] kprobes/x86: Check Interrupt Flag modifier when registering probe

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Date:	Fri, 15 Mar 2013 10:10:41 +0530
From:	Ananth N Mavinakayanahalli <ananth@...ibm.com>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Timo Juhani Lindfors <timo.lindfors@....fi>,
	yrl.pp-manager.tt@...achi.com,
	Steven Rostedt <rostedt@...dmis.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH -tip v2 2/2] [BUGFIX] kprobes/x86: Check Interrupt Flag
	modifier when registering probe

On Thu, Mar 14, 2013 at 08:52:43PM +0900, Masami Hiramatsu wrote:
> Currently kprobes check whether the copied instruction modifies
> IF (interrupt flag) on each probe hit. This means not only
> introducing overhead but also involving inat_get_opcode_attribute
> into kprobes hot path, and it can cause an infinit recursive
> call (and kernel panic in the end).
> 
> Actually, since the copied instruction itself never be modified
> on the buffer, it is needless to analyze the instruction every
> probe hit.
> 
> To fix this issue, we checks it only once when registering probe
> and store the result on ainsn->if_modifier.
> 
> Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
> Reported-by: Timo Juhani Lindfors <timo.lindfors@....fi>
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: Ananth N Mavinakayanahalli <ananth@...ibm.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>

Acked-by: Ananth N Mavinakayanahalli <ananth@...ibm.com>

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