linux-kernel - Re: [PATCH 6/7] uprobes: Fix uprobe_copy

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Message-ID: <20121006095258.GD9145@linux.vnet.ibm.com>
Date:	Sat, 6 Oct 2012 15:22:58 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <peterz@...radead.org>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Anton Arapov <anton@...hat.com>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/7] uprobes: Fix uprobe_copy_insn() race with itself

* Oleg Nesterov <oleg@...hat.com> [2012-09-30 21:42:24]:

> install_breakpoint() is called under mm->mmap_sem, this protects
> set_swbp() but not uprobe_copy_insn(). Two or more different tasks
> can call install_breakpoint()->uprobe_copy_insn() at the same time,
> this leads to numerous problems if UPROBE_COPY_INSN is not set.
> 
> Just for example, the second copy_insn() can corrupt the already
> analyzed/fixuped uprobe->arch.insn and race with handle_swbp().
> 
> This patch simply adds uprobe->copy_mutex to serialize this code.
> We could probably reuse ->consumer_rwsem, but this would mean that
> consumer->handler() can not use mm->mmap_sem, not good.
> 
> Note: this is another temporary ugly hack until we move this logic
> into uprobe_register().
> 
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>

Given that we copy just for the first install, and register not being  a
performance path, Can we use a single mutex instead of a per-uprobe
mutex.

Acked-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>

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