linux-kernel - Re: [PATCH v2 1/2] uprobes: Pass probed vaddr to arch_uprobe_analyze

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Date:	Tue, 12 Jun 2012 19:43:05 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	linuxppc-dev@...ts.ozlabs.org, lkml <linux-kernel@...r.kernel.org>,
	michael@...erman.id.au, antonb@...nktux.localdomain,
	Paul Mackerras <paulus@...ba.org>, benh@...nel.crashing.org,
	Ingo Molnar <mingo@...e.hu>, peterz@...radead.org,
	Jim Keniston <jkenisto@...ibm.com>
Subject: Re: [PATCH v2 1/2] uprobes: Pass probed vaddr to
	arch_uprobe_analyze_insn()

On 06/12, Srikar Dronamraju wrote:
> >
> > Note also that we should move this !UPROBE_COPY_INSN from
> > install_breakpoint() to somewhere near alloc_uprobe(). This code
> > is called only once, it looks a bit strange to use the "random" mm
> > (the first mm vma_prio_tree_foreach() finds) and its mapping to
> > verify the insn. In fact this is simply not correct and should be
> > fixed, note that on x86 arch_uprobe_analyze_insn() checks
>
> The reason we "delay" the copy_insn to the first insert is because
> we have to get access to mm. For archs like x86, we want to know if the
> executable is 32 bit or not

Yes. And this is wrong afaics.

Once again. This !UPROBE_COPY_INSN code is called only once, and it
uses the "random" mm. After that install_breakpoint() just calls
set_swbp(another_mm) while the insn can be invalid because
another_mm->ia32_compat != mm->ia32_compat.

> So in effect, if we get access to
> struct file corresponding to the inode and if the inode corresponds to
> 32 bit executable file or 64 bit executable file during register, then
> we can move it around alloc_uprobe().

I don't think this can work. I have another simple fix in mind, I'll
write another email later.

Oleg.

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