Date: Tue, 12 Jun 2012 19:43:05 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>,
        linuxppc-dev@lists.ozlabs.org, lkml <linux-kernel@vger.kernel.org>,
        michael@ellerman.id.au, antonb@thinktux.localdomain,
        Paul Mackerras <paulus@samba.org>, benh@kernel.crashing.org,
        Ingo Molnar <mingo@elte.hu>, peterz@infradead.org,
        Jim Keniston <jkenisto@us.ibm.com>
Subject: Re: [PATCH v2 1/2] uprobes: Pass probed vaddr to
	arch_uprobe_analyze_insn()
Message-ID: <20120612174305.GA16349@redhat.com>
References: <20120608093257.GG13409@in.ibm.com> <20120611161215.GA12116@redhat.com> <20120612165404.GB30555@linux.vnet.ibm.com>
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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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