linux-kernel - Re: [PATCH 0/2] ptrace/x86: simplify ptrace_write

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Message-ID: <20130416132545.GA9189@redhat.com>
Date:	Tue, 16 Apr 2013 15:25:45 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Ingo Molnar <mingo@...e.hu>,
	Jan Kratochvil <jan.kratochvil@...hat.com>,
	Maneesh Soni <maneesh@...ux.vnet.ibm.com>,
	Prasad <prasad@...ux.vnet.ibm.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] ptrace/x86: simplify ptrace_write_dr7()

On 04/16, Frederic Weisbecker wrote:
>
> On Sun, Apr 14, 2013 at 09:12:05PM +0200, Oleg Nesterov wrote:
>
> Looking at the bug report, it seems they only reproduced with a homemade
> test. No real app has reported that issue?

iirc (Jan can correct me) gdb hit this problem, but it was already
changed to change DR0 first.

> > Jan, Frederic, et all. What do you think we should do?
> >
> > 	1. Change ptrace_write_dr7() to do register_user_hw_breakpoint()
> > 	   if necessary.
> >
> > 	   This is what I was going to do, but I am no longer sure
> > 	   we want this. For what? Unlikely it is very useful to use
> > 	   the "default" addr == 0 for debugging.
>
> So you mean assume that the addr is 0 in dr[0-3] if we write dr7 before writing
> the addr register?

Yes,

> Yes, I'm convinced that's the right direction!

OK. Thanks Jan and Frederic.

I'll send v2 tomorrow with the 3rd patch which adds _register into
write_dr7. Plus another minor/offtopic fix I forgot to send.

Oleg.

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