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From: Jan Kratochvil <jan.kratochvil@redhat.com>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Alan Stern <stern@rowland.harvard.edu>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	Ingo Molnar <mingo@elte.hu>,
	Maneesh Soni <maneesh@linux.vnet.ibm.com>,
	Prasad <prasad@linux.vnet.ibm.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/2] ptrace/x86: simplify ptrace_write_dr7()
Date: Sun, 14 Apr 2013 21:30:21 +0200	[thread overview]
Message-ID: <20130414193021.GA20962@host2.jankratochvil.net> (raw)
In-Reply-To: <20130414191205.GA28791@redhat.com>

On Sun, 14 Apr 2013 21:12:05 +0200, Oleg Nesterov wrote:
> 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.

I do not understand how these functions map to the PTRACE_* syscall.

But this was a regression from the application point of view as some
application did/do:
	* waitpid - get the process to: t (tracing stop)
	* PTRACE_POKEUSER DR7, enableDR0
	* PTRACE_POKEUSER DR0, address
	* PTRACE_CONT

This was perfectly valid before, there is no "default" addr == 0 used for any
debugging.  Just the applications did not care about PTRACE_POKEUSER ordering.
This is also how the bug was found.


Thanks,
Jan

  parent reply	other threads:[~2013-04-14 19:30 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-04-14 19:12 [PATCH 0/2] ptrace/x86: simplify ptrace_write_dr7() Oleg Nesterov
2013-04-14 19:12 ` [PATCH 1/2] ptrace/x86: simplify the "disable" logic in ptrace_write_dr7() Oleg Nesterov
2013-04-16  0:03   ` Frederic Weisbecker
2013-04-14 19:12 ` [PATCH 2/2] ptrace/x86: dont delay perf_event_disable() till second pass " Oleg Nesterov
2013-04-16  0:44   ` Frederic Weisbecker
2013-04-16 13:30     ` Oleg Nesterov
2013-04-16 22:00       ` Frederic Weisbecker
2013-04-17 12:40         ` Oleg Nesterov
2013-04-14 19:30 ` Jan Kratochvil [this message]
2013-04-14 19:40   ` [PATCH 0/2] ptrace/x86: simplify ptrace_write_dr7() Oleg Nesterov
2013-04-15 23:36 ` Frederic Weisbecker
2013-04-16 13:25   ` Oleg Nesterov
2013-04-17  4:57     ` Jan Kratochvil

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