linux-kernel - Re: [PATCH 0/1] (Was: Linux 3.11-rc4)

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Date:	Wed, 7 Aug 2013 19:22:08 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Grazvydas Ignotas <notasas@...il.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Felipe Contreras <felipe.contreras@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Denys Vlasenko <dvlasenk@...hat.com>
Subject: Re: [PATCH 0/1] (Was: Linux 3.11-rc4)

On 08/07, Grazvydas Ignotas wrote:
>
> It's not that wine needs all this, it's the Windows games that use
> debug registers to store random values to them for their copy
> protection stuff.

Thanks.

> My wine commits try to sidestep these
> kernel restrictions/sanity checking.

My point was, it seems that starting from 3.11 you can remove both
extra PTRACE_POKEUSER's. Unless, of course, the initial state of dr7
doesn't match dr0 - dr6 set_thread_context() is going to update.

Anyway I agree this interface is very confusing and inconvenient.

And just in case, it is not that I think set_thread_context() should
be changed, I am just wondering whether the kernel still has the bugs
which should be fixed.

> Personally I'd say the kernel should not limit what's written to debug
> registers. Why can't I write insane values to registers in _my_
> hardware? It's not like it's going to break the hardware or anything.

Even if this is safe (and btw I have no idea if this is always true or
not ;), how a user can notice the error then?

Oleg.

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