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From: Roland McGrath <roland@redhat.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: prasad@linux.vnet.ibm.com, Andrew Morton <akpm@linux-foundation.org>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Alan Stern <stern@rowland.harvard.edu>
Subject: Re: [patch 08/11] Modify Ptrace routines to access breakpoint
	registers
In-Reply-To: Ingo Molnar's message of  Tuesday, 10 March 2009 15:40:02 +0100 <20090310144002.GF3850@elte.hu>
References: <20090305043440.189041194@linux.vnet.ibm.com>
	<20090305044051.GI17747@in.ibm.com>
	<20090310144002.GF3850@elte.hu>
Message-Id: <20090312031449.83F34FC3B6@magilla.sf.frob.com>
Date: Wed, 11 Mar 2009 20:14:49 -0700 (PDT)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1277
Lines: 33

> I dont see where this security check has been carried over into 
> the generic code. The new code has:
> 
>  +int arch_check_va_in_userspace(unsigned long va, struct task_struct *tsk)
>  +{
>  +       return (va < TASK_SIZE);
>  +}
> 
> but i think that misses the detail that it's not just the start 
> address of an x86 breakpoint that has to be considered, but also 
> the end addess of it.

It also needs to be TASK_SIZE_OF(tsk), which is shorthand for the same
logic already in the 64-bit debugreg_addr_limit().  

For the end-of-range issue, it perhaps ought to check size-1 instead of
wordsize-1, i.e. through the end of the actual breakpoint range, not of the
word containing it.  What debugreg_addr_limit() does is the historical
ptrace check on x86, but I don't see a reason to disallow a 1-byte
watchpoint on the last addressable user-space byte if the hardware will
support it.

So either the arch check should take a size parameter, or the
arch-independent code can just call it with address+size-1.


Thanks,
Roland
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