linux-kernel - Re: [patch 08/11] Modify Ptrace routines to access breakpoint registers

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Message-Id: <20090312031449.83F34FC3B6@magilla.sf.frob.com>
Date:	Wed, 11 Mar 2009 20:14:49 -0700 (PDT)
From:	Roland McGrath <roland@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	prasad@...ux.vnet.ibm.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Alan Stern <stern@...land.harvard.edu>
Subject: Re: [patch 08/11] Modify Ptrace routines to access breakpoint
	registers

> 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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