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

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Message-ID: <20090310144002.GF3850@elte.hu>
Date:	Tue, 10 Mar 2009 15:40:02 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	prasad@...ux.vnet.ibm.com
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Roland McGrath <roland@...hat.com>
Subject: Re: [patch 08/11] Modify Ptrace routines to access breakpoint
	registers


* prasad@...ux.vnet.ibm.com <prasad@...ux.vnet.ibm.com> wrote:

> -static unsigned long debugreg_addr_limit(struct task_struct *task)
> -{
> -#ifdef CONFIG_IA32_EMULATION
> -	if (test_tsk_thread_flag(task, TIF_IA32))
> -		return IA32_PAGE_OFFSET - 3;
> -#endif
> -	return TASK_SIZE_MAX - 7;
> -}
> -

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.

For example a hardware breakpoint can be at 0xbfffffff with a 
length of 4 bytes - thus overlapping into kernel-space by 3 
bytes. It is important to not let that happen.

	Ingo
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