linux-kernel - Re: [PATCH v4 2/3] x86, mpx: hook #BR exception handler to allocate bound tables

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Message-ID: <5306BD8D.3030606@intel.com>
Date:	Fri, 21 Feb 2014 10:44:29 +0800
From:	Ren Qiaowei <qiaowei.ren@...el.com>
To:	Andy Lutomirski <luto@...capital.net>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>
CC:	x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/3] x86, mpx: hook #BR exception handler to allocate
 bound tables

On 02/13/2014 04:19 AM, Andy Lutomirski wrote:
> On 02/12/2014 10:36 AM, Qiaowei Ren wrote:
>> An access to an invalid bound directory entry will cause a #BR
>> exception. This patch hook #BR exception handler to allocate
>> one bound table and bind it with that buond directory entry.
>>
>> This will avoid the need of forwarding the #BR exception
>> to the user space when bound directory has invalid entry.
>>
>> Signed-off-by: Qiaowei Ren <qiaowei.ren@...el.com>
>> ---
>> +void do_mpx_bt_fault(struct xsave_struct *xsave_buf)
>> +{
>> +	unsigned long status;
>> +	unsigned long bd_entry, bd_base;
>> +	unsigned long bd_size = 1UL << (MPX_L1_BITS+MPX_L1_SHIFT);
>> +
>> +	bd_base = xsave_buf->bndcsr.cfg_reg_u & MPX_BNDCFG_ADDR_MASK;
>> +	status = xsave_buf->bndcsr.status_reg;
>> +
>> +	bd_entry = status & MPX_BNDSTA_ADDR_MASK;
>> +	if ((bd_entry >= bd_base) && (bd_entry < bd_base + bd_size))
>> +		allocate_bt(bd_entry);
>> +}
>
> This still just loops on failure, right?
>
Seems like that SIGBUS should be raised if the allocation fail.

	if (!do_mpx_bt_fault(xsave_buf))
		force_sig(SIGBUS, tsk);

Thanks,
Qiaowei

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