linux-kernel - Re: [PATCH v8 04/10] x86, mpx: hook #BR exception handler to allocate bound tables

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Date:	Wed, 24 Sep 2014 07:40:39 -0700
From:	Dave Hansen <dave.hansen@...el.com>
To:	Qiaowei Ren <qiaowei.ren@...el.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>
CC:	x86@...nel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 04/10] x86, mpx: hook #BR exception handler to allocate
 bound tables

On 09/11/2014 01:46 AM, Qiaowei Ren wrote:
> +/*
> + * When a BNDSTX instruction attempts to save bounds to a BD entry
> + * with the lack of the valid bit being set, a #BR is generated.
> + * This is an indication that no BT exists for this entry. In this
> + * case the fault handler will allocate a new BT.
> + *
> + * With 32-bit mode, the size of BD is 4MB, and the size of each
> + * bound table is 16KB. With 64-bit mode, the size of BD is 2GB,
> + * and the size of each bound table is 4MB.
> + */
> +int do_mpx_bt_fault(struct xsave_struct *xsave_buf)
> +{
> +	unsigned long status;
> +	unsigned long bd_entry, bd_base;
> +
> +	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 + MPX_BD_SIZE_BYTES))
> +		return -EINVAL;
> +
> +	return allocate_bt((long __user *)bd_entry);
> +}

This needs a comment about how we got the address of the bd_entry.
Essentially just note that the hardware tells us where the missing/bad
entry is.

Would there be any value in ensuring that a VMA is present at bd_entry?


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