linux-kernel - Re: [PATCH 01/17] x86, fpu: wrap get_xsave

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Message-ID: <5511F65A.5020505@intel.com>
Date:	Tue, 24 Mar 2015 16:42:18 -0700
From:	Dave Hansen <dave.hansen@...el.com>
To:	Andy Lutomirski <luto@...capital.net>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	X86 ML <x86@...nel.org>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Rik van Riel <riel@...hat.com>,
	Suresh Siddha <sbsiddha@...il.com>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Fenghua Yu <fenghua.yu@...el.com>
Subject: Re: [PATCH 01/17] x86, fpu: wrap get_xsave_addr() to make it safer

On 03/24/2015 03:28 PM, Andy Lutomirski wrote:
> Your function appears to be getting it for write (I assume that's what
> the unlazy_fpu is for), so I'd rather have it called
> tsk_get_xsave_field_for_write or something like that.

It should be entirely read-only.

For MPX (the only user of get_xsave_addr() iirc), we are only worried
about getting the status codes (and addresses) out of the bndstatus
register and making sure that the kernel-recorded bounds directory
address matches the bndcfgu (configuration) register.

We don't ever write to the registers.
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