linux-kernel - Re: [PATCH] Fix devmem_is_allowed for below 1MB accesses for an efi machine

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Message-ID: <20121003043116.GA26241@srcf.ucam.org>
Date:	Wed, 3 Oct 2012 05:31:17 +0100
From:	Matthew Garrett <mjg@...hat.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	T Makphaibulchoke <tmac@...com>, tglx@...utronix.de,
	mingo@...hat.com, x86@...nel.org, akpm@...ux-foundation.org,
	yinghai@...nel.org, tiwai@...e.de, viro@...iv.linux.org.uk,
	aarcange@...hat.com, tony.luck@...el.com, mgorman@...e.de,
	weiyang@...ux.vnet.ibm.com, octavian.purdila@...el.com,
	paul.gortmaker@...driver.com, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH] Fix devmem_is_allowed for below 1MB accesses for an
 efi machine

On Tue, Oct 02, 2012 at 02:50:09PM -0700, H. Peter Anvin wrote:

> That sounds like exactly the opposite of normal /dev/mem behavior... we
> allow access to non-memory resources (which really could do anything if
> misused), but not memory.

>From arch/x86/mm/init.c:

 * On x86, access has to be given to the first megabyte of ram because that area
 * contains bios code and data regions used by X and dosemu and similar apps.

Limiting this to just RAM would be safer than it currently is. I'm not 
convinced that there's any good reason to allow *any* access down there 
for EFI systems, though.

-- 
Matthew Garrett | mjg59@...f.ucam.org
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