linux-kernel - Re: [RFC PATCH 1/3] asm-generic: io: Add exec versions of ioremap

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Message-ID: <20160518175102.GX5783@n2100.arm.linux.org.uk>
Date:	Wed, 18 May 2016 18:51:02 +0100
From:	Russell King - ARM Linux <linux@...linux.org.uk>
To:	Dave Gerlach <d-gerlach@...com>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-omap@...r.kernel.org, Russ Dill <russ.dill@...com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Arnd Bergmann <arnd@...db.de>, Shawn Guo <shawnguo@...nel.org>,
	Tony Lindgren <tony@...mide.com>,
	Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
	Nishanth Menon <nm@...com>
Subject: Re: [RFC PATCH 1/3] asm-generic: io: Add exec versions of ioremap

On Wed, May 18, 2016 at 09:12:20AM -0500, Dave Gerlach wrote:
> Ok thank you for the pointer. I agree, the memremap API looks like a better
> fit for this. I think it likely makes the most sense to still add these
> ioremap_exec and ioremap_exec_nocache and then call them through the
> memremap API based on new flags. This will fit into the current use model
> for memremap as it currently uses all of the other ioremap calls internally,
> and doing it how I just described will let this code evolve along with
> memremap.

I would _really_ prefer not to do that.  Why?  Because IO memory does
not have the required properties to be executable.  IO memory is normally
memory which has side effects - and by side effects, I mean reading it
can provoke hardware to perform some action.  You don't want to be
executing from such memory.

So, in my mind, ioremap_exec makes absolutely no sense, and having it
gives people a new interface to abuse - and abuse they will.

-- 
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