linux-kernel - Re: [PATCH 1/2] ARM: PIE infrastructure

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Message-ID: <20160427193941.GR19428@n2100.arm.linux.org.uk>
Date:	Wed, 27 Apr 2016 20:39:41 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>
Cc:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Dave Martin <Dave.Martin@....com>,
	Olof Johansson <olof@...om.net>,
	Doug Anderson <dianders@...omium.org>,
	Heiko Stuebner <heiko@...ech.de>, Russ Dill <Russ.Dill@...com>,
	Nicolas Ferre <nicolas.ferre@...el.com>
Subject: Re: [PATCH 1/2] ARM: PIE infrastructure

On Sat, Apr 23, 2016 at 01:15:03AM +0200, Alexandre Belloni wrote:
> Well, do you want me to iterate and use fncpy on all the functions from
> the generated binary?

No, because that will break the image too.

> I'm not sure this is necessary as the generated binary is self contained
> and doing so will force me to also ensure the offsets are kept the same.
> Doing only one copy is much more convenient. However, I still need to
> ensure the destination address is properly 8-byte aligned and the
> flush_icache_range().

What you need to do is to immitate being an ELF loader - in other words,
copy the blob according to the alignment rules of the blob (which may be
greater than 8-byte alignment) and use the symbol table to find the
functions and the type of the function (ARM vs ELF).

> I understand this is abusing fncpy() but it does want I need (still, I'm
> planning to avoid the BUG() by always passing a properly aligned
> destination address).

Yea yea yea, such arguments don't wash with me, sorry.  The "but it does
what I need" is total bollocks, sorry.  fncpy() is designed for a
purpose, and what you're doing is an abuse of it, one which I will not
stand for for the sake of long term maintainability.

-- 
RMK's Patch system: http://www.arm.linux.org.uk/developer/patches/
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