linux-kernel - Re: [BACKPORT 4.4.y 01/25] mmc: pwrseq: constify mmc_pwrseq

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Date:   Tue, 26 Mar 2019 09:11:44 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     "# 3.4.x" <stable@...r.kernel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Janusz Krzysztofik <jmkrzyszt@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        "Tobin C. Harding" <me@...in.cc>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Julia Lawall <Julia.Lawall@...6.fr>,
        linux-mmc <linux-mmc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [BACKPORT 4.4.y 01/25] mmc: pwrseq: constify mmc_pwrseq_ops structures

On Tue, Mar 26, 2019 at 2:22 AM Greg KH <gregkh@...uxfoundation.org> wrote:
> On Fri, Mar 22, 2019 at 04:43:52PM +0100, Arnd Bergmann wrote:

> >  }
> >
> > -static struct mmc_pwrseq_ops mmc_pwrseq_simple_ops = {
> > +static const struct mmc_pwrseq_ops mmc_pwrseq_simple_ops = {
> >       .pre_power_on = mmc_pwrseq_simple_pre_power_on,
> >       .post_power_on = mmc_pwrseq_simple_post_power_on,
> >       .power_off = mmc_pwrseq_simple_power_off,
>
> Why is this needed for a stable patch?  It doesn't fix a bug, it just
> looks like it is a "nice thing" to have, right?  I don't think any later
> patch in this series relies it it, or am I missing something?

Right, the benefit here is rather small. In theory, any structure of
function pointers is a place into which an exploit can be placed
in case someone finds a way to modify a few bytes of kernel
memory. Placing the structures in read-only memory make this
a little harder (it doesn't prevent rowhammer attacks though).

Dropping this patch is certainly fine with me, as we have a large
supply of other structure definitions like this, and we wont' get close to
plugging enough of them in stable kernels.

       Arnd