linux-kernel - Re: [PATCH] rtc: armada38x: add __ro_after_init to armada38x_rtc

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Message-ID: <20170103213118.GM14217@n2100.armlinux.org.uk>
Date:   Tue, 3 Jan 2017 21:31:18 +0000
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Kees Cook <keescook@...omium.org>
Cc:     Bhumika Goyal <bhumirks@...il.com>,
        Julia Lawall <julia.lawall@...6.fr>,
        Jason Cooper <jason@...edaemon.net>, andrew@...n.ch,
        gregory.clement@...e-electrons.com,
        sebastian.hesselbarth@...il.com, a.zummo@...ertech.it,
        alexandre.belloni@...e-electrons.com,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>, rtc-linux@...glegroups.com,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] rtc: armada38x: add __ro_after_init to armada38x_rtc_ops

On Tue, Jan 03, 2017 at 01:18:29PM -0800, Kees Cook wrote:
> On Mon, Jan 2, 2017 at 6:06 AM, Russell King - ARM Linux
> <linux@...linux.org.uk> wrote:
> > On Mon, Dec 26, 2016 at 05:01:02PM +0530, Bhumika Goyal wrote:
> >> The object armada38x_rtc_ops of type rtc_class_ops structure is not
> >> modified after getting initialized by armada38x_rtc_probe. Apart from
> >> getting referenced in init it is also passed as an argument to the function
> >> devm_rtc_device_register but this argument is of type const struct
> >> rtc_class_ops *. Therefore add __ro_after_init to its declaration.
> >
> > What I'd prefer here is for the structure to be duplicated, with one
> > copy having the alarm methods and one which does not.  Both can then
> > be made "const" (so placed into the read-only section at link time)
> > and the probe function select between the two.
> >
> > I think that's a cleaner and better solution, even though it's
> > slightly larger.
> >
> > I'm not a fan of __ro_after_init being used where other solutions are
> > possible.
> 
> Can the pointer that points to the struct rtc_class_ops be made ro_after_init?

It's passed into the RTC core code, and probably stored in some dynamically
allocated object, so probably no.  It's the same class of problem as every
file_operations pointer in the kernel, or the thousand other operations
structure pointers that a running kernel has.

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