Re: [PATCH] rtc: armada38x: add __ro_after_init to armada38x_rtc_ops

[Russell King - ARM Linux]

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@xxxxxxxxxxxxxxx> 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.

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