linux-kernel - Re: [PATCH] PM: core: Do not randomize struct dev_pm

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Date:   Fri, 5 Aug 2022 16:10:29 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux PM <linux-pm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] PM: core: Do not randomize struct dev_pm_ops layout

On Fri, Aug 5, 2022 at 4:12 AM Kees Cook <keescook@...omium.org> wrote:
>
>
>
> On August 4, 2022 10:15:08 AM PDT, "Rafael J. Wysocki" <rjw@...ysocki.net> wrote:
> >From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> >
> >Because __rpm_get_callback() uses offsetof() to compute the address of
> >the callback in question in struct dev_pm_ops, randomizing the layout
> >of the latter leads to interesting, but unfortunately also undesirable
> >results in some cases.
>
> How does this manifest? This is a compile-time randomization, so offsetof() will find the correct location.

Well, I would think so.

> Is struct dev_pm_ops created or consumed externally from the kernel at any point?

I'm not sure TBH.  I have seen a trace where pci_pm_resume_noirq() is
evidently called via rpm_callback() which should never happen if the
offset computation is correct.

The driver in question (which is out of the tree for now) is modular,
so in theory it could be built separately from the rest of the kernel,
but I think that this still should work, shouldn't it?

> >
> >Prevent that from happening by using the __no_randomize_layout
> >annotation on struct dev_pm_ops.
> >
> >Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> >---
> > include/linux/pm.h |    2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> >Index: linux-pm/include/linux/pm.h
> >===================================================================
> >--- linux-pm.orig/include/linux/pm.h
> >+++ linux-pm/include/linux/pm.h
> >@@ -307,7 +307,7 @@ struct dev_pm_ops {
> >       int (*runtime_suspend)(struct device *dev);
> >       int (*runtime_resume)(struct device *dev);
> >       int (*runtime_idle)(struct device *dev);
> >-};
> >+} __no_randomize_layout;
> >
> > #define SYSTEM_SLEEP_PM_OPS(suspend_fn, resume_fn) \
> >       .suspend = pm_sleep_ptr(suspend_fn), \
> >
> >
> >
>
> --
> Kees Cook