linux-kernel - Re: Are read-only static labels incompatible with kernel modules?

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Message-ID: <20201208125129.GY2414@hirez.programming.kicks-ass.net>
Date:   Tue, 8 Dec 2020 13:51:29 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        Marco Elver <elver@...gle.com>, keescook@...omium.org
Subject: Re: Are read-only static labels incompatible with kernel modules?

On Mon, Dec 07, 2020 at 09:37:54PM +0100, Andrey Konovalov wrote:
> Hi,
> 
> I'm getting a crash when trying to load a module into a kernel that
> uses __ro_after_init static labels, see the crash below. The label is
> defined and initialized in the main kernel binary, and is used in the
> module. Is this not supported?

Clearly not, but also, the whole RO thing never went past the
maintainers (it also seems to be missing a MAINTAINERs entry).

>  static_key_set_linked kernel/jump_label.c:368
>  jump_label_add_module+0x1ec/0x2dc kernel/jump_label.c:658
>  jump_label_module_notify+0x40/0xa4 kernel/jump_label.c:736

This, it needs to modify the key, which is RO, to add a list of sites
from the module.

It could probably be fixed..