linux-kernel - Re: [PATCH] /proc/modules: honor kptr_restrict even without CONFIG

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Message-Id: <b1435818-2cba-4270-9933-282029f5449c@app.fastmail.com>
Date:   Sat, 27 May 2023 11:44:35 +0200
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Aleksander Mazur" <deweloper@...pl>,
        "Sergey Senozhatsky" <senozhatsky@...omium.org>
Cc:     linux-kernel@...r.kernel.org, "Jiri Olsa" <jolsa@...nel.org>
Subject: Re: [PATCH] /proc/modules: honor kptr_restrict even without CONFIG_KALLSYMS

On Sat, May 27, 2023, at 00:55, Aleksander Mazur wrote:
> Have you had a chance to review my patch?

I don't seem to have the original submission from you.

> Dnia 2022-06-05, o godz. 22:43:47
> Aleksander Mazur <deweloper@...pl> napisał(a):
>
>> Commit e4a8ca3baa55 fixed building without CONFIG_KALLSYMS by providing
>> dummy kallsyms_show_value(). Unfortunately -- due to hard-coded "false"
>> being returned -- access to addresses in /proc/modules became permanently
>> disabled.
>> 
>> My proposal is to change this unconditional "false" to !kptr_restrict.
>> This re-enables addresses in /proc/modules even without CONFIG_KALLSYSMS
>> unless restricted by means of sysctl (kernel.kptr_restrict).

I just looked at the original 516fb7f2e73dc ("/proc/module: use the
same logic as /proc/kallsyms for address exposure") commit again,
the intention here was to use the same logic for /proc/modules
and /proc/kallsyms.

I agree that this means my patch went too far, but I'm not sure
about yours either. Maybe we can just move kallsyms_show_value()
into a different location that is always built and rename it
accordingly. Then it can be used by both kallsyms and /proc/modules
regardless of which combination of these two is enabled in the
kernel.

     Arnd