linux-kernel - Re: [PATCH 0/3] Unexport kallsyms_lookup_name() and kallsyms_on_each

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Message-ID: <20200221162555.GA81612@google.com>
Date:   Fri, 21 Feb 2020 16:25:55 +0000
From:   Quentin Perret <qperret@...gle.com>
To:     David Laight <David.Laight@...LAB.COM>
Cc:     'Will Deacon' <will@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kernel-team@...roid.com" <kernel-team@...roid.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "K . Prasad" <prasad@...ux.vnet.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Christoph Hellwig <hch@....de>,
        Alexei Starovoitov <ast@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: [PATCH 0/3] Unexport kallsyms_lookup_name() and
 kallsyms_on_each_symbol()

On Friday 21 Feb 2020 at 15:41:35 (+0000), David Laight wrote:
> From: Will Deacon
> > Sent: 21 February 2020 11:44
> > Hi folks,
> > 
> > Despite having just a single modular in-tree user that I could spot,
> > kallsyms_lookup_name() is exported to modules and provides a mechanism
> > for out-of-tree modules to access and invoke arbitrary, non-exported
> > kernel symbols when kallsyms is enabled.
> 
> Now where did I put that kernel code that opens /proc/kallsyms and
> then reads it to find the addresses of symbols ...

Sure, but the point of this patch IIUC is not to make it totally
impossible to find the address of symbols in the kernel. It is just to
not make it utterly trivial for out-of-tree modules to bypass entirely
the upstream infrastructure for exported symbols.

All in all, I really don't see what is the benefit of keeping
kallsyms_lookup_name exported upstream. Especially since we don't have a
good use-case for it.

So, for the whole series:

  Reviewed-by: Quentin Perret <qperret@...gle.com>

Thanks,
Quentin