linux-kernel - Re: [RFC PATCH 3/3] kallsyms: add option to include relative filepaths into kallsyms

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Message-Id: <20220819105001.1130876-1-alexandr.lobakin@intel.com>
Date:   Fri, 19 Aug 2022 12:50:01 +0200
From:   Alexander Lobakin <alexandr.lobakin@...el.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Alexander Lobakin <alexandr.lobakin@...el.com>,
        linux-kernel@...r.kernel.org,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Petr Mladek <pmladek@...e.com>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        linux-kbuild@...r.kernel.org, live-patching@...r.kernel.org,
        lkp@...el.com, stable@...r.kernel.org
Subject: Re: [RFC PATCH 3/3] kallsyms: add option to include relative filepaths into kallsyms

From: Greg KH <gregkh@...uxfoundation.org>
Date: Thu, 18 Aug 2022 16:11:10 +0200

> On Thu, Aug 18, 2022 at 03:56:29PM +0200, Alexander Lobakin wrote:
> > From: Greg KH <gregkh@...uxfoundation.org>
> > Date: Thu, 18 Aug 2022 14:23:43 +0200
> > 
> > > On Thu, Aug 18, 2022 at 01:53:06PM +0200, Alexander Lobakin wrote:
> > > > Currently, kallsyms kernel code copes with symbols with the same
> > > > name by indexing them according to their position in vmlinux and
> > > > requiring to provide an index of the desired symbol. This is not
> > > > really quite reliable and is fragile to any features performing
> > > > symbol or section manipulations such as FG-KASLR.
> > > 
> > > Ah, here's the reasoning, stuff like this should go into the 0/X message
> > > too, right?
> > > 
> > > Anyway, what is currently broken that requires this?  What will this
> > > make easier in the future?  What in the future will depend on this?
> > 
> > 2) FG-KASLR will depend and probably some more crazy hardening
> >    stuff. And/or perf-based function/symbol placement, which is
> >    in the "discuss and dream sometimes" stage.
> 
> I have no idea what "FG-KASLR" is.  Why not submit these changes when
> whatever that is is ready for submission?

It doesn't matter much, the main idea is that the current approach
with relying on symbol positions in the vmlinux is broken when we
reorder symbols during the kernel initialization.
As I said, this is an early RFC do discuss the idea and the
implementation. I could submit it along with FG-KASLR, but then if
there would be major change requests, I'd need to redo lots of
stuff, which is not very efficient. It's better to settle down the
implementation details in advance.
Plus this kallsyms feature goes standalone as it gets bigger. It
will contain a pack of commits and touch several different
subsystems. Mixing all of this with FG-KASLR in one series doesn't
sound good to me.

> 
> thanks,
> 
> greg k-h

Thanks,
Olek