linux-hardening - Re: [PATCH v9 02/15] livepatch: use `-z unique-symbol` if available to nuke pos-based search

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Date:   Mon, 3 Jan 2022 14:55:42 +0100 (CET)
From:   Miroslav Benes <mbenes@...e.cz>
To:     Fāng-ruì Sòng <maskray@...gle.com>
cc:     Alexander Lobakin <alexandr.lobakin@...el.com>,
        Borislav Petkov <bp@...en8.de>,
        linux-hardening@...r.kernel.org, x86@...nel.org,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Kristen Carlson Accardi <kristen@...ux.intel.com>,
        Kees Cook <keescook@...omium.org>,
        Miklos Szeredi <miklos@...redi.hu>,
        Ard Biesheuvel <ardb@...nel.org>,
        Tony Luck <tony.luck@...el.com>,
        Bruce Schlobohm <bruce.schlobohm@...el.com>,
        Jessica Yu <jeyu@...nel.org>,
        kernel test robot <lkp@...el.com>,
        Evgenii Shatokhin <eshatokhin@...tuozzo.com>,
        Jonathan Corbet <corbet@....net>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will@...nel.org>, Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Arnd Bergmann <arnd@...db.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
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        Marios Pomonis <pomonis@...gle.com>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        "H.J. Lu" <hjl.tools@...il.com>, Nicolas Pitre <nico@...xnic.net>,
        linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org,
        linux-arch@...r.kernel.org, live-patching@...r.kernel.org,
        llvm@...ts.linux.dev
Subject: Re: [PATCH v9 02/15] livepatch: use `-z unique-symbol` if available
 to nuke pos-based search

On Thu, 30 Dec 2021, Fāng-ruì Sòng wrote:

> On Thu, Dec 30, 2021 at 3:11 AM Borislav Petkov <bp@...en8.de> wrote:
> >
> > On Thu, Dec 23, 2021 at 01:21:56AM +0100, Alexander Lobakin wrote:
> > > [PATCH v9 02/15] livepatch: use `-z unique-symbol` if available to nuke pos-based search

...

> Apologies since I haven't read the patch series.
> 
> The option does not exist in ld.lld and I am a bit concerning about
> its semantics: https://maskray.me/blog/2020-11-15-explain-gnu-linker-options#z-unique-symbol
> 
> I thought that someone forwarded my comments (originally posted months
> on a feature request ago) here but seems not.
> (I am a ld.lld maintainer.)

Do you mean 
https://lore.kernel.org/all/20210123225928.z5hkmaw6qjs2gu5g@google.com/T/#u 
?

Unfortunately, it did not lead anywhere. I think that '-z unique-symbol' 
option should work fine as long as the live patching is concerned. Maybe I 
misunderstood but your concerns mentioned at the blog do not apply. The 
stability is not an issue for us since we (KLP) always work with already 
built and fixed kernel. And(at least) GCC already uses number suffices for 
IPA clones and it has not been a problem anywhere.

Am I wrong?

Thanks

Miroslav