linux-kernel - Re: [PATCH v3 5/6] x86/ftrace: Use text

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Date:   Wed, 16 Oct 2019 09:49:51 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Joe Lawrence <joe.lawrence@...hat.com>,
        Jessica Yu <jeyu@...nel.org>, Miroslav Benes <mbenes@...e.cz>,
        x86@...nel.org, linux-kernel@...r.kernel.org, mhiramat@...nel.org,
        bristot@...hat.com, jbaron@...mai.com,
        torvalds@...ux-foundation.org, tglx@...utronix.de,
        mingo@...nel.org, namit@...are.com, hpa@...or.com, luto@...nel.org,
        ard.biesheuvel@...aro.org, jpoimboe@...hat.com,
        live-patching@...r.kernel.org
Subject: Re: [PATCH v3 5/6] x86/ftrace: Use text_poke()

On Tue, Oct 15, 2019 at 06:27:05PM -0400, Steven Rostedt wrote:

> (7) Seventh session, titled "klp-convert and livepatch relocations", was led
> by Joe Lawrence.
> 
> Joe started the session with problem statement: accessing non exported / static
> symbols from inside the patch module. One possible workardound is manually via
> kallsyms. Second workaround is klp-convert, which actually creates proper
> relocations inside the livepatch module from the symbol database during the
> final .ko link.
> Currently module loader looks for special livepatch relocations and resolves
> those during runtime; kernel support for these relocations have so far been
> added for x86 only. Special livepatch relocations are supported and processed
> also on other architectures. Special quirks/sections are not yet supported.
> Plus klp-convert would still be needed even with late module patching update.
> vmlinux or modules could have ambiguous static symbols.
> 
> It turns out that the features / bugs below have to be resolved before we
> can claim the klp-convert support for relocation complete:
>     - handle all the corner cases (jump labels, static keys, ...) properly and
>       have a good regression tests in place

I suppose all the patches in this series-of-series here will make life
harder for KLP, static_call() and 2 byte jumps etc..

>     - one day we might (or might not) add support for out-of-tree modules which
>       need klp-convert
>     - BFD bug 24456 (multiple relocations to the same .text section)