linux-kernel - Re: [PATCH v2] arm64/module: use plt section indices for relocations

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Message-ID: <alpine.LSU.2.21.1811061043270.23386@pobox.suse.cz>
Date:   Tue, 6 Nov 2018 10:44:27 +0100 (CET)
From:   Miroslav Benes <mbenes@...e.cz>
To:     Will Deacon <will.deacon@....com>
cc:     Jessica Yu <jeyu@...nel.org>, Torsten Duwe <duwe@....de>,
        Catalin Marinas <catalin.marinas@....com>,
        Julien Thierry <julien.thierry@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        AKASHI Takahiro <takahiro.akashi@...aro.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        live-patching@...r.kernel.org
Subject: Re: [PATCH v2] arm64/module: use plt section indices for
 relocations

On Mon, 5 Nov 2018, Will Deacon wrote:

> On Mon, Nov 05, 2018 at 07:53:23PM +0100, Jessica Yu wrote:
> > Instead of saving a pointer to the .plt and .init.plt sections to apply
> > plt-based relocations, save and use their section indices instead.
> > 
> > The mod->arch.{core,init}.plt pointers were problematic for livepatch
> > because they pointed within temporary section headers (provided by the
> > module loader via info->sechdrs) that would be freed after module load.
> > Since livepatch modules may need to apply relocations post-module-load
> > (for example, to patch a module that is loaded later), using section
> > indices to offset into the section headers (instead of accessing them
> > through a saved pointer) allows livepatch modules on arm64 to pass in
> > their own copy of the section headers to apply_relocate_add() to apply
> > delayed relocations.
> > 
> > Signed-off-by: Jessica Yu <jeyu@...nel.org>
> > ---
> > 
> > v2:
> > 
> > - Do sechdrs[pltsec->plt_shndx].sh_addr instead of pointer math
> > 
> > Note: Addressed Will's comment about the pltsec -> plt_info rename and
> > removed that change to reduce unnecessary code churn. I didn't include the
> > Ack's for this reason so let me know if this version is OK as well.
> 
> Thanks, Jessica!
> 
> Acked-by: Will Deacon <will.deacon@....com>
> 
> > arch/arm64/include/asm/module.h |  8 +++++---
> > arch/arm64/kernel/module-plts.c | 36 ++++++++++++++++++++----------------
> > arch/arm64/kernel/module.c      |  9 +++++----
> > 3 files changed, 30 insertions(+), 23 deletions(-)
> 
> Actually, I guess I should just queue this for 4.21 given that it's
> completely self-contained.

FWIW you can also add my

Reviewed-by: Miroslav Benes <mbenes@...e.cz>

Thanks, Jessica.

Miroslav