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

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Message-ID: <20181105192637.GB25023@brain-police>
Date:   Mon, 5 Nov 2018 19:26:38 +0000
From:   Will Deacon <will.deacon@....com>
To:     Jessica Yu <jeyu@...nel.org>
Cc:     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, 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.

Will