linux-kernel - Re: [PATCH v2 2/2] arm64/module: Use text-poke API for late relocations.

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Message-ID: <CAPhsuW4rgcw3Dqam4Hethrkd0jqzuwebh365g-7xkg_g1QM78Q@mail.gmail.com>
Date: Fri, 9 May 2025 09:39:26 -0700
From: Song Liu <song@...nel.org>
To: Will Deacon <will@...nel.org>
Cc: Dylan Hatch <dylanbhatch@...gle.com>, Daniel Borkmann <daniel@...earbox.net>, 
	Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, 
	Eduard Zingerman <eddyz87@...il.com>, Yonghong Song <yonghong.song@...ux.dev>, 
	John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>, 
	Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>, 
	Puranjay Mohan <puranjay@...nel.org>, Xu Kuohai <xukuohai@...weicloud.com>, 
	Philippe Mathieu-Daudé <philmd@...aro.org>, 
	Catalin Marinas <catalin.marinas@....com>, "Mike Rapoport (Microsoft)" <rppt@...nel.org>, Arnd Bergmann <arnd@...db.de>, 
	Geert Uytterhoeven <geert@...ux-m68k.org>, Luis Chamberlain <mcgrof@...nel.org>, 
	Andrew Morton <akpm@...ux-foundation.org>, Ard Biesheuvel <ardb@...nel.org>, 
	Mark Rutland <mark.rutland@....com>, linux-arm-kernel@...ts.infradead.org, 
	linux-kernel@...r.kernel.org, Roman Gushchin <roman.gushchin@...ux.dev>
Subject: Re: [PATCH v2 2/2] arm64/module: Use text-poke API for late relocations.

Hi Will,

On Fri, May 9, 2025 at 9:15 AM Will Deacon <will@...nel.org> wrote:
>
> Hi Dylan,
>
> On Sat, Apr 12, 2025 at 01:09:39AM +0000, Dylan Hatch wrote:
> > To enable late module patching, livepatch modules need to be able to
> > apply some of their relocations well after being loaded. In this
> > scenario, use the text-poking API to allow this, even with
> > STRICT_MODULE_RWX.
> >
> > This patch is largely based off commit 88fc078a7a8f6 ("x86/module: Use
> > text_poke() for late relocations").
> >
> > Signed-off-by: Dylan Hatch <dylanbhatch@...gle.com>
> > ---
> >  arch/arm64/kernel/module.c | 129 ++++++++++++++++++++++++-------------
> >  1 file changed, 83 insertions(+), 46 deletions(-)
>
> On its own, this isn't gaining us an awful lot upstream as we don't have
> livepatch support (arm64 does not select HAVE_LIVEPATCH), however I'm
> not against incremental changes towards enabling that. Are you planning
> to work on follow-up changes for the rest of the support?

There are two patchsets that are trying to enable HAVE_LIVEPATCH
for arm64:

[1] https://lore.kernel.org/all/20250127213310.2496133-1-wnliu@google.com/
[2] https://lore.kernel.org/linux-arm-kernel/20250320171559.3423224-1-song@kernel.org/

Toshiyuki has tested this patch with both approaches.

Since patchset [1] depends on SFrame, which is less mature at the
moment (clang doesn't support it, kernel side code is very new), live patch
folks think [2] is a better approach at the moment. Could you please share
your thoughts on [2]. If it looks good, we hope to ship it to 6.16 kernels, as
we (Meta) want to use livepatch in our fleet.

Thanks,
Song