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

[Dylan Hatch]

On Mon, Apr 21, 2025 at 11:25 PM Song Liu <song at kernel.org> wrote:
>
> On Mon, Apr 21, 2025 at 5:35 PM Song Liu <song at kernel.org> wrote:
> >
> > On Fri, Apr 11, 2025 at 6:10 PM Dylan Hatch <dylanbhatch at google.com> 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 at google.com>
>
> Could you please share how you test this?
>

For context, we enable livepatch for arm64 by porting this RFC series
(along with other internal patches) into our kernel:
https://lore.kernel.org/all/20230202074036.507249-1-madvenka@linux.microsoft.com/.

The way I tested this patch is: with STRICT_MODULE_RWX, load a module
and a livepatch that touches that module (in either order), and
confirm the kernel doesn't crash.

Without this patch, a crash is caused in apply_relocate_add() if both
a module and a livepatch that touches the module are both loaded. This
happens through one of two code paths:

  1. If the module is already loaded when the livepatch is applied,
through the module_init() callback.
  2. If the module is loaded after the livepatch is applied, through
prepare_coming_module().

In both scenarios, the livepatch module's text is already RX-only.

Thanks,
Dylan