[GIT PULL] Modules updates for v5.13

[GIT PULL] Modules updates for v5.13

[Jessica Yu]

Hi Linus,

Please pull below to receive modules updates for the v5.13 merge window.
A summary can be found in the signed tag.

Thank you,

Jessica

--
The following changes since commit 1e28eed17697bcf343c6743f0028cc3b5dd88bf0:

   Linux 5.12-rc3 (2021-03-14 14:41:02 -0700)

are available in the Git repository at:

   git://git.kernel.org/pub/scm/linux/kernel/git/jeyu/linux.git tags/modules-for-v5.13

for you to fetch changes up to 33121347fb1c359bd6e3e680b9f2c6ced5734a81:

   module: treat exit sections the same as init sections when !CONFIG_MODULE_UNLOAD (2021-03-29 13:08:53 +0200)

----------------------------------------------------------------
Modules updates for v5.13

Summary of modules changes for the 5.13 merge window:

- Fix an age old bug involving jump_calls and static_labels when
   CONFIG_MODULE_UNLOAD=n. When CONFIG_MODULE_UNLOAD=n, it means you
   can't unload modules, so normally the __exit sections of a module are
   not loaded at all. However, dynamic code patching (jump_label,
   static_call, alternatives) can have sites in __exit sections even if
   __exit is never executed.

   Reported by Peter Zijlstra: "Alternatives, jump_labels and static_call
   all can have relocations into __exit code.  Not loading it at all would
   be BAD." Therefore, load the __exit sections even when
   CONFIG_MODULE_UNLOAD=n, and discard them after init.

Signed-off-by: Jessica Yu <jeyu@kernel.org>

----------------------------------------------------------------
Jessica Yu (1):
       module: treat exit sections the same as init sections when !CONFIG_MODULE_UNLOAD

  kernel/module.c | 9 ++++-----
  1 file changed, 4 insertions(+), 5 deletions(-)

Re: [GIT PULL] Modules updates for v5.13

[Jessica Yu]

+++ Jessica Yu [28/04/21 14:58 +0200]:
>Hi Linus,
>
>Please pull below to receive modules updates for the v5.13 merge window.
>A summary can be found in the signed tag.
>
>Thank you,
>
>Jessica

Ugh, I had forgotten to sign the tag. Should be fixed now, sorry about that.

>--
>The following changes since commit 1e28eed17697bcf343c6743f0028cc3b5dd88bf0:
>
>  Linux 5.12-rc3 (2021-03-14 14:41:02 -0700)
>
>are available in the Git repository at:
>
>  git://git.kernel.org/pub/scm/linux/kernel/git/jeyu/linux.git tags/modules-for-v5.13
>
>for you to fetch changes up to 33121347fb1c359bd6e3e680b9f2c6ced5734a81:
>
>  module: treat exit sections the same as init sections when !CONFIG_MODULE_UNLOAD (2021-03-29 13:08:53 +0200)
>
>----------------------------------------------------------------
>Modules updates for v5.13
>
>Summary of modules changes for the 5.13 merge window:
>
>- Fix an age old bug involving jump_calls and static_labels when
>  CONFIG_MODULE_UNLOAD=n. When CONFIG_MODULE_UNLOAD=n, it means you
>  can't unload modules, so normally the __exit sections of a module are
>  not loaded at all. However, dynamic code patching (jump_label,
>  static_call, alternatives) can have sites in __exit sections even if
>  __exit is never executed.
>
>  Reported by Peter Zijlstra: "Alternatives, jump_labels and static_call
>  all can have relocations into __exit code.  Not loading it at all would
>  be BAD." Therefore, load the __exit sections even when
>  CONFIG_MODULE_UNLOAD=n, and discard them after init.
>
>Signed-off-by: Jessica Yu <jeyu@kernel.org>
>
>----------------------------------------------------------------
>Jessica Yu (1):
>      module: treat exit sections the same as init sections when !CONFIG_MODULE_UNLOAD
>
> kernel/module.c | 9 ++++-----
> 1 file changed, 4 insertions(+), 5 deletions(-)

Re: [GIT PULL] Modules updates for v5.13

[Linus Torvalds]

On Wed, Apr 28, 2021 at 5:58 AM Jessica Yu <jeyu@kernel.org> wrote:
>
>    Therefore, load the __exit sections even when
>    CONFIG_MODULE_UNLOAD=n, and discard them after init.

So I've pulled this, but I have two questions based on reading the patch..

 (a) Where's that "discard them after init" logic?

 (b) ARM has its own module_init/exit_section() functions, and now
seems to have different logic than everybody else as a result..

but maybe I'm not reading that patch right.

               Linus

Re: [GIT PULL] Modules updates for v5.13

[Jessica Yu]

+++ Linus Torvalds [30/04/21 12:37 -0700]:
>On Wed, Apr 28, 2021 at 5:58 AM Jessica Yu <jeyu@kernel.org> wrote:
>>
>>    Therefore, load the __exit sections even when
>>    CONFIG_MODULE_UNLOAD=n, and discard them after init.

Hi Linus,

>So I've pulled this, but I have two questions based on reading the patch..
>
> (a) Where's that "discard them after init" logic?

So the idea is for the exit sections to additionally identify as init
sections via module_init_section() when CONFIG_MODULE_UNLOAD=n, so
that the existing logic in layout_sections() picks this up and puts
the exit sections into the init area of the module (mod->init_layout.base).

Then, since we've placed the exit sections in the init region of the
module, they will automatically get freed at the end of
do_init_module() with the rest of the init sections. Peter has also
mentioned that jump_label and static_call want the exit sections to
also identify as init via within_module_init(), so this change should
satisfy their requirement as well. I should have explained this more
in the changelog and apologize that it wasn't clear.

> (b) ARM has its own module_init/exit_section() functions, and now
>seems to have different logic than everybody else as a result..

No, you are right, I had forgotten that ARM is a special case :-( I
will add a similar hunk for ARM and submit that for the next -rc so
that all arches are on the same page here.


Jessica

Re: [GIT PULL] Modules updates for v5.13

[pr-tracker-bot]

The pull request you sent on Wed, 28 Apr 2021 14:58:44 +0200:

> git://git.kernel.org/pub/scm/linux/kernel/git/jeyu/linux.git tags/modules-for-v5.13

has been merged into torvalds/linux.git:
https://git.kernel.org/torvalds/c/65c61de9d090edb8a3cfb3f45541e268eb2cdb13

Thank you!

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