2023-07-01 17:40:45

by SeongJae Park

Subject: [PATCH v3] btf: warn but return no error for NULL btf from __register_btf_kfunc_id_set()

__register_btf_kfunc_id_set() assumes .BTF to be part of the module's
.ko file if CONFIG_DEBUG_INFO_BTF is enabled. If that's not the case,
the function prints an error message and return an error. As a result,
such modules cannot be loaded.

However, the section could be stripped out during a build process. It
would be better to let the modules loaded, because their basic
functionalities have no problem[1], though the BTF functionalities will
not be supported. Make the function to lower the level of the message
from error to warn, and return no error.

[1] https://lore.kernel.org/bpf/[email protected]/

Reported-by: Alexander Egorenkov <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]/
Suggested-by: Kumar Kartikeya Dwivedi <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]/
Fixes: c446fdacb10d ("bpf: fix register_btf_kfunc_id_set for !CONFIG_DEBUG_INFO_BTF")
Cc: <[email protected]> # 5.18.x
Signed-off-by: SeongJae Park <[email protected]>
Acked-by: Jiri Olsa <[email protected]>
Signed-off-by: SeongJae Park <[email protected]>
---

Changes from v2
(https://lore.kernel.org/bpf/[email protected]/)
- Keep the error for vmlinux case.
Changes from v1
(https://lore.kernel.org/all/[email protected]/)
- Fix Fixes: tag (Jiri Olsa)
- Add 'Acked-by: ' from Jiri Olsa

Notes
- This is a fix. Hence, would better to merged into bpf tree, not
bpf-next.
- This doesn't cleanly applied on 6.1.y. I will send the backport to
stable@ as soon as this is merged into the mainline.

kernel/bpf/btf.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 29fe21099298..817204d53372 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -7891,10 +7891,8 @@ static int __register_btf_kfunc_id_set(enum btf_kfunc_hook hook,
pr_err("missing vmlinux BTF, cannot register kfuncs\n");
return -ENOENT;
}
- if (kset->owner && IS_ENABLED(CONFIG_DEBUG_INFO_BTF_MODULES)) {
- pr_err("missing module BTF, cannot register kfuncs\n");
- return -ENOENT;
- }
+ if (kset->owner && IS_ENABLED(CONFIG_DEBUG_INFO_BTF_MODULES))
+ pr_warn("missing module BTF, cannot register kfuncs\n");
return 0;
}
if (IS_ERR(btf))
--
2.25.1

2023-07-03 17:03:07

by Daniel Borkmann

Subject: Re: [PATCH v3] btf: warn but return no error for NULL btf from __register_btf_kfunc_id_set()

On 7/1/23 7:14 PM, SeongJae Park wrote:
> __register_btf_kfunc_id_set() assumes .BTF to be part of the module's
> .ko file if CONFIG_DEBUG_INFO_BTF is enabled. If that's not the case,
> the function prints an error message and return an error. As a result,
> such modules cannot be loaded.
>
> However, the section could be stripped out during a build process. It
> would be better to let the modules loaded, because their basic
> functionalities have no problem[1], though the BTF functionalities will
> not be supported. Make the function to lower the level of the message
> from error to warn, and return no error.
>
> [1] https://lore.kernel.org/bpf/[email protected]/
>
> Reported-by: Alexander Egorenkov <[email protected]>
> Link: https://lore.kernel.org/bpf/[email protected]/
> Suggested-by: Kumar Kartikeya Dwivedi <[email protected]>
> Link: https://lore.kernel.org/bpf/[email protected]/
> Fixes: c446fdacb10d ("bpf: fix register_btf_kfunc_id_set for !CONFIG_DEBUG_INFO_BTF")
> Cc: <[email protected]> # 5.18.x
> Signed-off-by: SeongJae Park <[email protected]>
> Acked-by: Jiri Olsa <[email protected]>
> Signed-off-by: SeongJae Park <[email protected]>
> ---
>
> Changes from v2
> (https://lore.kernel.org/bpf/[email protected]/)
> - Keep the error for vmlinux case.

Looks good, applied to bpf, thanks!