[PATCH v2] btf: warn but return no error for NULL btf from __register_btf_kfunc_id_set()

[PATCH v2] btf: warn but return no error for NULL btf from __register_btf_kfunc_id_set()

[SeongJae Park]

__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/20220219082037.ow2kbq5brktf4f2u@apollo.legion/

Reported-by: Alexander Egorenkov <Alexander.Egorenkov@ibm.com>
Link: https://lore.kernel.org/bpf/87y228q66f.fsf@oc8242746057.ibm.com/
Suggested-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/bpf/20220219082037.ow2kbq5brktf4f2u@apollo.legion/
Fixes: c446fdacb10d ("bpf: fix register_btf_kfunc_id_set for !CONFIG_DEBUG_INFO_BTF")
Cc: <stable@vger.kernel.org> # 5.18.x
Signed-off-by: SeongJae Park <sj@kernel.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
---
Changes from v1
(https://lore.kernel.org/all/20230626181120.7086-1-sj@kernel.org/)
- Fix Fixes: tag (Jiri Olsa)
- Add 'Acked-by: ' from Jiri Olsa

 kernel/bpf/btf.c | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 6b682b8e4b50..d683f034996f 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -7848,14 +7848,10 @@ static int __register_btf_kfunc_id_set(enum btf_kfunc_hook hook,
 
 	btf = btf_get_module_btf(kset->owner);
 	if (!btf) {
-		if (!kset->owner && IS_ENABLED(CONFIG_DEBUG_INFO_BTF)) {
-			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))
+			pr_warn("missing vmlinux BTF, cannot register kfuncs\n");
+		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

Re: [PATCH v2] btf: warn but return no error for NULL btf from __register_btf_kfunc_id_set()

[Daniel Borkmann]

On 6/28/23 6:46 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/20220219082037.ow2kbq5brktf4f2u@apollo.legion/
> 
> Reported-by: Alexander Egorenkov <Alexander.Egorenkov@ibm.com>
> Link: https://lore.kernel.org/bpf/87y228q66f.fsf@oc8242746057.ibm.com/
> Suggested-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
> Link: https://lore.kernel.org/bpf/20220219082037.ow2kbq5brktf4f2u@apollo.legion/
> Fixes: c446fdacb10d ("bpf: fix register_btf_kfunc_id_set for !CONFIG_DEBUG_INFO_BTF")
> Cc: <stable@vger.kernel.org> # 5.18.x
> Signed-off-by: SeongJae Park <sj@kernel.org>
> Acked-by: Jiri Olsa <jolsa@kernel.org>

I presume this one is targeted at bpf (rather than bpf-next) tree, right?

> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index 6b682b8e4b50..d683f034996f 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -7848,14 +7848,10 @@ static int __register_btf_kfunc_id_set(enum btf_kfunc_hook hook,
>   
>   	btf = btf_get_module_btf(kset->owner);
>   	if (!btf) {
> -		if (!kset->owner && IS_ENABLED(CONFIG_DEBUG_INFO_BTF)) {
> -			pr_err("missing vmlinux BTF, cannot register kfuncs\n");
> -			return -ENOENT;
> -		}

Why the above one needs to be changed? Do you also run into this case? vmlinux BTF
should be built-in in this case. I understand it's rather the one below for BTF +
modules instead, no?

> -		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))
> +			pr_warn("missing vmlinux BTF, cannot register kfuncs\n");
> +		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))
> 

Re: [PATCH v2] btf: warn but return no error for NULL btf from __register_btf_kfunc_id_set()

[SeongJae Park]

Hi Daniel,

On Fri, 30 Jun 2023 16:53:38 +0200 Daniel Borkmann <daniel@iogearbox.net> wrote:

> On 6/28/23 6:46 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/20220219082037.ow2kbq5brktf4f2u@apollo.legion/
> > 
> > Reported-by: Alexander Egorenkov <Alexander.Egorenkov@ibm.com>
> > Link: https://lore.kernel.org/bpf/87y228q66f.fsf@oc8242746057.ibm.com/
> > Suggested-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
> > Link: https://lore.kernel.org/bpf/20220219082037.ow2kbq5brktf4f2u@apollo.legion/
> > Fixes: c446fdacb10d ("bpf: fix register_btf_kfunc_id_set for !CONFIG_DEBUG_INFO_BTF")
> > Cc: <stable@vger.kernel.org> # 5.18.x
> > Signed-off-by: SeongJae Park <sj@kernel.org>
> > Acked-by: Jiri Olsa <jolsa@kernel.org>
> 
> I presume this one is targeted at bpf (rather than bpf-next) tree, right?

You're correct.  It's not urgent for us, but I would prefer it to be merged
into all affected kernels as early as possible.

> 
> > diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> > index 6b682b8e4b50..d683f034996f 100644
> > --- a/kernel/bpf/btf.c
> > +++ b/kernel/bpf/btf.c
> > @@ -7848,14 +7848,10 @@ static int __register_btf_kfunc_id_set(enum btf_kfunc_hook hook,
> >   
> >   	btf = btf_get_module_btf(kset->owner);
> >   	if (!btf) {
> > -		if (!kset->owner && IS_ENABLED(CONFIG_DEBUG_INFO_BTF)) {
> > -			pr_err("missing vmlinux BTF, cannot register kfuncs\n");
> > -			return -ENOENT;
> > -		}
> 
> Why the above one needs to be changed? Do you also run into this case? vmlinux BTF
> should be built-in in this case. I understand it's rather the one below for BTF +
> modules instead, no?

Again, you're correct.  This change is not really needed.  I was interpreting
Kumar's suggestion merely into code without thinking about his real meaning,
sorry.  I will restore this in the next spin.


Thanks,
SJ

> 
> > -		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))
> > +			pr_warn("missing vmlinux BTF, cannot register kfuncs\n");
> > +		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))
> > 
> 
> 

Re: [PATCH v2] btf: warn but return no error for NULL btf from __register_btf_kfunc_id_set()

[Daniel Borkmann]

On 6/30/23 9:48 PM, SeongJae Park wrote:
> On Fri, 30 Jun 2023 16:53:38 +0200 Daniel Borkmann <daniel@iogearbox.net> wrote:
>> On 6/28/23 6:46 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/20220219082037.ow2kbq5brktf4f2u@apollo.legion/
>>>
>>> Reported-by: Alexander Egorenkov <Alexander.Egorenkov@ibm.com>
>>> Link: https://lore.kernel.org/bpf/87y228q66f.fsf@oc8242746057.ibm.com/
>>> Suggested-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
>>> Link: https://lore.kernel.org/bpf/20220219082037.ow2kbq5brktf4f2u@apollo.legion/
>>> Fixes: c446fdacb10d ("bpf: fix register_btf_kfunc_id_set for !CONFIG_DEBUG_INFO_BTF")
>>> Cc: <stable@vger.kernel.org> # 5.18.x
>>> Signed-off-by: SeongJae Park <sj@kernel.org>
>>> Acked-by: Jiri Olsa <jolsa@kernel.org>
>>
>> I presume this one is targeted at bpf (rather than bpf-next) tree, right?
> 
> You're correct.  It's not urgent for us, but I would prefer it to be merged
> into all affected kernels as early as possible.

Ok, sounds good, bpf tree it is then.

>>> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
>>> index 6b682b8e4b50..d683f034996f 100644
>>> --- a/kernel/bpf/btf.c
>>> +++ b/kernel/bpf/btf.c
>>> @@ -7848,14 +7848,10 @@ static int __register_btf_kfunc_id_set(enum btf_kfunc_hook hook,
>>>    
>>>    	btf = btf_get_module_btf(kset->owner);
>>>    	if (!btf) {
>>> -		if (!kset->owner && IS_ENABLED(CONFIG_DEBUG_INFO_BTF)) {
>>> -			pr_err("missing vmlinux BTF, cannot register kfuncs\n");
>>> -			return -ENOENT;
>>> -		}
>>
>> Why the above one needs to be changed? Do you also run into this case? vmlinux BTF
>> should be built-in in this case. I understand it's rather the one below for BTF +
>> modules instead, no?
> 
> Again, you're correct.  This change is not really needed.  I was interpreting
> Kumar's suggestion merely into code without thinking about his real meaning,
> sorry.  I will restore this in the next spin.

Perfect, I think after your v3 respin it should be good to land.

Thanks,
Daniel

Re: [PATCH v2] btf: warn but return no error for NULL btf from __register_btf_kfunc_id_set()

[SeongJae Park]

On Fri, 30 Jun 2023 22:52:24 +0200 Daniel Borkmann <daniel@iogearbox.net> wrote:

> On 6/30/23 9:48 PM, SeongJae Park wrote:
> > On Fri, 30 Jun 2023 16:53:38 +0200 Daniel Borkmann <daniel@iogearbox.net> wrote:
> >> On 6/28/23 6:46 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/20220219082037.ow2kbq5brktf4f2u@apollo.legion/
> >>>
> >>> Reported-by: Alexander Egorenkov <Alexander.Egorenkov@ibm.com>
> >>> Link: https://lore.kernel.org/bpf/87y228q66f.fsf@oc8242746057.ibm.com/
> >>> Suggested-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
> >>> Link: https://lore.kernel.org/bpf/20220219082037.ow2kbq5brktf4f2u@apollo.legion/
> >>> Fixes: c446fdacb10d ("bpf: fix register_btf_kfunc_id_set for !CONFIG_DEBUG_INFO_BTF")
> >>> Cc: <stable@vger.kernel.org> # 5.18.x
> >>> Signed-off-by: SeongJae Park <sj@kernel.org>
> >>> Acked-by: Jiri Olsa <jolsa@kernel.org>
> >>
> >> I presume this one is targeted at bpf (rather than bpf-next) tree, right?
> > 
> > You're correct.  It's not urgent for us, but I would prefer it to be merged
> > into all affected kernels as early as possible.
> 
> Ok, sounds good, bpf tree it is then.
> 
> >>> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> >>> index 6b682b8e4b50..d683f034996f 100644
> >>> --- a/kernel/bpf/btf.c
> >>> +++ b/kernel/bpf/btf.c
> >>> @@ -7848,14 +7848,10 @@ static int __register_btf_kfunc_id_set(enum btf_kfunc_hook hook,
> >>>    
> >>>    	btf = btf_get_module_btf(kset->owner);
> >>>    	if (!btf) {
> >>> -		if (!kset->owner && IS_ENABLED(CONFIG_DEBUG_INFO_BTF)) {
> >>> -			pr_err("missing vmlinux BTF, cannot register kfuncs\n");
> >>> -			return -ENOENT;
> >>> -		}
> >>
> >> Why the above one needs to be changed? Do you also run into this case? vmlinux BTF
> >> should be built-in in this case. I understand it's rather the one below for BTF +
> >> modules instead, no?
> > 
> > Again, you're correct.  This change is not really needed.  I was interpreting
> > Kumar's suggestion merely into code without thinking about his real meaning,
> > sorry.  I will restore this in the next spin.
> 
> Perfect, I think after your v3 respin it should be good to land.

Thank you!  I will send it by tomorrow, to give people enough time to comment.
If you don't want to wait, please let me know :)

Also, please note that this will not cleanly applicable on 6.1.y.  I will
provide the backport to stable@ as soon as this is merged into the mainline.


Thanks,
SJ

> 
> Thanks,
> Daniel
> 

Re: [PATCH v2] btf: warn but return no error for NULL btf from __register_btf_kfunc_id_set()

[Daniel Borkmann]

On 6/30/23 11:02 PM, SeongJae Park wrote:
[...]
> Also, please note that this will not cleanly applicable on 6.1.y.  I will
> provide the backport to stable@ as soon as this is merged into the mainline.

Perfect, thanks!