[PATCH net-next] bpf: add helper capable of reading out instructions

[PATCH net-next] bpf: add helper capable of reading out instructions

[Jakub Kicinski]

To read translated and jited instructions from the kernel,
one has to set certain pointers of struct bpf_prog_info to
pre-allocated user buffers.  Unfortunately, the existing
bpf_obj_get_info_by_fd() helper zeros struct bpf_prog_info
before passing it to the kernel.

Keeping the zeroing seems like a good idea in general, since
kernel will check if the structure was zeroed.  Add a new
helper for those more advanced users who can be trusted to
take care of zeroing themselves.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
---
I'm happy to change the name of the new function.

 tools/lib/bpf/bpf.c | 10 ++++++++--
 tools/lib/bpf/bpf.h |  2 ++
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index 412a7c82995a..2703fa282b65 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -308,13 +308,12 @@ int bpf_map_get_fd_by_id(__u32 id)
 	return sys_bpf(BPF_MAP_GET_FD_BY_ID, &attr, sizeof(attr));
 }
 
-int bpf_obj_get_info_by_fd(int prog_fd, void *info, __u32 *info_len)
+int __bpf_obj_get_info_by_fd(int prog_fd, void *info, __u32 *info_len)
 {
 	union bpf_attr attr;
 	int err;
 
 	bzero(&attr, sizeof(attr));
-	bzero(info, *info_len);
 	attr.info.bpf_fd = prog_fd;
 	attr.info.info_len = *info_len;
 	attr.info.info = ptr_to_u64(info);
@@ -325,3 +324,10 @@ int bpf_obj_get_info_by_fd(int prog_fd, void *info, __u32 *info_len)
 
 	return err;
 }
+
+int bpf_obj_get_info_by_fd(int prog_fd, void *info, __u32 *info_len)
+{
+	bzero(info, *info_len);
+
+	return __bpf_obj_get_info_by_fd(prog_fd, info, info_len);
+}
diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
index 418c86e69bcb..e44b423ac07e 100644
--- a/tools/lib/bpf/bpf.h
+++ b/tools/lib/bpf/bpf.h
@@ -58,6 +58,8 @@ int bpf_prog_get_next_id(__u32 start_id, __u32 *next_id);
 int bpf_map_get_next_id(__u32 start_id, __u32 *next_id);
 int bpf_prog_get_fd_by_id(__u32 id);
 int bpf_map_get_fd_by_id(__u32 id);
+/* Note: bpf_obj_get_info_by_fd() will init info to zeroes */
 int bpf_obj_get_info_by_fd(int prog_fd, void *info, __u32 *info_len);
+int __bpf_obj_get_info_by_fd(int prog_fd, void *info, __u32 *info_len);
 
 #endif
-- 
2.11.0

Re: [PATCH net-next] bpf: add helper capable of reading out instructions

[Daniel Borkmann]

[ +Martin ]

On 07/24/2017 11:22 PM, Jakub Kicinski wrote:
> To read translated and jited instructions from the kernel,
> one has to set certain pointers of struct bpf_prog_info to
> pre-allocated user buffers.  Unfortunately, the existing
> bpf_obj_get_info_by_fd() helper zeros struct bpf_prog_info
> before passing it to the kernel.
>
> Keeping the zeroing seems like a good idea in general, since
> kernel will check if the structure was zeroed.  Add a new
> helper for those more advanced users who can be trusted to
> take care of zeroing themselves.
>
> Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
> ---
> I'm happy to change the name of the new function.
>
>   tools/lib/bpf/bpf.c | 10 ++++++++--
>   tools/lib/bpf/bpf.h |  2 ++
>   2 files changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
> index 412a7c82995a..2703fa282b65 100644
> --- a/tools/lib/bpf/bpf.c
> +++ b/tools/lib/bpf/bpf.c
> @@ -308,13 +308,12 @@ int bpf_map_get_fd_by_id(__u32 id)
>   	return sys_bpf(BPF_MAP_GET_FD_BY_ID, &attr, sizeof(attr));
>   }
>
> -int bpf_obj_get_info_by_fd(int prog_fd, void *info, __u32 *info_len)
> +int __bpf_obj_get_info_by_fd(int prog_fd, void *info, __u32 *info_len)
>   {
>   	union bpf_attr attr;
>   	int err;
>
>   	bzero(&attr, sizeof(attr));
> -	bzero(info, *info_len);

Looks a bit unintentional to me, e.g. 95b9afd3987f ("bpf: Test for bpf
ID") did set up pointers in test_bpf_obj_id(), but later only checked
for the {jited,xlated}_prog_len.

Clearing out the pointers looks not to useful. Lets just push the need
for bzero() to call-sites in general in this case.

>   	attr.info.bpf_fd = prog_fd;
>   	attr.info.info_len = *info_len;
>   	attr.info.info = ptr_to_u64(info);
> @@ -325,3 +324,10 @@ int bpf_obj_get_info_by_fd(int prog_fd, void *info, __u32 *info_len)
>
>   	return err;
>   }
> +
> +int bpf_obj_get_info_by_fd(int prog_fd, void *info, __u32 *info_len)
> +{
> +	bzero(info, *info_len);
> +
> +	return __bpf_obj_get_info_by_fd(prog_fd, info, info_len);
> +}
> diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
> index 418c86e69bcb..e44b423ac07e 100644
> --- a/tools/lib/bpf/bpf.h
> +++ b/tools/lib/bpf/bpf.h
> @@ -58,6 +58,8 @@ int bpf_prog_get_next_id(__u32 start_id, __u32 *next_id);
>   int bpf_map_get_next_id(__u32 start_id, __u32 *next_id);
>   int bpf_prog_get_fd_by_id(__u32 id);
>   int bpf_map_get_fd_by_id(__u32 id);
> +/* Note: bpf_obj_get_info_by_fd() will init info to zeroes */
>   int bpf_obj_get_info_by_fd(int prog_fd, void *info, __u32 *info_len);
> +int __bpf_obj_get_info_by_fd(int prog_fd, void *info, __u32 *info_len);
>
>   #endif
>

Re: [PATCH net-next] bpf: add helper capable of reading out instructions

[Jakub Kicinski]

On Tue, 25 Jul 2017 18:40:23 +0200, Daniel Borkmann wrote:
> [ +Martin ]

Sorry, I thought I CCed Martin.

> On 07/24/2017 11:22 PM, Jakub Kicinski wrote:
> > To read translated and jited instructions from the kernel,
> > one has to set certain pointers of struct bpf_prog_info to
> > pre-allocated user buffers.  Unfortunately, the existing
> > bpf_obj_get_info_by_fd() helper zeros struct bpf_prog_info
> > before passing it to the kernel.
> >
> > Keeping the zeroing seems like a good idea in general, since
> > kernel will check if the structure was zeroed.  Add a new
> > helper for those more advanced users who can be trusted to
> > take care of zeroing themselves.
> >
> > Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
> > ---
> > I'm happy to change the name of the new function.
> >
> >   tools/lib/bpf/bpf.c | 10 ++++++++--
> >   tools/lib/bpf/bpf.h |  2 ++
> >   2 files changed, 10 insertions(+), 2 deletions(-)
> >
> > diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
> > index 412a7c82995a..2703fa282b65 100644
> > --- a/tools/lib/bpf/bpf.c
> > +++ b/tools/lib/bpf/bpf.c
> > @@ -308,13 +308,12 @@ int bpf_map_get_fd_by_id(__u32 id)
> >   	return sys_bpf(BPF_MAP_GET_FD_BY_ID, &attr, sizeof(attr));
> >   }
> >
> > -int bpf_obj_get_info_by_fd(int prog_fd, void *info, __u32 *info_len)
> > +int __bpf_obj_get_info_by_fd(int prog_fd, void *info, __u32 *info_len)
> >   {
> >   	union bpf_attr attr;
> >   	int err;
> >
> >   	bzero(&attr, sizeof(attr));
> > -	bzero(info, *info_len);  
> 
> Looks a bit unintentional to me, e.g. 95b9afd3987f ("bpf: Test for bpf
> ID") did set up pointers in test_bpf_obj_id(), but later only checked
> for the {jited,xlated}_prog_len.
> 
> Clearing out the pointers looks not to useful. Lets just push the need
> for bzero() to call-sites in general in this case.

Should I target this at net then?  To avoid backwards compatibility
issues?

Re: [PATCH net-next] bpf: add helper capable of reading out instructions

[Daniel Borkmann]

On 07/25/2017 08:20 PM, Jakub Kicinski wrote:
> On Tue, 25 Jul 2017 18:40:23 +0200, Daniel Borkmann wrote:
>> [ +Martin ]
>
> Sorry, I thought I CCed Martin.
>
>> On 07/24/2017 11:22 PM, Jakub Kicinski wrote:
>>> To read translated and jited instructions from the kernel,
>>> one has to set certain pointers of struct bpf_prog_info to
>>> pre-allocated user buffers.  Unfortunately, the existing
>>> bpf_obj_get_info_by_fd() helper zeros struct bpf_prog_info
>>> before passing it to the kernel.
>>>
>>> Keeping the zeroing seems like a good idea in general, since
>>> kernel will check if the structure was zeroed.  Add a new
>>> helper for those more advanced users who can be trusted to
>>> take care of zeroing themselves.
>>>
>>> Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
>>> ---
>>> I'm happy to change the name of the new function.
>>>
>>>    tools/lib/bpf/bpf.c | 10 ++++++++--
>>>    tools/lib/bpf/bpf.h |  2 ++
>>>    2 files changed, 10 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
>>> index 412a7c82995a..2703fa282b65 100644
>>> --- a/tools/lib/bpf/bpf.c
>>> +++ b/tools/lib/bpf/bpf.c
>>> @@ -308,13 +308,12 @@ int bpf_map_get_fd_by_id(__u32 id)
>>>    	return sys_bpf(BPF_MAP_GET_FD_BY_ID, &attr, sizeof(attr));
>>>    }
>>>
>>> -int bpf_obj_get_info_by_fd(int prog_fd, void *info, __u32 *info_len)
>>> +int __bpf_obj_get_info_by_fd(int prog_fd, void *info, __u32 *info_len)
>>>    {
>>>    	union bpf_attr attr;
>>>    	int err;
>>>
>>>    	bzero(&attr, sizeof(attr));
>>> -	bzero(info, *info_len);
>>
>> Looks a bit unintentional to me, e.g. 95b9afd3987f ("bpf: Test for bpf
>> ID") did set up pointers in test_bpf_obj_id(), but later only checked
>> for the {jited,xlated}_prog_len.
>>
>> Clearing out the pointers looks not to useful. Lets just push the need
>> for bzero() to call-sites in general in this case.
>
> Should I target this at net then?  To avoid backwards compatibility
> issues?

Yep, sounds reasonable. Thanks!