[bpf-next,v2,1/2] bpf: Add bpf_ktime_get_real_ns

From: Bimmy Pujari <bimmy.pujari@intel.com>

The existing bpf helper functions to get timestamp return the time
elapsed since system boot. This timestamp is not particularly useful
where epoch timestamp is required or more than one server is involved
and time sync is required. Instead, you want to use CLOCK_REALTIME,
which provides epoch timestamp.
Hence add bfp_ktime_get_real_ns() based around CLOCK_REALTIME.

Signed-off-by: Ashkan Nikravesh <ashkan.nikravesh@intel.com>
Signed-off-by: Bimmy Pujari <bimmy.pujari@intel.com>
---
 drivers/media/rc/bpf-lirc.c    |  2 ++
 include/linux/bpf.h            |  1 +
 include/uapi/linux/bpf.h       |  8 ++++++++
 kernel/bpf/core.c              |  1 +
 kernel/bpf/helpers.c           | 13 +++++++++++++
 kernel/trace/bpf_trace.c       |  2 ++
 tools/include/uapi/linux/bpf.h |  8 ++++++++
 7 files changed, 35 insertions(+)

On Wed, Sep 23, 2020 at 5:03 PM <bimmy.pujari@intel.com> wrote:
>
> From: Bimmy Pujari <bimmy.pujari@intel.com>
>
> The existing bpf helper functions to get timestamp return the time
> elapsed since system boot. This timestamp is not particularly useful
> where epoch timestamp is required or more than one server is involved
> and time sync is required. Instead, you want to use CLOCK_REALTIME,
> which provides epoch timestamp.
> Hence add bfp_ktime_get_real_ns() based around CLOCK_REALTIME.
>
> Signed-off-by: Ashkan Nikravesh <ashkan.nikravesh@intel.com>
> Signed-off-by: Bimmy Pujari <bimmy.pujari@intel.com>
> ---
>  drivers/media/rc/bpf-lirc.c    |  2 ++
>  include/linux/bpf.h            |  1 +
>  include/uapi/linux/bpf.h       |  8 ++++++++
>  kernel/bpf/core.c              |  1 +
>  kernel/bpf/helpers.c           | 13 +++++++++++++
>  kernel/trace/bpf_trace.c       |  2 ++
>  tools/include/uapi/linux/bpf.h |  8 ++++++++
>  7 files changed, 35 insertions(+)
>
> diff --git a/drivers/media/rc/bpf-lirc.c b/drivers/media/rc/bpf-lirc.c
> index 5bb144435c16..1cae0cfdcbaf 100644
> --- a/drivers/media/rc/bpf-lirc.c
> +++ b/drivers/media/rc/bpf-lirc.c
> @@ -103,6 +103,8 @@ lirc_mode2_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
>                 return &bpf_map_peek_elem_proto;
>         case BPF_FUNC_ktime_get_ns:
>                 return &bpf_ktime_get_ns_proto;
> +       case BPF_FUNC_ktime_get_real_ns:
> +               return &bpf_ktime_get_real_ns_proto;
>         case BPF_FUNC_ktime_get_boot_ns:
>                 return &bpf_ktime_get_boot_ns_proto;
>         case BPF_FUNC_tail_call:
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index fc5c901c7542..3179fcc4ef53 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1756,6 +1756,7 @@ extern const struct bpf_func_proto bpf_get_smp_processor_id_proto;
>  extern const struct bpf_func_proto bpf_get_numa_node_id_proto;
>  extern const struct bpf_func_proto bpf_tail_call_proto;
>  extern const struct bpf_func_proto bpf_ktime_get_ns_proto;
> +extern const struct bpf_func_proto bpf_ktime_get_real_ns_proto;
>  extern const struct bpf_func_proto bpf_ktime_get_boot_ns_proto;
>  extern const struct bpf_func_proto bpf_get_current_pid_tgid_proto;
>  extern const struct bpf_func_proto bpf_get_current_uid_gid_proto;
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index a22812561064..198e69a6508d 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -3586,6 +3586,13 @@ union bpf_attr {
>   *             the data in *dst*. This is a wrapper of **copy_from_user**\ ().
>   *     Return
>   *             0 on success, or a negative error in case of failure.
> + *
> + * u64 bpf_ktime_get_real_ns(void)
> + *     Description
> + *             Return the real time in nanoseconds.
> + *             See: **clock_gettime**\ (**CLOCK_REALTIME**)
> + *     Return
> + *             Current *ktime*.
>   */
>  #define __BPF_FUNC_MAPPER(FN)          \
>         FN(unspec),                     \
> @@ -3737,6 +3744,7 @@ union bpf_attr {
>         FN(inode_storage_delete),       \
>         FN(d_path),                     \
>         FN(copy_from_user),             \
> +       FN(ktime_get_real_ns),          \
>         /* */
>
>  /* integer value in 'imm' field of BPF_CALL instruction selects which helper
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index c4811b139caa..af38af5ffc8b 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -2207,6 +2207,7 @@ const struct bpf_func_proto bpf_get_prandom_u32_proto __weak;
>  const struct bpf_func_proto bpf_get_smp_processor_id_proto __weak;
>  const struct bpf_func_proto bpf_get_numa_node_id_proto __weak;
>  const struct bpf_func_proto bpf_ktime_get_ns_proto __weak;
> +const struct bpf_func_proto bpf_ktime_get_real_ns_proto __weak;
>  const struct bpf_func_proto bpf_ktime_get_boot_ns_proto __weak;
>
>  const struct bpf_func_proto bpf_get_current_pid_tgid_proto __weak;
> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> index 5cc7425ee476..776ff58f969d 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -155,6 +155,17 @@ const struct bpf_func_proto bpf_ktime_get_ns_proto = {
>         .ret_type       = RET_INTEGER,
>  };
>
> +BPF_CALL_0(bpf_ktime_get_real_ns)
> +{
> +       /* NMI safe access to clock realtime */
> +       return ktime_get_real_fast_ns();
> +}
> +
> +const struct bpf_func_proto bpf_ktime_get_real_ns_proto = {
> +       .func           = bpf_ktime_get_real_ns,
> +       .gpl_only       = true,

imho should be false, this is normally accessible to userspace code
via syscall, no reason why it should be gpl only for bpf

> +       .ret_type       = RET_INTEGER,
> +};
>  BPF_CALL_0(bpf_ktime_get_boot_ns)
>  {
>         /* NMI safe access to clock boottime */
> @@ -655,6 +666,8 @@ bpf_base_func_proto(enum bpf_func_id func_id)
>                 return &bpf_tail_call_proto;
>         case BPF_FUNC_ktime_get_ns:
>                 return &bpf_ktime_get_ns_proto;
> +       case BPF_FUNC_ktime_get_real_ns:
> +               return &bpf_ktime_get_real_ns_proto;
>         case BPF_FUNC_ktime_get_boot_ns:
>                 return &bpf_ktime_get_boot_ns_proto;
>         case BPF_FUNC_ringbuf_output:
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 36508f46a8db..18b644fff0be 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -1165,6 +1165,8 @@ bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
>                 return &bpf_map_peek_elem_proto;
>         case BPF_FUNC_ktime_get_ns:
>                 return &bpf_ktime_get_ns_proto;
> +       case BPF_FUNC_ktime_get_real_ns:
> +               return &bpf_ktime_get_real_ns_proto;
>         case BPF_FUNC_ktime_get_boot_ns:
>                 return &bpf_ktime_get_boot_ns_proto;

should probably be here to stay alpha sorted more or less (also
applies to other places)

>         case BPF_FUNC_tail_call:
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index a22812561064..198e69a6508d 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -3586,6 +3586,13 @@ union bpf_attr {
>   *             the data in *dst*. This is a wrapper of **copy_from_user**\ ().
>   *     Return
>   *             0 on success, or a negative error in case of failure.
> + *
> + * u64 bpf_ktime_get_real_ns(void)
> + *     Description
> + *             Return the real time in nanoseconds.
> + *             See: **clock_gettime**\ (**CLOCK_REALTIME**)
> + *     Return
> + *             Current *ktime*.
>   */
>  #define __BPF_FUNC_MAPPER(FN)          \
>         FN(unspec),                     \
> @@ -3737,6 +3744,7 @@ union bpf_attr {
>         FN(inode_storage_delete),       \
>         FN(d_path),                     \
>         FN(copy_from_user),             \
> +       FN(ktime_get_real_ns),          \
>         /* */
>
>  /* integer value in 'imm' field of BPF_CALL instruction selects which helper
> --
> 2.17.1
>
Maciej Żenczykowski, Kernel Networking Developer @ Google

On 9/23/20 7:19 PM, Maciej Żenczykowski wrote:
>> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
>> index 5cc7425ee476..776ff58f969d 100644
>> --- a/kernel/bpf/helpers.c
>> +++ b/kernel/bpf/helpers.c
>> @@ -155,6 +155,17 @@ const struct bpf_func_proto bpf_ktime_get_ns_proto = {
>>         .ret_type       = RET_INTEGER,
>>  };
>>
>> +BPF_CALL_0(bpf_ktime_get_real_ns)
>> +{
>> +       /* NMI safe access to clock realtime */
>> +       return ktime_get_real_fast_ns();
>> +}
>> +
>> +const struct bpf_func_proto bpf_ktime_get_real_ns_proto = {
>> +       .func           = bpf_ktime_get_real_ns,
>> +       .gpl_only       = true,
> 
> imho should be false, this is normally accessible to userspace code
> via syscall, no reason why it should be gpl only for bpf
> 

agreed, no reason for the bpf hook to be gpl_only.

Glad to see the v2 of this patch; I wondered what happened to this helper.

-----Original Message-----
From: David Ahern <dsahern@gmail.com> 
Sent: Wednesday, September 23, 2020 7:19 PM
To: Maciej Żenczykowski <maze@google.com>; Pujari, Bimmy <bimmy.pujari@intel.com>
Cc: bpf <bpf@vger.kernel.org>; Linux NetDev <netdev@vger.kernel.org>; mchehab@kernel.org; Alexei Starovoitov <ast@kernel.org>; Daniel Borkmann <daniel@iogearbox.net>; Martin Lau <kafai@fb.com>; Nikravesh, Ashkan <ashkan.nikravesh@intel.com>
Subject: Re: [PATCH bpf-next v2 1/2] bpf: Add bpf_ktime_get_real_ns

On 9/23/20 7:19 PM, Maciej Żenczykowski wrote:
>> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c index 
>> 5cc7425ee476..776ff58f969d 100644
>> --- a/kernel/bpf/helpers.c
>> +++ b/kernel/bpf/helpers.c
>> @@ -155,6 +155,17 @@ const struct bpf_func_proto bpf_ktime_get_ns_proto = {
>>         .ret_type       = RET_INTEGER,
>>  };
>>
>> +BPF_CALL_0(bpf_ktime_get_real_ns)
>> +{
>> +       /* NMI safe access to clock realtime */
>> +       return ktime_get_real_fast_ns(); }
>> +
>> +const struct bpf_func_proto bpf_ktime_get_real_ns_proto = {
>> +       .func           = bpf_ktime_get_real_ns,
>> +       .gpl_only       = true,
> 
> imho should be false, this is normally accessible to userspace code 
> via syscall, no reason why it should be gpl only for bpf
> 

agreed, no reason for the bpf hook to be gpl_only.

Glad to see the v2 of this patch; I wondered what happened to this helper.
BP: Thanks Maciej & Ahern for taking time to look at it. I will update the changes suggested shortly.