linux-kernel - Re: [PATCH v2 bpf-next] bpf: Allow some trace helpers for all prog types

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Message-ID: <CAEf4BzbJ0eaiiaCukaJV0JmrzF6fsbwOxszQUV3pL+MAJT25rw@mail.gmail.com>
Date: Thu, 1 May 2025 11:11:52 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Feng Yang <yangfeng59949@....com>
Cc: martin.lau@...ux.dev, ast@...nel.org, daniel@...earbox.net, 
	andrii@...nel.org, eddyz87@...il.com, song@...nel.org, 
	yonghong.song@...ux.dev, john.fastabend@...il.com, kpsingh@...nel.org, 
	sdf@...ichev.me, haoluo@...gle.com, jolsa@...nel.org, 
	mattbobrowski@...gle.com, rostedt@...dmis.org, mhiramat@...nel.org, 
	mathieu.desnoyers@...icios.com, davem@...emloft.net, bpf@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org, 
	netdev@...r.kernel.org, htejun@...com
Subject: Re: [PATCH v2 bpf-next] bpf: Allow some trace helpers for all prog types

On Sat, Apr 26, 2025 at 11:39 PM Feng Yang <yangfeng59949@....com> wrote:
>
> From: Feng Yang <yangfeng@...inos.cn>
>
> if it works under NMI and doesn't use any context-dependent things,
> should be fine for any program type. The detailed discussion is in [1].
>
> [1] https://lore.kernel.org/all/CAEf4Bza6gK3dsrTosk6k3oZgtHesNDSrDd8sdeQ-GiS6oJixQg@mail.gmail.com/
>
> Suggested-by: Andrii Nakryiko <andrii.nakryiko@...il.com>
> Signed-off-by: Feng Yang <yangfeng@...inos.cn>
> ---
> Changes in v2:
> - not expose compat probe read APIs to more program types.
> - Remove the prog->sleepable check added for copy_from_user,
> - or the summarization_freplace/might_sleep_with_might_sleep test will fail with the error "program of this type cannot use helper bpf_copy_from_user"
> - Link to v1: https://lore.kernel.org/all/20250425080032.327477-1-yangfeng59949@163.com/
> ---
>  kernel/bpf/cgroup.c      |  6 ------
>  kernel/bpf/helpers.c     | 38 +++++++++++++++++++++++++++++++++++++
>  kernel/trace/bpf_trace.c | 41 ++++------------------------------------
>  net/core/filter.c        |  2 --
>  4 files changed, 42 insertions(+), 45 deletions(-)
>
> diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
> index 84f58f3d028a..dbdad5f42761 100644
> --- a/kernel/bpf/cgroup.c
> +++ b/kernel/bpf/cgroup.c
> @@ -2607,16 +2607,10 @@ const struct bpf_func_proto *
>  cgroup_current_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
>  {
>         switch (func_id) {
> -       case BPF_FUNC_get_current_uid_gid:
> -               return &bpf_get_current_uid_gid_proto;
> -       case BPF_FUNC_get_current_comm:
> -               return &bpf_get_current_comm_proto;
>  #ifdef CONFIG_CGROUP_NET_CLASSID
>         case BPF_FUNC_get_cgroup_classid:
>                 return &bpf_get_cgroup_classid_curr_proto;
>  #endif

this is the only one left, and again, it's just current-dependent, so
I'd just move this into base set and got rid of
cgroup_current_func_proto altogether (there are 5 callers, let's clean
them up)

> -       case BPF_FUNC_current_task_under_cgroup:
> -               return &bpf_current_task_under_cgroup_proto;
>         default:
>                 return NULL;
>         }
> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> index e3a2662f4e33..a01a2e55e17d 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -23,6 +23,7 @@
>  #include <linux/btf_ids.h>
>  #include <linux/bpf_mem_alloc.h>
>  #include <linux/kasan.h>
> +#include <linux/bpf_verifier.h>

why do we need this include?

[...]

> @@ -2057,6 +2074,27 @@ bpf_base_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
>                 return bpf_get_trace_vprintk_proto();
>         case BPF_FUNC_perf_event_read_value:
>                 return bpf_get_perf_event_read_value_proto();
> +       case BPF_FUNC_perf_event_read:
> +               return &bpf_perf_event_read_proto;
> +       case BPF_FUNC_send_signal:
> +               return &bpf_send_signal_proto;
> +       case BPF_FUNC_send_signal_thread:
> +               return &bpf_send_signal_thread_proto;
> +       case BPF_FUNC_get_task_stack:
> +               return prog->sleepable ? &bpf_get_task_stack_sleepable_proto
> +                                      : &bpf_get_task_stack_proto;
> +       case BPF_FUNC_task_storage_get:
> +               if (bpf_prog_check_recur(prog))
> +                       return &bpf_task_storage_get_recur_proto;
> +               return &bpf_task_storage_get_proto;
> +       case BPF_FUNC_task_storage_delete:
> +               if (bpf_prog_check_recur(prog))
> +                       return &bpf_task_storage_delete_recur_proto;
> +               return &bpf_task_storage_delete_proto;

task_storage_{get,delete} probably should be guarded just by CAP_BPF,
no need for CAP_PERFMON, IMO. Can you please move them up a bit?

Also, we should probably get rid of bpf_scx_get_func_proto() in
kernel/sched/ext.c, given it only adds these two on top of the base
set? But that's probably a separate patch against sched_ext tree?
cc'ing Tejun

pw-bot: cr

> +       case BPF_FUNC_get_branch_snapshot:
> +               return &bpf_get_branch_snapshot_proto;
> +       case BPF_FUNC_find_vma:
> +               return &bpf_find_vma_proto;
>         default:
>                 return NULL;
>         }

[...]