Re: [PATCH bpf-next v1 05/13] tools/libbpf: Add support in libbpf for BPF_PROG_TYPE_LSM

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Fri, Dec 20, 2019 at 7:43 AM KP Singh <kpsingh@chromium.org> wrote:
>
> From: KP Singh <kpsingh@google.com>
>
> Update the libbpf library with functionality to load and
> attach a program type BPF_PROG_TYPE_LSM, currently with
> only one expected attach type BPF_LSM_MAC.
>
> Signed-off-by: KP Singh <kpsingh@google.com>
> ---
>  tools/lib/bpf/bpf.c           |  2 +-
>  tools/lib/bpf/bpf.h           |  6 +++++
>  tools/lib/bpf/libbpf.c        | 44 +++++++++++++++++++++--------------
>  tools/lib/bpf/libbpf.h        |  2 ++
>  tools/lib/bpf/libbpf.map      |  6 +++++
>  tools/lib/bpf/libbpf_probes.c |  1 +
>  6 files changed, 43 insertions(+), 18 deletions(-)
>
> diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
> index 98596e15390f..9c6fb083f7de 100644
> --- a/tools/lib/bpf/bpf.c
> +++ b/tools/lib/bpf/bpf.c
> @@ -228,7 +228,7 @@ int bpf_load_program_xattr(const struct bpf_load_program_attr *load_attr,
>         memset(&attr, 0, sizeof(attr));
>         attr.prog_type = load_attr->prog_type;
>         attr.expected_attach_type = load_attr->expected_attach_type;
> -       if (attr.prog_type == BPF_PROG_TYPE_TRACING) {
> +       if (needs_btf_attach(attr.prog_type)) {
>                 attr.attach_btf_id = load_attr->attach_btf_id;
>                 attr.attach_prog_fd = load_attr->attach_prog_fd;
>         } else {
> diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
> index 3c791fa8e68e..df2a00ff349f 100644
> --- a/tools/lib/bpf/bpf.h
> +++ b/tools/lib/bpf/bpf.h
> @@ -177,6 +177,12 @@ LIBBPF_API int bpf_task_fd_query(int pid, int fd, __u32 flags, char *buf,
>                                  __u32 *buf_len, __u32 *prog_id, __u32 *fd_type,
>                                  __u64 *probe_offset, __u64 *probe_addr);
>
> +static inline bool needs_btf_attach(enum bpf_prog_type prog_type)
> +{
> +       return (prog_type == BPF_PROG_TYPE_TRACING ||
> +               prog_type == BPF_PROG_TYPE_LSM);
> +}
> +

This doesn't have to be a public API, right? It also doesn't follow
naming conventions of libbpf APIs. Let's just move it into
libbpf_internal.h, given it's used in few files.

Also, Martin's patches add STRUCT_OPS, which do need btf_attach, but
don't set attach_prog_fd. So maybe something like
libbpf_need_attach_prog_btf() for a name to be a bit more specific?


>  #ifdef __cplusplus
>  } /* extern "C" */
>  #endif
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index b20f82e58989..b0b27d8e5a37 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -3738,7 +3738,7 @@ load_program(struct bpf_program *prog, struct bpf_insn *insns, int insns_cnt,
>         load_attr.insns = insns;
>         load_attr.insns_cnt = insns_cnt;
>         load_attr.license = license;
> -       if (prog->type == BPF_PROG_TYPE_TRACING) {
> +       if (needs_btf_attach(prog->type)) {
>                 load_attr.attach_prog_fd = prog->attach_prog_fd;
>                 load_attr.attach_btf_id = prog->attach_btf_id;
>         } else {
> @@ -3983,7 +3983,7 @@ __bpf_object__open(const char *path, const void *obj_buf, size_t obj_buf_sz,
>
>                 bpf_program__set_type(prog, prog_type);
>                 bpf_program__set_expected_attach_type(prog, attach_type);
> -               if (prog_type == BPF_PROG_TYPE_TRACING) {
> +               if (needs_btf_attach(prog_type)) {
>                         err = libbpf_find_attach_btf_id(prog->section_name,
>                                                         attach_type,
>                                                         attach_prog_fd);
> @@ -4933,6 +4933,7 @@ bool bpf_program__is_##NAME(const struct bpf_program *prog)       \
>  }                                                              \
>
>  BPF_PROG_TYPE_FNS(socket_filter, BPF_PROG_TYPE_SOCKET_FILTER);
> +BPF_PROG_TYPE_FNS(lsm, BPF_PROG_TYPE_LSM);
>  BPF_PROG_TYPE_FNS(kprobe, BPF_PROG_TYPE_KPROBE);
>  BPF_PROG_TYPE_FNS(sched_cls, BPF_PROG_TYPE_SCHED_CLS);
>  BPF_PROG_TYPE_FNS(sched_act, BPF_PROG_TYPE_SCHED_ACT);
> @@ -5009,6 +5010,8 @@ static const struct {
>         BPF_PROG_SEC("lwt_out",                 BPF_PROG_TYPE_LWT_OUT),
>         BPF_PROG_SEC("lwt_xmit",                BPF_PROG_TYPE_LWT_XMIT),
>         BPF_PROG_SEC("lwt_seg6local",           BPF_PROG_TYPE_LWT_SEG6LOCAL),
> +       BPF_PROG_BTF("lsm/",                    BPF_PROG_TYPE_LSM,
> +                                               BPF_LSM_MAC),

Is is supposed to be attachable same as BPF_PROG_TYPE_TRACING
programs? If yes, please define auto-attaching function, similar to
SEC_DEF("raw_tp") few lines below this one.

>         BPF_APROG_SEC("cgroup_skb/ingress",     BPF_PROG_TYPE_CGROUP_SKB,
>                                                 BPF_CGROUP_INET_INGRESS),
>         BPF_APROG_SEC("cgroup_skb/egress",      BPF_PROG_TYPE_CGROUP_SKB,
> @@ -5119,32 +5122,39 @@ int libbpf_prog_type_by_name(const char *name, enum bpf_prog_type *prog_type,
>         return -ESRCH;
>  }
>
> -#define BTF_PREFIX "btf_trace_"
> +static inline int __btf__typdef_with_prefix(struct btf *btf, const char *name,

typo: typdef -> typedef

But actually let's generalize it to pass BTF_KIND as another param, I
think I have a need for this (we might want to do that for structs,
not just typedef->func_proto).
Following btf__find_by_name_kind() naming, it probably should be
called btf__find_by_prefix_kind()?

> +                                           const char *prefix)
> +{
> +
> +       size_t prefix_len = strlen(prefix);
> +       char btf_type_name[128];
> +
> +       strcpy(btf_type_name, prefix);
> +       strncat(btf_type_name, name, sizeof(btf_type_name) - (prefix_len + 1));

at this point snprintf(btf_type_name, "%s%.*%s", prefix,
sizeof(btf_type_name) - prefix_len - 1, name) looks like a better and
cleaner alternative.

> +       return btf__find_by_name_kind(btf, btf_type_name, BTF_KIND_TYPEDEF);
> +}
> +
> +#define BTF_TRACE_PREFIX "btf_trace_"
> +#define BTF_LSM_PREFIX "lsm_btf_"
> +

[...]