[PATCH 6.1 093/473] bpftool: Fix missing pids during link show

Greg Kroah-Hartman
2024-06-06T14:13:36Z

From: Yonghong Song <yonghong.song@linux.dev>

[ Upstream commit fe879bb42f8a6513ed18e9d22efb99cb35590201 ]

Current 'bpftool link' command does not show pids, e.g.,
$ tools/build/bpftool/bpftool link
...
4: tracing prog 23
prog_type lsm attach_type lsm_mac
target_obj_id 1 target_btf_id 31320

Hack the following change to enable normal libbpf debug output,
# --- a/tools/bpf/bpftool/pids.c
# +++ b/tools/bpf/bpftool/pids.c
# @@ -121,9 +121,9 @@ int build_obj_refs_table(struct hashmap **map, enum bpf_obj_type type)
# /* we don't want output polluted with libbpf errors if bpf_iter is not
# * supported
# */
# - default_print = libbpf_set_print(libbpf_print_none);
# + /* default_print = libbpf_set_print(libbpf_print_none); */
# err = pid_iter_bpf__load(skel);
# - libbpf_set_print(default_print);
# + /* libbpf_set_print(default_print); */

Rerun the above bpftool command:
$ tools/build/bpftool/bpftool link
libbpf: prog 'iter': BPF program load failed: Permission denied
libbpf: prog 'iter': -- BEGIN PROG LOAD LOG --
0: R1=ctx() R10=fp0
; struct task_struct *task = ctx->task; @ pid_iter.bpf.c:69
0: (79) r6 = *(u64 *)(r1 +8) ; R1=ctx() R6_w=ptr_or_null_task_struct(id=1)
; struct file *file = ctx->file; @ pid_iter.bpf.c:68
...
; struct bpf_link *link = (struct bpf_link *) file->private_data; @ pid_iter.bpf.c:103
80: (79) r3 = *(u64 *)(r8 +432) ; R3_w=scalar() R8=ptr_file()
; if (link->type == bpf_core_enum_value(enum bpf_link_type___local, @ pid_iter.bpf.c:105
81: (61) r1 = *(u32 *)(r3 +12)
R3 invalid mem access 'scalar'
processed 39 insns (limit 1000000) max_states_per_insn 0 total_states 3 peak_states 3 mark_read 2
-- END PROG LOAD LOG --
libbpf: prog 'iter': failed to load: -13
...

The 'file->private_data' returns a 'void' type and this caused subsequent 'link->type'
(insn #81) failed in verification.

To fix the issue, restore the previous BPF_CORE_READ so old kernels can also work.
With this patch, the 'bpftool link' runs successfully with 'pids'.
$ tools/build/bpftool/bpftool link
...
4: tracing prog 23
prog_type lsm attach_type lsm_mac
target_obj_id 1 target_btf_id 31320
pids systemd(1)

Fixes: 44ba7b30e84f ("bpftool: Use a local copy of BPF_LINK_TYPE_PERF_EVENT in pid_iter.bpf.c")
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Tested-by: Quentin Monnet <quentin@isovalent.com>
Reviewed-by: Quentin Monnet <quentin@isovalent.com>
Link: https://lore.kernel.org/bpf/20240312023249.3776718-1-yonghong.song@linux.dev
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
tools/bpf/bpftool/skeleton/pid_iter.bpf.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/bpf/bpftool/skeleton/pid_iter.bpf.c b/tools/bpf/bpftool/skeleton/pid_iter.bpf.c
index 26004f0c5a6ae..7bdbcac3cf628 100644
--- a/tools/bpf/bpftool/skeleton/pid_iter.bpf.c
+++ b/tools/bpf/bpftool/skeleton/pid_iter.bpf.c
@@ -102,8 +102,8 @@ int iter(struct bpf_iter__task_file *ctx)
BPF_LINK_TYPE_PERF_EVENT___local)) {
struct bpf_link *link = (struct bpf_link *) file->private_data;

- if (link->type == bpf_core_enum_value(enum bpf_link_type___local,
- BPF_LINK_TYPE_PERF_EVENT___local)) {
+ if (BPF_CORE_READ(link, type) == bpf_core_enum_value(enum bpf_link_type___local,
+ BPF_LINK_TYPE_PERF_EVENT___local)) {
e.has_bpf_cookie = true;
e.bpf_cookie = get_bpf_cookie(link);
}
--
2.43.0