Re: [PATCH v1 2/4] perf trace: Migrate BPF augmentation to use a skeleton

[Arnaldo Carvalho de Melo <acme@kernel.org>]

Em Wed, Aug 16, 2023 at 10:11:11AM -0300, Arnaldo Carvalho de Melo escreveu:
> Just taking notes about things to work on top of what is in
> tmp.perf-tools-next, that will move to perf-tools-next soon:
> 
> We need to make these libbpf error messages appear only in verbose mode,
> and probably have a hint about unprivileged BPF, a quick attempt failed
> after several attempts at getting privileges :-\
> 
> Probably attaching to tracepoints is off limits to !root even with
> /proc/sys/kernel/unprivileged_bpf_disabled set to zero.

yep, the libbpf sys_bpf call to check if it could load a basic BPF
bytecode (prog_type=BPF_PROG_TYPE_SOCKET_FILTER, insn_cnt=2) succeeds,
but then, later we manage to create the maps, etc to then stumble on 

bpf(BPF_MAP_CREATE, {map_type=BPF_MAP_TYPE_PERCPU_ARRAY, key_size=4, value_size=8272, max_entries=1, map_flags=0, inner_map_fd=0, map_name="augmented_args_", map_ifindex=0, btf_fd=0, btf_key_type_id=0, btf_value_type_id=0, btf_vmlinux_value_type_id=0, map_extra=0}, 72) = 7
bpf(BPF_BTF_LOAD, {btf="\237\353\1\0\30\0\0\0\0\0\0\0000\0\0\0000\0\0\0\t\0\0\0\1\0\0\0\0\0\0\1"..., btf_log_buf=NULL, btf_size=81, btf_log_size=0, btf_log_level=0}, 32) = -1 EPERM (Operation not permitted)

and:

bpf(BPF_PROG_LOAD, {prog_type=BPF_PROG_TYPE_TRACEPOINT, insn_cnt=2, insns=0x1758340, license="GPL", log_level=0, log_size=0, log_buf=NULL, kern_version=KERNEL_VERSION(6, 4, 7), prog_flags=0, prog_name="syscall_unaugme", prog_ifindex=0, expected_attach_type=BPF_CGROUP_INET_INGRESS, prog_btf_fd=0, func_info_rec_size=0, func_info=NULL, func_info_cnt=0, line_info_rec_size=0, line_info=NULL, line_info_cnt=0, attach_btf_id=0, attach_prog_fd=0, fd_array=NULL}, 144) = -1 EPERM (Operation not permitted)

So 'perf trace' should just not try to load the augmented_raw_syscalls
BPF skel for !root.

- Arnaldo

[acme@quaco perf-tools-next]$ strace -e bpf perf trace -vv -e open* sleep 1
bpf(BPF_PROG_LOAD, {prog_type=BPF_PROG_TYPE_SOCKET_FILTER, insn_cnt=2, insns=0x7ffe95185300, license="GPL", log_level=0, log_size=0, log_buf=NULL, kern_version=KERNEL_VERSION(0, 0, 0), prog_flags=0, prog_name="", prog_ifindex=0, expected_attach_type=BPF_CGROUP_INET_INGRESS, prog_btf_fd=0, func_info_rec_size=0, func_info=NULL, func_info_cnt=0, line_info_rec_size=0, line_info=NULL, line_info_cnt=0, attach_btf_id=0, attach_prog_fd=0}, 116) = 3
bpf(BPF_PROG_LOAD, {prog_type=BPF_PROG_TYPE_SOCKET_FILTER, insn_cnt=2, insns=0x7ffe951854a0, license="GPL", log_level=0, log_size=0, log_buf=NULL, kern_version=KERNEL_VERSION(0, 0, 0), prog_flags=0, prog_name="", prog_ifindex=0, expected_attach_type=BPF_CGROUP_INET_INGRESS, prog_btf_fd=0, func_info_rec_size=0, func_info=NULL, func_info_cnt=0, line_info_rec_size=0, line_info=NULL, line_info_cnt=0, attach_btf_id=0, attach_prog_fd=0, fd_array=NULL}, 144) = 3
bpf(BPF_BTF_LOAD, {btf="\237\353\1\0\30\0\0\0\0\0\0\0\20\0\0\0\20\0\0\0\5\0\0\0\1\0\0\0\0\0\0\1"..., btf_log_buf=NULL, btf_size=45, btf_log_size=0, btf_log_level=0}, 32) = -1 EPERM (Operation not permitted)
bpf(BPF_PROG_LOAD, {prog_type=BPF_PROG_TYPE_SOCKET_FILTER, insn_cnt=2, insns=0x7ffe95185110, license="GPL", log_level=0, log_size=0, log_buf=NULL, kern_version=KERNEL_VERSION(0, 0, 0), prog_flags=0, prog_name="libbpf_nametest"}, 64) = 3
bpf(BPF_MAP_CREATE, {map_type=BPF_MAP_TYPE_HASH, key_size=4, value_size=1, max_entries=64, map_flags=0, inner_map_fd=0, map_name="pids_filtered", map_ifindex=0, btf_fd=0, btf_key_type_id=0, btf_value_type_id=0, btf_vmlinux_value_type_id=0, map_extra=0}, 72) = 3
bpf(BPF_MAP_CREATE, {map_type=BPF_MAP_TYPE_PROG_ARRAY, key_size=4, value_size=4, max_entries=512, map_flags=0, inner_map_fd=0, map_name="syscalls_sys_en", map_ifindex=0, btf_fd=0, btf_key_type_id=0, btf_value_type_id=0, btf_vmlinux_value_type_id=0, map_extra=0}, 72) = 4
bpf(BPF_MAP_CREATE, {map_type=BPF_MAP_TYPE_PROG_ARRAY, key_size=4, value_size=4, max_entries=512, map_flags=0, inner_map_fd=0, map_name="syscalls_sys_ex", map_ifindex=0, btf_fd=0, btf_key_type_id=0, btf_value_type_id=0, btf_vmlinux_value_type_id=0, map_extra=0}, 72) = 5
bpf(BPF_MAP_CREATE, {map_type=BPF_MAP_TYPE_PERF_EVENT_ARRAY, key_size=4, value_size=4, max_entries=4096, map_flags=0, inner_map_fd=0, map_name="__augmented_sys", map_ifindex=0, btf_fd=0, btf_key_type_id=0, btf_value_type_id=0, btf_vmlinux_value_type_id=0, map_extra=0}, 72) = 6
bpf(BPF_MAP_CREATE, {map_type=BPF_MAP_TYPE_PERCPU_ARRAY, key_size=4, value_size=8272, max_entries=1, map_flags=0, inner_map_fd=0, map_name="augmented_args_", map_ifindex=0, btf_fd=0, btf_key_type_id=0, btf_value_type_id=0, btf_vmlinux_value_type_id=0, map_extra=0}, 72) = 7
bpf(BPF_BTF_LOAD, {btf="\237\353\1\0\30\0\0\0\0\0\0\0000\0\0\0000\0\0\0\t\0\0\0\1\0\0\0\0\0\0\1"..., btf_log_buf=NULL, btf_size=81, btf_log_size=0, btf_log_level=0}, 32) = -1 EPERM (Operation not permitted)
bpf(BPF_PROG_LOAD, {prog_type=BPF_PROG_TYPE_TRACEPOINT, insn_cnt=2, insns=0x1758340, license="GPL", log_level=0, log_size=0, log_buf=NULL, kern_version=KERNEL_VERSION(6, 4, 7), prog_flags=0, prog_name="syscall_unaugme", prog_ifindex=0, expected_attach_type=BPF_CGROUP_INET_INGRESS, prog_btf_fd=0, func_info_rec_size=0, func_info=NULL, func_info_cnt=0, line_info_rec_size=0, line_info=NULL, line_info_cnt=0, attach_btf_id=0, attach_prog_fd=0, fd_array=NULL}, 144) = -1 EPERM (Operation not permitted)
bpf(BPF_PROG_LOAD, {prog_type=BPF_PROG_TYPE_TRACEPOINT, insn_cnt=2, insns=0x1758340, license="GPL", log_level=1, log_size=16777215, log_buf="", kern_version=KERNEL_VERSION(6, 4, 7), prog_flags=0, prog_name="syscall_unaugme", prog_ifindex=0, expected_attach_type=BPF_CGROUP_INET_INGRESS, prog_btf_fd=0, func_info_rec_size=0, func_info=NULL, func_info_cnt=0, line_info_rec_size=0, line_info=NULL, line_info_cnt=0, attach_btf_id=0, attach_prog_fd=0, fd_array=NULL}, 144) = -1 EPERM (Operation not permitted)
libbpf: prog 'syscall_unaugmented': BPF program load failed: Operation not permitted
libbpf: prog 'syscall_unaugmented': failed to load: -1
libbpf: failed to load object 'augmented_raw_syscalls_bpf'
libbpf: failed to load BPF skeleton 'augmented_raw_syscalls_bpf': -1
Failed to load augmented syscalls BPF skeleton: Operation not permitted
Using CPUID GenuineIntel-6-8E-A
intel_pt default config: tsc,mtc,mtc_period=3,psb_period=3,pt,branch
Error:	No permissions to read /sys/kernel/tracing//events/raw_syscalls/sys_(enter|exit)
Hint:	Try 'sudo mount -o remount,mode=755 /sys/kernel/tracing/'

+++ exited with 255 +++
[acme@quaco perf-tools-next]$