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eBPF Program Types

Inspektor Gadget automatically loads and attaches the eBPF programs contained in a gadget. This document describes the different types that are supported and specific details about them. The section name specifies the type of the program and the target they should be attached to.

Program Types​

Kprobes / Kretprobes​

The section name must use the kprobe/<function_name> or kretprobe/<function_name> formats. <function_name> is the kernel function that the kprobe will be attached to.

Tracepoints​

The section name must use the tracepoint/<tracepoint_name>. <tracepoint_name> is one of the available tracepoints on /sys/kernel/debug/tracing/events.

Socket Filter​

The section name must start with socket. Socket programs are attached to all network namespaces matching the filter configuration when running the gadget.

Tracing​

Currently we support some iterators and fentry/fexit programs.

Iterators​

The section name must use iter/<iter_type>. ig supports the following <iter_type>:

  • ksym
  • task
  • task_file
  • tcp
  • udp

tcp and udp iterators are invoked in different network namespaces matching the filter configuration when running the gadget.

You can find the list of iterator types supported by Linux with:

  • git grep -w ^DEFINE_BPF_ITER_FUNC in the Linux sources (16 types as of Linux 6.9)
  • sudo bpftool btf dump id 1 format c |grep 'struct bpf_iter__' in the current kernel

Fentry / Fexit​

The section name must use the fentry/<function_name or fexit/<function_name>. As in kprobes, <function_name> is the kernel function that the kprobe will be attached to.

Raw Tracepoints​

TODO!

SchedCLS​

The section name must use the classifier/<ingress|egress>/<program_name> format. SchedCLS programs are attached to the peer of the networking interface of the containers on the host according to the filtering configuration.

Inspektor Gadget supports running multiple gadgets that use SchedCLS programs at the same time. Programs must return TC_ACT_UNSPEC in order to allow the packet to be processed by other gadgets. The order of execution of the programs is not deterministic, this is something we could visit later on.

Uprobes / Uretprobes​

The section name must use the <prog_type>/<file_path>:<symbol> format. <prog_type> must be either uprobe or uretprobe. <file_path> is the absolute path of an executable or a library, that the uprobe will be attached to. For common libraries, <file_path> can also be the library's name, such as libc. <symbol> is a debugging symbol that can be found in the file mentioned above.

User-Level Statically Defined Tracing (USDT)​

The section name must use the usdt/<file_path>:<providerName>:<probeName> format. <file_path> can be either an absolute path or a library name, same as the field in Uprobe. <providerName> and <probeName> are two fields that can jointly identify a USDT trace point.

Tracing with Linux Security Modules (LSM)​

The section name must use the lsm/<hook> format. The hook points could be found in <include/linux/lsm_hook_defs.h>.

Disabling Programs​

You can disable a program by using gadget_program_disabled as the program target. For example:

SEC("kprobe/gadget_program_disabled")
int BPF_KPROBE(foo, args...)
{
	return 0;
}