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bc1a85977b
BPF tail call uses the BPF_MAP_TYPE_PROG_ARRAY type map for calling
into other BPF programs and this PROG_ARRAY should be filled prior to
use. Currently, samples with the PROG_ARRAY type MAP fill this program
array with bpf_load. For bpf_load to fill this map, kernel BPF program
must specify the section with specific format of <prog_type>/<array_idx>
(e.g. SEC("socket/0"))
But by using libbpf instead of bpf_load, user program can specify which
programs should be added to PROG_ARRAY. The advantage of this approach
is that you can selectively add only the programs you want, rather than
adding all of them to PROG_ARRAY, and it's much more intuitive than the
traditional approach.
This commit refactors user programs with the PROG_ARRAY type MAP with
libbpf instead of using bpf_load.
Signed-off-by: Daniel T. Lee <danieltimlee@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20200516040608.1377876-4-danieltimlee@gmail.com
102 lines
2.4 KiB
C
102 lines
2.4 KiB
C
// SPDX-License-Identifier: GPL-2.0
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#include <stdio.h>
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#include <stdlib.h>
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#include <unistd.h>
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#include <linux/filter.h>
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#include <linux/seccomp.h>
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#include <sys/prctl.h>
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#include <bpf/bpf.h>
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#include <bpf/libbpf.h>
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#include <sys/resource.h>
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#include "trace_helpers.h"
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#ifdef __mips__
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#define MAX_ENTRIES 6000 /* MIPS n64 syscalls start at 5000 */
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#else
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#define MAX_ENTRIES 1024
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#endif
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/* install fake seccomp program to enable seccomp code path inside the kernel,
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* so that our kprobe attached to seccomp_phase1() can be triggered
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*/
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static void install_accept_all_seccomp(void)
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{
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struct sock_filter filter[] = {
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BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW),
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};
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struct sock_fprog prog = {
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.len = (unsigned short)(sizeof(filter)/sizeof(filter[0])),
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.filter = filter,
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};
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if (prctl(PR_SET_SECCOMP, 2, &prog))
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perror("prctl");
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}
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int main(int ac, char **argv)
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{
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struct rlimit r = {RLIM_INFINITY, RLIM_INFINITY};
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struct bpf_link *link = NULL;
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struct bpf_program *prog;
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struct bpf_object *obj;
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int key, fd, progs_fd;
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char filename[256];
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const char *title;
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FILE *f;
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setrlimit(RLIMIT_MEMLOCK, &r);
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snprintf(filename, sizeof(filename), "%s_kern.o", argv[0]);
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obj = bpf_object__open_file(filename, NULL);
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if (libbpf_get_error(obj)) {
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fprintf(stderr, "ERROR: opening BPF object file failed\n");
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return 0;
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}
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prog = bpf_object__find_program_by_name(obj, "bpf_prog1");
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if (!prog) {
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printf("finding a prog in obj file failed\n");
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goto cleanup;
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}
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/* load BPF program */
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if (bpf_object__load(obj)) {
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fprintf(stderr, "ERROR: loading BPF object file failed\n");
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goto cleanup;
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}
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link = bpf_program__attach(prog);
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if (libbpf_get_error(link)) {
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fprintf(stderr, "ERROR: bpf_program__attach failed\n");
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link = NULL;
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goto cleanup;
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}
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progs_fd = bpf_object__find_map_fd_by_name(obj, "progs");
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if (progs_fd < 0) {
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fprintf(stderr, "ERROR: finding a map in obj file failed\n");
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goto cleanup;
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}
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bpf_object__for_each_program(prog, obj) {
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title = bpf_program__title(prog, false);
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/* register only syscalls to PROG_ARRAY */
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if (sscanf(title, "kprobe/%d", &key) != 1)
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continue;
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fd = bpf_program__fd(prog);
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bpf_map_update_elem(progs_fd, &key, &fd, BPF_ANY);
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}
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install_accept_all_seccomp();
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f = popen("dd if=/dev/zero of=/dev/null count=5", "r");
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(void) f;
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read_trace_pipe();
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cleanup:
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bpf_link__destroy(link);
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bpf_object__close(obj);
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return 0;
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}
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