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samples/bpf: bpf_tail_call example for tracing

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kprobe example that demonstrates how future seccomp programs may look like.
It attaches to seccomp_phase1() function and tail-calls other BPF programs
depending on syscall number.

Existing optimized classic BPF seccomp programs generated by Chrome look like:
if (sd.nr < 121) {
  if (sd.nr < 57) {
    if (sd.nr < 22) {
      if (sd.nr < 7) {
        if (sd.nr < 4) {
          if (sd.nr < 1) {
            check sys_read
          } else {
            if (sd.nr < 3) {
              check sys_write and sys_open
            } else {
              check sys_close
            }
          }
        } else {
      } else {
    } else {
  } else {
} else {
}

the future seccomp using native eBPF may look like:
  bpf_tail_call(&sd, &syscall_jmp_table, sd.nr);
which is simpler, faster and leaves more room for per-syscall checks.

Usage:
$ sudo ./tracex5
<...>-366   [001] d...     4.870033: : read(fd=1, buf=00007f6d5bebf000, size=771)
<...>-369   [003] d...     4.870066: : mmap
<...>-369   [003] d...     4.870077: : syscall=110 (one of get/set uid/pid/gid)
<...>-369   [003] d...     4.870089: : syscall=107 (one of get/set uid/pid/gid)
   sh-369   [000] d...     4.891740: : read(fd=0, buf=00000000023d1000, size=512)
   sh-369   [000] d...     4.891747: : write(fd=1, buf=00000000023d3000, size=512)
   sh-369   [000] d...     4.891747: : read(fd=1, buf=00000000023d3000, size=512)

Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Alexei Starovoitov
2015-05-19 16:59:05 -07:00
committed by David S. Miller
parent b52f00e6a7
commit 5bacd7805a
5 changed files with 172 additions and 12 deletions
Download Patch File Download Diff File Expand all files Collapse all files

57
samples/bpf/bpf_load.c
View File

@@ -16,6 +16,7 @@
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <poll.h>
#include <ctype.h>
#include "libbpf.h"
#include "bpf_helpers.h"
#include "bpf_load.h"
@@ -29,6 +30,19 @@ int map_fd[MAX_MAPS];
int prog_fd[MAX_PROGS];
int event_fd[MAX_PROGS];
int prog_cnt;
int prog_array_fd = -1;
static int populate_prog_array(const char *event, int prog_fd)
{
int ind = atoi(event), err;
err = bpf_update_elem(prog_array_fd, &ind, &prog_fd, BPF_ANY);
if (err < 0) {
printf("failed to store prog_fd in prog_array\n");
return -1;
}
return 0;
}
static int load_and_attach(const char *event, struct bpf_insn *prog, int size)
{
@@ -54,12 +68,40 @@ static int load_and_attach(const char *event, struct bpf_insn *prog, int size)
return -1;
}
fd = bpf_prog_load(prog_type, prog, size, license, kern_version);
if (fd < 0) {
printf("bpf_prog_load() err=%d\n%s", errno, bpf_log_buf);
return -1;
}
prog_fd[prog_cnt++] = fd;
if (is_socket) {
event += 6;
if (*event != '/')
return 0;
event++;
if (!isdigit(*event)) {
printf("invalid prog number\n");
return -1;
}
return populate_prog_array(event, fd);
}
if (is_kprobe || is_kretprobe) {
if (is_kprobe)
event += 7;
else
event += 10;
if (*event == 0) {
printf("event name cannot be empty\n");
return -1;
}
if (isdigit(*event))
return populate_prog_array(event, fd);
snprintf(buf, sizeof(buf),
"echo '%c:%s %s' >> /sys/kernel/debug/tracing/kprobe_events",
is_kprobe ? 'p' : 'r', event, event);
@@ -71,18 +113,6 @@ static int load_and_attach(const char *event, struct bpf_insn *prog, int size)
}
}
fd = bpf_prog_load(prog_type, prog, size, license, kern_version);
if (fd < 0) {
printf("bpf_prog_load() err=%d\n%s", errno, bpf_log_buf);
return -1;
}
prog_fd[prog_cnt++] = fd;
if (is_socket)
return 0;
strcpy(buf, DEBUGFS);
strcat(buf, "events/kprobes/");
strcat(buf, event);
@@ -130,6 +160,9 @@ static int load_maps(struct bpf_map_def *maps, int len)
maps[i].max_entries);
if (map_fd[i] < 0)
return 1;
if (maps[i].type == BPF_MAP_TYPE_PROG_ARRAY)
prog_array_fd = map_fd[i];
}
return 0;
}