Commit 4d56a76e authored May 24, 2018 by Sandipan Das Committed by Daniel Borkmann May 24, 2018

bpf: fix multi-function JITed dump obtained via syscall



Currently, for multi-function programs, we cannot get the JITed
instructions using the bpf system call's BPF_OBJ_GET_INFO_BY_FD
command. Because of this, userspace tools such as bpftool fail
to identify a multi-function program as being JITed or not.

With the JIT enabled and the test program running, this can be
verified as follows:

  # cat /proc/sys/net/core/bpf_jit_enable
  1

Before applying this patch:

  # bpftool prog list
  1: kprobe  name foo  tag b811aab41a39ad3d  gpl
          loaded_at 2018-05-16T11:43:38+0530  uid 0
          xlated 216B  not jited  memlock 65536B
  ...

  # bpftool prog dump jited id 1
  no instructions returned

After applying this patch:

  # bpftool prog list
  1: kprobe  name foo  tag b811aab41a39ad3d  gpl
          loaded_at 2018-05-16T12:13:01+0530  uid 0
          xlated 216B  jited 308B  memlock 65536B
  ...

  # bpftool prog dump jited id 1
     0:   nop
     4:   nop
     8:   mflr    r0
     c:   std     r0,16(r1)
    10:   stdu    r1,-112(r1)
    14:   std     r31,104(r1)
    18:   addi    r31,r1,48
    1c:   li      r3,10
  ...

Signed-off-by: Sandipan Das <sandipan@linux.vnet.ibm.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

parent f84192ee

kernel/bpf/syscall.c

+34 −3

Original line number	Diff line number	Diff line
		@@ -1970,13 +1970,44 @@ static int bpf_prog_get_info_by_fd(struct bpf_prog *prog,
		* for offload.
		*/
		ulen = info.jited_prog_len;
		if (prog->aux->func_cnt) {
		u32 i;

		info.jited_prog_len = 0;
		for (i = 0; i < prog->aux->func_cnt; i++)
		info.jited_prog_len += prog->aux->func[i]->jited_len;
		} else {
		info.jited_prog_len = prog->jited_len;
		}

		if (info.jited_prog_len && ulen) {
		if (bpf_dump_raw_ok()) {
		uinsns = u64_to_user_ptr(info.jited_prog_insns);
		ulen = min_t(u32, info.jited_prog_len, ulen);

		/* for multi-function programs, copy the JITed
		* instructions for all the functions
		*/
		if (prog->aux->func_cnt) {
		u32 len, free, i;
		u8 *img;

		free = ulen;
		for (i = 0; i < prog->aux->func_cnt; i++) {
		len = prog->aux->func[i]->jited_len;
		len = min_t(u32, len, free);
		img = (u8 *) prog->aux->func[i]->bpf_func;
		if (copy_to_user(uinsns, img, len))
		return -EFAULT;
		uinsns += len;
		free -= len;
		if (!free)
		break;
		}
		} else {
		if (copy_to_user(uinsns, prog->bpf_func, ulen))
		return -EFAULT;
		}
		} else {
		info.jited_prog_insns = 0;
		}

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