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>

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 068a4fc..c8e987a 100644 (file)
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -1970,13 +1970,44 @@ static int bpf_prog_get_info_by_fd(struct bpf_prog *prog,
         * for offload.
         */
        ulen = info.jited_prog_len;
-       info.jited_prog_len = prog->jited_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);
-                       if (copy_to_user(uinsns, prog->bpf_func, ulen))
-                               return -EFAULT;
+
+                       /* 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;
                }