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>

1 files changed, 34 insertions, 3 deletions

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 068a4fc79ddb..c8e987a612b5 100644
--- 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;
                 }