bpf: Introduce bpf_func_info

This patch added interface to load a program with the following
additional information:
   . prog_btf_fd
   . func_info, func_info_rec_size and func_info_cnt
where func_info will provide function range and type_id
corresponding to each function.

The func_info_rec_size is introduced in the UAPI to specify
struct bpf_func_info size passed from user space. This
intends to make bpf_func_info structure growable in the future.
If the kernel gets a different bpf_func_info size from userspace,
it will try to handle user request with part of bpf_func_info
it can understand. In this patch, kernel can understand
  struct bpf_func_info {
       __u32   insn_offset;
       __u32   type_id;
  };
If user passed a bpf func_info record size of 16 bytes, the
kernel can still handle part of records with the above definition.

If verifier agrees with function range provided by the user,
the bpf_prog ksym for each function will use the func name
provided in the type_id, which is supposed to provide better
encoding as it is not limited by 16 bytes program name
limitation and this is better for bpf program which contains
multiple subprograms.

The bpf_prog_info interface is also extended to
return btf_id, func_info, func_info_rec_size and func_info_cnt
to userspace, so userspace can print out the function prototype
for each xlated function. The insn_offset in the returned
func_info corresponds to the insn offset for xlated functions.
With other jit related fields in bpf_prog_info, userspace can also
print out function prototypes for each jited function.

Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 55 insertions, 4 deletions

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index cf5040fd5434..998377808102 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -1213,6 +1213,7 @@ static void __bpf_prog_put(struct bpf_prog *prog, bool do_idr_lock)
                 /* bpf_prog_free_id() must be called first */
                 bpf_prog_free_id(prog, do_idr_lock);
                 bpf_prog_kallsyms_del_all(prog);
+                btf_put(prog->aux->btf);
 
                 call_rcu(&prog->aux->rcu, __bpf_prog_put_rcu);
         }
@@ -1437,9 +1438,9 @@ bpf_prog_load_check_attach_type(enum bpf_prog_type prog_type,
 }
 
 /* last field in 'union bpf_attr' used by this command */
-#define BPF_PROG_LOAD_LAST_FIELD expected_attach_type
+#define BPF_PROG_LOAD_LAST_FIELD func_info_cnt
 
-static int bpf_prog_load(union bpf_attr *attr)
+static int bpf_prog_load(union bpf_attr *attr, union bpf_attr __user *uattr)
 {
         enum bpf_prog_type type = attr->prog_type;
         struct bpf_prog *prog;
@@ -1525,7 +1526,7 @@ static int bpf_prog_load(union bpf_attr *attr)
                 goto free_prog;
 
         /* run eBPF verifier */
-        err = bpf_check(&prog, attr);
+        err = bpf_check(&prog, attr, uattr);
         if (err < 0)
                 goto free_used_maps;
 
@@ -2079,6 +2080,7 @@ static int bpf_prog_get_info_by_fd(struct bpf_prog *prog,
                 info.xlated_prog_len = 0;
                 info.nr_jited_ksyms = 0;
                 info.nr_jited_func_lens = 0;
+                info.func_info_cnt = 0;
                 goto done;
         }
 
@@ -2216,6 +2218,55 @@ static int bpf_prog_get_info_by_fd(struct bpf_prog *prog,
                 }
         }
 
+        if (prog->aux->btf) {
+                u32 ucnt, urec_size;
+
+                info.btf_id = btf_id(prog->aux->btf);
+
+                ucnt = info.func_info_cnt;
+                info.func_info_cnt = prog->aux->func_cnt ? : 1;
+                urec_size = info.func_info_rec_size;
+                info.func_info_rec_size = sizeof(struct bpf_func_info);
+                if (ucnt) {
+                        /* expect passed-in urec_size is what the kernel expects */
+                        if (urec_size != info.func_info_rec_size)
+                                return -EINVAL;
+
+                        if (bpf_dump_raw_ok()) {
+                                struct bpf_func_info kern_finfo;
+                                char __user *user_finfo;
+                                u32 i, insn_offset;
+
+                                user_finfo = u64_to_user_ptr(info.func_info);
+                                if (prog->aux->func_cnt) {
+                                        ucnt = min_t(u32, info.func_info_cnt, ucnt);
+                                        insn_offset = 0;
+                                        for (i = 0; i < ucnt; i++) {
+                                                kern_finfo.insn_offset = insn_offset;
+                                                kern_finfo.type_id = prog->aux->func[i]->aux->type_id;
+                                                if (copy_to_user(user_finfo, &kern_finfo,
+                                                                 sizeof(kern_finfo)))
+                                                        return -EFAULT;
+
+                                                /* func[i]->len holds the prog len */
+                                                insn_offset += prog->aux->func[i]->len;
+                                                user_finfo += urec_size;
+                                        }
+                                } else {
+                                        kern_finfo.insn_offset = 0;
+                                        kern_finfo.type_id = prog->aux->type_id;
+                                        if (copy_to_user(user_finfo, &kern_finfo,
+                                                         sizeof(kern_finfo)))
+                                                return -EFAULT;
+                                }
+                        } else {
+                                info.func_info_cnt = 0;
+                        }
+                }
+        } else {
+                info.func_info_cnt = 0;
+        }
+
 done:
         if (copy_to_user(uinfo, &info, info_len) ||
             put_user(info_len, &uattr->info.info_len))
@@ -2501,7 +2552,7 @@ SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, siz
                 err = map_get_next_key(&attr);
                 break;
         case BPF_PROG_LOAD:
-                err = bpf_prog_load(&attr);
+                err = bpf_prog_load(&attr, uattr);
                 break;
         case BPF_OBJ_PIN:
                 err = bpf_obj_pin(&attr);