bpf: add faked "ending" subprog

There are quite a few code snippet like the following in verifier:

       subprog_start = 0;
       if (env->subprog_cnt == cur_subprog + 1)
               subprog_end = insn_cnt;
       else
               subprog_end = env->subprog_info[cur_subprog + 1].start;

The reason is there is no marker in subprog_info array to tell the end of
it.

We could resolve this issue by introducing a faked "ending" subprog.
The special "ending" subprog is with "insn_cnt" as start offset, so it is
serving as the end mark whenever we iterate over all subprogs.

Signed-off-by: Jiong Wang <jiong.wang@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 5b293b4abb70d1837b65f01d759fa09e42f97e8a..37e0affa515e8deff35c3f51e66ecaaa76661c94 100644 (file)
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -769,7 +769,7 @@ static int add_subprog(struct bpf_verifier_env *env, int off)
        ret = find_subprog(env, off);
        if (ret >= 0)
                return 0;
-       if (env->subprog_cnt > BPF_MAX_SUBPROGS) {
+       if (env->subprog_cnt >= BPF_MAX_SUBPROGS) {
                verbose(env, "too many subprograms\n");
                return -E2BIG;
        }
@@ -810,16 +810,18 @@ static int check_subprogs(struct bpf_verifier_env *env)
                        return ret;
        }
 
+       /* Add a fake 'exit' subprog which could simplify subprog iteration
+        * logic. 'subprog_cnt' should not be increased.
+        */
+       subprog[env->subprog_cnt].start = insn_cnt;
+
        if (env->log.level > 1)
                for (i = 0; i < env->subprog_cnt; i++)
                        verbose(env, "func#%d @%d\n", i, subprog[i].start);
 
        /* now check that all jumps are within the same subprog */
-       subprog_start = 0;
-       if (env->subprog_cnt == cur_subprog + 1)
-               subprog_end = insn_cnt;
-       else
-               subprog_end = subprog[cur_subprog + 1].start;
+       subprog_start = subprog[cur_subprog].start;
+       subprog_end = subprog[cur_subprog + 1].start;
        for (i = 0; i < insn_cnt; i++) {
                u8 code = insn[i].code;
 
@@ -843,11 +845,9 @@ next:
                                verbose(env, "last insn is not an exit or jmp\n");
                                return -EINVAL;
                        }
-                       cur_subprog++;
                        subprog_start = subprog_end;
-                       if (env->subprog_cnt == cur_subprog + 1)
-                               subprog_end = insn_cnt;
-                       else
+                       cur_subprog++;
+                       if (cur_subprog < env->subprog_cnt)
                                subprog_end = subprog[cur_subprog + 1].start;
                }
        }
@@ -1502,7 +1502,6 @@ static int check_max_stack_depth(struct bpf_verifier_env *env)
        int depth = 0, frame = 0, idx = 0, i = 0, subprog_end;
        struct bpf_subprog_info *subprog = env->subprog_info;
        struct bpf_insn *insn = env->prog->insnsi;
-       int insn_cnt = env->prog->len;
        int ret_insn[MAX_CALL_FRAMES];
        int ret_prog[MAX_CALL_FRAMES];
 
@@ -1517,10 +1516,7 @@ process_func:
                return -EACCES;
        }
 continue_func:
-       if (env->subprog_cnt == idx + 1)
-               subprog_end = insn_cnt;
-       else
-               subprog_end = subprog[idx + 1].start;
+       subprog_end = subprog[idx + 1].start;
        for (; i < subprog_end; i++) {
                if (insn[i].code != (BPF_JMP | BPF_CALL))
                        continue;
@@ -5141,7 +5137,8 @@ static void adjust_subprog_starts(struct bpf_verifier_env *env, u32 off, u32 len
 
        if (len == 1)
                return;
-       for (i = 0; i < env->subprog_cnt; i++) {
+       /* NOTE: fake 'exit' subprog should be updated as well. */
+       for (i = 0; i <= env->subprog_cnt; i++) {
                if (env->subprog_info[i].start < off)
                        continue;
                env->subprog_info[i].start += len - 1;
@@ -5339,10 +5336,7 @@ static int jit_subprogs(struct bpf_verifier_env *env)
 
        for (i = 0; i < env->subprog_cnt; i++) {
                subprog_start = subprog_end;
-               if (env->subprog_cnt == i + 1)
-                       subprog_end = prog->len;
-               else
-                       subprog_end = env->subprog_info[i + 1].start;
+               subprog_end = env->subprog_info[i + 1].start;
 
                len = subprog_end - subprog_start;
                func[i] = bpf_prog_alloc(bpf_prog_size(len), GFP_USER);