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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>
This commit is contained in:
Jiong Wang 2018-05-02 16:17:19 -04:00 committed by Daniel Borkmann
parent 9c8105bd44
commit 4cb3d99c84
1 changed files with 14 additions and 20 deletions
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28
kernel/bpf/verifier.c
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@ -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;
}
@ -810,15 +810,17 @@ 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_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];
@ -1517,9 +1516,6 @@ process_func:
return -EACCES;
}
continue_func:
if (env->subprog_cnt == idx + 1)
subprog_end = insn_cnt;
else
subprog_end = subprog[idx + 1].start;
for (; i < subprog_end; i++) {
if (insn[i].code != (BPF_JMP | BPF_CALL))
@ -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;
@ -5339,9 +5336,6 @@ 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;
len = subprog_end - subprog_start;