[PATCH v2 bpf-next 3/3] bpf: add faked "ending" subprog
From: Jiong Wang <hidden>
Date: 2018-05-02 20:17:33
Subsystem:
bpf [core], bpf [general] (safe dynamic programs and tools), the rest · Maintainers:
Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman, Kumar Kartikeya Dwivedi, Linus Torvalds
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 <redacted>
---
kernel/bpf/verifier.c | 34 ++++++++++++++--------------------
1 file changed, 14 insertions(+), 20 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 9764b9b..65a6e2e 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c@@ -766,7 +766,7 @@ 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; }
@@ -807,16 +807,18 @@ 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;
@@ -840,11 +842,9 @@ static int check_subprogs(struct bpf_verifier_env *env) 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; } }
@@ -1499,7 +1499,6 @@ 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];
@@ -1514,10 +1513,7 @@ static int check_max_stack_depth(struct bpf_verifier_env *env) 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;
@@ -5070,7 +5066,8 @@ 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;
@@ -5268,10 +5265,7 @@ 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);
--
2.7.4