Subject: [PATCH net-next 3/9] bpf: teach verifier to track stack depth

From: Alexei Starovoitov <[email-masked]>
Date: Tue, 30 May 2017 13:31:29 -0700

teach verifier to track bpf program stack depth

Signed-off-by: Alexei Starovoitov <[email-masked]>
Acked-by: Daniel Borkmann <[email-masked]>
---
 include/linux/bpf.h   |  1 +
 kernel/bpf/verifier.c | 10 +++++++++-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 6bb38d76faf4..fcc80ca11045 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -171,6 +171,7 @@ struct bpf_prog_aux {
 	atomic_t refcnt;
 	u32 used_map_cnt;
 	u32 max_ctx_offset;
+	u32 stack_depth;
 	struct latch_tree_node ksym_tnode;
 	struct list_head ksym_lnode;
 	const struct bpf_verifier_ops *ops;
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 28113d0e8e92..d96f27ff9f6f 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -926,6 +926,10 @@ static int check_mem_access(struct bpf_verifier_env *env, u32 regno, int off,
 			verbose("invalid stack off=%d size=%d\n", off, size);
 			return -EACCES;
 		}
+
+		if (env->prog->aux->stack_depth < -off)
+			env->prog->aux->stack_depth = -off;
+
 		if (t == BPF_WRITE) {
 			if (!env->allow_ptr_leaks &&
 			    state->stack_slot_type[MAX_BPF_STACK + off] == STACK_SPILL &&
@@ -1032,6 +1036,9 @@ static int check_stack_boundary(struct bpf_verifier_env *env, int regno,
 		return -EACCES;
 	}
 
+	if (env->prog->aux->stack_depth < -off)
+		env->prog->aux->stack_depth = -off;
+
 	if (meta && meta->raw_mode) {
 		meta->access_size = access_size;
 		meta->regno = regno;
@@ -3167,7 +3174,8 @@ static int do_check(struct bpf_verifier_env *env)
 		insn_idx++;
 	}
 
-	verbose("processed %d insns\n", insn_processed);
+	verbose("processed %d insns, stack depth %d\n",
+		insn_processed, env->prog->aux->stack_depth);
 	return 0;
 }
 
-- 
2.9.3