Merge branch 'Ensure type tags are always ordered first in BTF'

Kumar Kartikeya Dwivedi says:

====================

When iterating over modifiers, ensure that type tags can only occur at head of
the chain, and don't occur later, such that checking for them once in the start
tells us there are no more type tags in later modifiers. Clang already ensures
to emit such BTF, but user can craft their own BTF which violates such
assumptions if relied upon in the kernel.

Changelog:
----------
v2 -> v3
v2: https://lore.kernel.org/bpf/20220418224719.1604889-1-memxor@gmail.com

 * Address nit from Yonghong, add Acked-by

v1 -> v2
v1: https://lore.kernel.org/bpf/20220406004121.282699-1-memxor@gmail.com

 * Fix for bug pointed out by Yonghong
 * Update selftests to include Yonghong's example
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 54 insertions, 0 deletions

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 0918a39279f6..7906b9bf7ff8 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -4541,6 +4541,48 @@ static int btf_parse_hdr(struct btf_verifier_env *env)
 	return 0;
 }
 
+static int btf_check_type_tags(struct btf_verifier_env *env,
+			       struct btf *btf, int start_id)
+{
+	int i, n, good_id = start_id - 1;
+	bool in_tags;
+
+	n = btf_nr_types(btf);
+	for (i = start_id; i < n; i++) {
+		const struct btf_type *t;
+		u32 cur_id = i;
+
+		t = btf_type_by_id(btf, i);
+		if (!t)
+			return -EINVAL;
+		if (!btf_type_is_modifier(t))
+			continue;
+
+		cond_resched();
+
+		in_tags = btf_type_is_type_tag(t);
+		while (btf_type_is_modifier(t)) {
+			if (btf_type_is_type_tag(t)) {
+				if (!in_tags) {
+					btf_verifier_log(env, "Type tags don't precede modifiers");
+					return -EINVAL;
+				}
+			} else if (in_tags) {
+				in_tags = false;
+			}
+			if (cur_id <= good_id)
+				break;
+			/* Move to next type */
+			cur_id = t->type;
+			t = btf_type_by_id(btf, cur_id);
+			if (!t)
+				return -EINVAL;
+		}
+		good_id = i;
+	}
+	return 0;
+}
+
 static struct btf *btf_parse(bpfptr_t btf_data, u32 btf_data_size,
 			     u32 log_level, char __user *log_ubuf, u32 log_size)
 {
@@ -4608,6 +4650,10 @@ static struct btf *btf_parse(bpfptr_t btf_data, u32 btf_data_size,
 	if (err)
 		goto errout;
 
+	err = btf_check_type_tags(env, btf, 1);
+	if (err)
+		goto errout;
+
 	if (log->level && bpf_verifier_log_full(log)) {
 		err = -ENOSPC;
 		goto errout;
@@ -4809,6 +4855,10 @@ struct btf *btf_parse_vmlinux(void)
 	if (err)
 		goto errout;
 
+	err = btf_check_type_tags(env, btf, 1);
+	if (err)
+		goto errout;
+
 	/* btf_parse_vmlinux() runs under bpf_verifier_lock */
 	bpf_ctx_convert.t = btf_type_by_id(btf, bpf_ctx_convert_btf_id[0]);
 
@@ -4894,6 +4944,10 @@ static struct btf *btf_parse_module(const char *module_name, const void *data, u
 	if (err)
 		goto errout;
 
+	err = btf_check_type_tags(env, btf, btf_nr_types(base_btf));
+	if (err)
+		goto errout;
+
 	btf_verifier_env_free(env);
 	refcount_set(&btf->refcnt, 1);
 	return btf;