bpf: Process in-kernel BTF

If in-kernel BTF exists parse it and prepare 'struct btf *btf_vmlinux'
for further use by the verifier.
In-kernel BTF is trusted just like kallsyms and other build artifacts
embedded into vmlinux.
Yet run this BTF image through BTF verifier to make sure
that it is valid and it wasn't mangled during the build.
If in-kernel BTF is incorrect it means either gcc or pahole or kernel
are buggy. In such case disallow loading BPF programs.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20191016032505.2089704-4-ast@kernel.org

4 files changed, 94 insertions, 2 deletions

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 26a6d58ca78c..713efae62e96 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -330,10 +330,12 @@ static inline bool bpf_verifier_log_full(const struct bpf_verifier_log *log)
 #define BPF_LOG_STATS	4
 #define BPF_LOG_LEVEL	(BPF_LOG_LEVEL1 | BPF_LOG_LEVEL2)
 #define BPF_LOG_MASK	(BPF_LOG_LEVEL | BPF_LOG_STATS)
+#define BPF_LOG_KERNEL	(BPF_LOG_MASK + 1) /* kernel internal flag */
 
 static inline bool bpf_verifier_log_needed(const struct bpf_verifier_log *log)
 {
-	return log->level && log->ubuf && !bpf_verifier_log_full(log);
+	return (log->level && log->ubuf && !bpf_verifier_log_full(log)) ||
+		log->level == BPF_LOG_KERNEL;
 }
 
 #define BPF_MAX_SUBPROGS 256
diff --git a/include/linux/btf.h b/include/linux/btf.h
index 64cdf2a23d42..55d43bc856be 100644
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -56,6 +56,7 @@ bool btf_type_is_void(const struct btf_type *t);
 #ifdef CONFIG_BPF_SYSCALL
 const struct btf_type *btf_type_by_id(const struct btf *btf, u32 type_id);
 const char *btf_name_by_offset(const struct btf *btf, u32 offset);
+struct btf *btf_parse_vmlinux(void);
 #else
 static inline const struct btf_type *btf_type_by_id(const struct btf *btf,
 						    u32 type_id)
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 29c7c06c6bd6..ddeab1e8d21e 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -698,6 +698,13 @@ __printf(4, 5) static void __btf_verifier_log_type(struct btf_verifier_env *env,
 	if (!bpf_verifier_log_needed(log))
 		return;
 
+	/* btf verifier prints all types it is processing via
+	 * btf_verifier_log_type(..., fmt = NULL).
+	 * Skip those prints for in-kernel BTF verification.
+	 */
+	if (log->level == BPF_LOG_KERNEL && !fmt)
+		return;
+
 	__btf_verifier_log(log, "[%u] %s %s%s",
 			   env->log_type_id,
 			   btf_kind_str[kind],
@@ -735,6 +742,8 @@ static void btf_verifier_log_member(struct btf_verifier_env *env,
 	if (!bpf_verifier_log_needed(log))
 		return;
 
+	if (log->level == BPF_LOG_KERNEL && !fmt)
+		return;
 	/* The CHECK_META phase already did a btf dump.
 	 *
 	 * If member is logged again, it must hit an error in
@@ -777,6 +786,8 @@ static void btf_verifier_log_vsi(struct btf_verifier_env *env,
 
 	if (!bpf_verifier_log_needed(log))
 		return;
+	if (log->level == BPF_LOG_KERNEL && !fmt)
+		return;
 	if (env->phase != CHECK_META)
 		btf_verifier_log_type(env, datasec_type, NULL);
 
@@ -802,6 +813,8 @@ static void btf_verifier_log_hdr(struct btf_verifier_env *env,
 	if (!bpf_verifier_log_needed(log))
 		return;
 
+	if (log->level == BPF_LOG_KERNEL)
+		return;
 	hdr = &btf->hdr;
 	__btf_verifier_log(log, "magic: 0x%x\n", hdr->magic);
 	__btf_verifier_log(log, "version: %u\n", hdr->version);
@@ -2405,7 +2418,8 @@ static s32 btf_enum_check_meta(struct btf_verifier_env *env,
 			return -EINVAL;
 		}
 
-
+		if (env->log.level == BPF_LOG_KERNEL)
+			continue;
 		btf_verifier_log(env, "\t%s val=%d\n",
 				 __btf_name_by_offset(btf, enums[i].name_off),
 				 enums[i].val);
@@ -3367,6 +3381,61 @@ errout:
 	return ERR_PTR(err);
 }
 
+extern char __weak _binary__btf_vmlinux_bin_start[];
+extern char __weak _binary__btf_vmlinux_bin_end[];
+
+struct btf *btf_parse_vmlinux(void)
+{
+	struct btf_verifier_env *env = NULL;
+	struct bpf_verifier_log *log;
+	struct btf *btf = NULL;
+	int err;
+
+	env = kzalloc(sizeof(*env), GFP_KERNEL | __GFP_NOWARN);
+	if (!env)
+		return ERR_PTR(-ENOMEM);
+
+	log = &env->log;
+	log->level = BPF_LOG_KERNEL;
+
+	btf = kzalloc(sizeof(*btf), GFP_KERNEL | __GFP_NOWARN);
+	if (!btf) {
+		err = -ENOMEM;
+		goto errout;
+	}
+	env->btf = btf;
+
+	btf->data = _binary__btf_vmlinux_bin_start;
+	btf->data_size = _binary__btf_vmlinux_bin_end -
+		_binary__btf_vmlinux_bin_start;
+
+	err = btf_parse_hdr(env);
+	if (err)
+		goto errout;
+
+	btf->nohdr_data = btf->data + btf->hdr.hdr_len;
+
+	err = btf_parse_str_sec(env);
+	if (err)
+		goto errout;
+
+	err = btf_check_all_metas(env);
+	if (err)
+		goto errout;
+
+	btf_verifier_env_free(env);
+	refcount_set(&btf->refcnt, 1);
+	return btf;
+
+errout:
+	btf_verifier_env_free(env);
+	if (btf) {
+		kvfree(btf->types);
+		kfree(btf);
+	}
+	return ERR_PTR(err);
+}
+
 void btf_type_seq_show(const struct btf *btf, u32 type_id, void *obj,
 		       struct seq_file *m)
 {
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index d3446f018b9a..466b3b19de4d 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -207,6 +207,8 @@ struct bpf_call_arg_meta {
 	int func_id;
 };
 
+struct btf *btf_vmlinux;
+
 static DEFINE_MUTEX(bpf_verifier_lock);
 
 static const struct bpf_line_info *
@@ -243,6 +245,10 @@ void bpf_verifier_vlog(struct bpf_verifier_log *log, const char *fmt,
 	n = min(log->len_total - log->len_used - 1, n);
 	log->kbuf[n] = '\0';
 
+	if (log->level == BPF_LOG_KERNEL) {
+		pr_err("BPF:%s\n", log->kbuf);
+		return;
+	}
 	if (!copy_to_user(log->ubuf + log->len_used, log->kbuf, n + 1))
 		log->len_used += n;
 	else
@@ -9294,6 +9300,13 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr,
 	env->ops = bpf_verifier_ops[env->prog->type];
 	is_priv = capable(CAP_SYS_ADMIN);
 
+	if (!btf_vmlinux && IS_ENABLED(CONFIG_DEBUG_INFO_BTF)) {
+		mutex_lock(&bpf_verifier_lock);
+		if (!btf_vmlinux)
+			btf_vmlinux = btf_parse_vmlinux();
+		mutex_unlock(&bpf_verifier_lock);
+	}
+
 	/* grab the mutex to protect few globals used by verifier */
 	if (!is_priv)
 		mutex_lock(&bpf_verifier_lock);
@@ -9313,6 +9326,13 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr,
 			goto err_unlock;
 	}
 
+	if (IS_ERR(btf_vmlinux)) {
+		/* Either gcc or pahole or kernel are broken. */
+		verbose(env, "in-kernel BTF is malformed\n");
+		ret = PTR_ERR(btf_vmlinux);
+		goto err_unlock;
+	}
+
 	env->strict_alignment = !!(attr->prog_flags & BPF_F_STRICT_ALIGNMENT);
 	if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS))
 		env->strict_alignment = true;