bpf: Introduce bpf_func_info

This patch added interface to load a program with the following
additional information:
   . prog_btf_fd
   . func_info, func_info_rec_size and func_info_cnt
where func_info will provide function range and type_id
corresponding to each function.

The func_info_rec_size is introduced in the UAPI to specify
struct bpf_func_info size passed from user space. This
intends to make bpf_func_info structure growable in the future.
If the kernel gets a different bpf_func_info size from userspace,
it will try to handle user request with part of bpf_func_info
it can understand. In this patch, kernel can understand
  struct bpf_func_info {
       __u32   insn_offset;
       __u32   type_id;
  };
If user passed a bpf func_info record size of 16 bytes, the
kernel can still handle part of records with the above definition.

If verifier agrees with function range provided by the user,
the bpf_prog ksym for each function will use the func name
provided in the type_id, which is supposed to provide better
encoding as it is not limited by 16 bytes program name
limitation and this is better for bpf program which contains
multiple subprograms.

The bpf_prog_info interface is also extended to
return btf_id, func_info, func_info_rec_size and func_info_cnt
to userspace, so userspace can print out the function prototype
for each xlated function. The insn_offset in the returned
func_info corresponds to the insn offset for xlated functions.
With other jit related fields in bpf_prog_info, userspace can also
print out function prototypes for each jited function.

Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

4 files changed, 189 insertions, 7 deletions

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 6a2be79b73fc..69da9169819a 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -474,7 +474,7 @@ static bool btf_name_valid_identifier(const struct btf *btf, u32 offset)
 	return !*src;
 }
 
-static const char *btf_name_by_offset(const struct btf *btf, u32 offset)
+const char *btf_name_by_offset(const struct btf *btf, u32 offset)
 {
 	if (!offset)
 		return "(anon)";
@@ -484,7 +484,7 @@ static const char *btf_name_by_offset(const struct btf *btf, u32 offset)
 		return "(invalid-name-offset)";
 }
 
-static const struct btf_type *btf_type_by_id(const struct btf *btf, u32 type_id)
+const struct btf_type *btf_type_by_id(const struct btf *btf, u32 type_id)
 {
 	if (type_id > btf->nr_types)
 		return NULL;
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 1a796e0799ec..16d77012ad3e 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -21,12 +21,14 @@
  * Kris Katterjohn - Added many additional checks in bpf_check_classic()
  */
 
+#include <uapi/linux/btf.h>
 #include <linux/filter.h>
 #include <linux/skbuff.h>
 #include <linux/vmalloc.h>
 #include <linux/random.h>
 #include <linux/moduleloader.h>
 #include <linux/bpf.h>
+#include <linux/btf.h>
 #include <linux/frame.h>
 #include <linux/rbtree_latch.h>
 #include <linux/kallsyms.h>
@@ -390,6 +392,8 @@ bpf_get_prog_addr_region(const struct bpf_prog *prog,
 static void bpf_get_prog_name(const struct bpf_prog *prog, char *sym)
 {
 	const char *end = sym + KSYM_NAME_LEN;
+	const struct btf_type *type;
+	const char *func_name;
 
 	BUILD_BUG_ON(sizeof("bpf_prog_") +
 		     sizeof(prog->tag) * 2 +
@@ -404,6 +408,15 @@ static void bpf_get_prog_name(const struct bpf_prog *prog, char *sym)
 
 	sym += snprintf(sym, KSYM_NAME_LEN, "bpf_prog_");
 	sym  = bin2hex(sym, prog->tag, sizeof(prog->tag));
+
+	/* prog->aux->name will be ignored if full btf name is available */
+	if (prog->aux->btf) {
+		type = btf_type_by_id(prog->aux->btf, prog->aux->type_id);
+		func_name = btf_name_by_offset(prog->aux->btf, type->name_off);
+		snprintf(sym, (size_t)(end - sym), "_%s", func_name);
+		return;
+	}
+
 	if (prog->aux->name[0])
 		snprintf(sym, (size_t)(end - sym), "_%s", prog->aux->name);
 	else
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index cf5040fd5434..998377808102 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -1213,6 +1213,7 @@ static void __bpf_prog_put(struct bpf_prog *prog, bool do_idr_lock)
 		/* bpf_prog_free_id() must be called first */
 		bpf_prog_free_id(prog, do_idr_lock);
 		bpf_prog_kallsyms_del_all(prog);
+		btf_put(prog->aux->btf);
 
 		call_rcu(&prog->aux->rcu, __bpf_prog_put_rcu);
 	}
@@ -1437,9 +1438,9 @@ bpf_prog_load_check_attach_type(enum bpf_prog_type prog_type,
 }
 
 /* last field in 'union bpf_attr' used by this command */
-#define	BPF_PROG_LOAD_LAST_FIELD expected_attach_type
+#define	BPF_PROG_LOAD_LAST_FIELD func_info_cnt
 
-static int bpf_prog_load(union bpf_attr *attr)
+static int bpf_prog_load(union bpf_attr *attr, union bpf_attr __user *uattr)
 {
 	enum bpf_prog_type type = attr->prog_type;
 	struct bpf_prog *prog;
@@ -1525,7 +1526,7 @@ static int bpf_prog_load(union bpf_attr *attr)
 		goto free_prog;
 
 	/* run eBPF verifier */
-	err = bpf_check(&prog, attr);
+	err = bpf_check(&prog, attr, uattr);
 	if (err < 0)
 		goto free_used_maps;
 
@@ -2079,6 +2080,7 @@ static int bpf_prog_get_info_by_fd(struct bpf_prog *prog,
 		info.xlated_prog_len = 0;
 		info.nr_jited_ksyms = 0;
 		info.nr_jited_func_lens = 0;
+		info.func_info_cnt = 0;
 		goto done;
 	}
 
@@ -2216,6 +2218,55 @@ static int bpf_prog_get_info_by_fd(struct bpf_prog *prog,
 		}
 	}
 
+	if (prog->aux->btf) {
+		u32 ucnt, urec_size;
+
+		info.btf_id = btf_id(prog->aux->btf);
+
+		ucnt = info.func_info_cnt;
+		info.func_info_cnt = prog->aux->func_cnt ? : 1;
+		urec_size = info.func_info_rec_size;
+		info.func_info_rec_size = sizeof(struct bpf_func_info);
+		if (ucnt) {
+			/* expect passed-in urec_size is what the kernel expects */
+			if (urec_size != info.func_info_rec_size)
+				return -EINVAL;
+
+			if (bpf_dump_raw_ok()) {
+				struct bpf_func_info kern_finfo;
+				char __user *user_finfo;
+				u32 i, insn_offset;
+
+				user_finfo = u64_to_user_ptr(info.func_info);
+				if (prog->aux->func_cnt) {
+					ucnt = min_t(u32, info.func_info_cnt, ucnt);
+					insn_offset = 0;
+					for (i = 0; i < ucnt; i++) {
+						kern_finfo.insn_offset = insn_offset;
+						kern_finfo.type_id = prog->aux->func[i]->aux->type_id;
+						if (copy_to_user(user_finfo, &kern_finfo,
+								 sizeof(kern_finfo)))
+							return -EFAULT;
+
+						/* func[i]->len holds the prog len */
+						insn_offset += prog->aux->func[i]->len;
+						user_finfo += urec_size;
+					}
+				} else {
+					kern_finfo.insn_offset = 0;
+					kern_finfo.type_id = prog->aux->type_id;
+					if (copy_to_user(user_finfo, &kern_finfo,
+							 sizeof(kern_finfo)))
+						return -EFAULT;
+				}
+			} else {
+				info.func_info_cnt = 0;
+			}
+		}
+	} else {
+		info.func_info_cnt = 0;
+	}
+
 done:
 	if (copy_to_user(uinfo, &info, info_len) ||
 	    put_user(info_len, &uattr->info.info_len))
@@ -2501,7 +2552,7 @@ SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, siz
 		err = map_get_next_key(&attr);
 		break;
 	case BPF_PROG_LOAD:
-		err = bpf_prog_load(&attr);
+		err = bpf_prog_load(&attr, uattr);
 		break;
 	case BPF_OBJ_PIN:
 		err = bpf_obj_pin(&attr);
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index b5222aa61d54..f102c4fd0c5a 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -11,10 +11,12 @@
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  * General Public License for more details.
  */
+#include <uapi/linux/btf.h>
 #include <linux/kernel.h>
 #include <linux/types.h>
 #include <linux/slab.h>
 #include <linux/bpf.h>
+#include <linux/btf.h>
 #include <linux/bpf_verifier.h>
 #include <linux/filter.h>
 #include <net/netlink.h>
@@ -4639,6 +4641,114 @@ err_free:
 	return ret;
 }
 
+/* The minimum supported BTF func info size */
+#define MIN_BPF_FUNCINFO_SIZE	8
+#define MAX_FUNCINFO_REC_SIZE	252
+
+static int check_btf_func(struct bpf_prog *prog, struct bpf_verifier_env *env,
+			  union bpf_attr *attr, union bpf_attr __user *uattr)
+{
+	u32 i, nfuncs, urec_size, min_size, prev_offset;
+	u32 krec_size = sizeof(struct bpf_func_info);
+	struct bpf_func_info krecord = {};
+	const struct btf_type *type;
+	void __user *urecord;
+	struct btf *btf;
+	int ret = 0;
+
+	nfuncs = attr->func_info_cnt;
+	if (!nfuncs)
+		return 0;
+
+	if (nfuncs != env->subprog_cnt) {
+		verbose(env, "number of funcs in func_info doesn't match number of subprogs\n");
+		return -EINVAL;
+	}
+
+	urec_size = attr->func_info_rec_size;
+	if (urec_size < MIN_BPF_FUNCINFO_SIZE ||
+	    urec_size > MAX_FUNCINFO_REC_SIZE ||
+	    urec_size % sizeof(u32)) {
+		verbose(env, "invalid func info rec size %u\n", urec_size);
+		return -EINVAL;
+	}
+
+	btf = btf_get_by_fd(attr->prog_btf_fd);
+	if (IS_ERR(btf)) {
+		verbose(env, "unable to get btf from fd\n");
+		return PTR_ERR(btf);
+	}
+
+	urecord = u64_to_user_ptr(attr->func_info);
+	min_size = min_t(u32, krec_size, urec_size);
+
+	for (i = 0; i < nfuncs; i++) {
+		ret = bpf_check_uarg_tail_zero(urecord, krec_size, urec_size);
+		if (ret) {
+			if (ret == -E2BIG) {
+				verbose(env, "nonzero tailing record in func info");
+				/* set the size kernel expects so loader can zero
+				 * out the rest of the record.
+				 */
+				if (put_user(min_size, &uattr->func_info_rec_size))
+					ret = -EFAULT;
+			}
+			goto free_btf;
+		}
+
+		if (copy_from_user(&krecord, urecord, min_size)) {
+			ret = -EFAULT;
+			goto free_btf;
+		}
+
+		/* check insn_offset */
+		if (i == 0) {
+			if (krecord.insn_offset) {
+				verbose(env,
+					"nonzero insn_offset %u for the first func info record",
+					krecord.insn_offset);
+				ret = -EINVAL;
+				goto free_btf;
+			}
+		} else if (krecord.insn_offset <= prev_offset) {
+			verbose(env,
+				"same or smaller insn offset (%u) than previous func info record (%u)",
+				krecord.insn_offset, prev_offset);
+			ret = -EINVAL;
+			goto free_btf;
+		}
+
+		if (env->subprog_info[i].start != krecord.insn_offset) {
+			verbose(env, "func_info BTF section doesn't match subprog layout in BPF program\n");
+			ret = -EINVAL;
+			goto free_btf;
+		}
+
+		/* check type_id */
+		type = btf_type_by_id(btf, krecord.type_id);
+		if (!type || BTF_INFO_KIND(type->info) != BTF_KIND_FUNC) {
+			verbose(env, "invalid type id %d in func info",
+				krecord.type_id);
+			ret = -EINVAL;
+			goto free_btf;
+		}
+
+		if (i == 0)
+			prog->aux->type_id = krecord.type_id;
+		env->subprog_info[i].type_id = krecord.type_id;
+
+		prev_offset = krecord.insn_offset;
+		urecord += urec_size;
+	}
+
+	prog->aux->btf = btf;
+	return 0;
+
+free_btf:
+	btf_put(btf);
+	return ret;
+}
+
 /* check %cur's range satisfies %old's */
 static bool range_within(struct bpf_reg_state *old,
 			 struct bpf_reg_state *cur)
@@ -5939,6 +6049,9 @@ static int jit_subprogs(struct bpf_verifier_env *env)
 		func[i]->aux->name[0] = 'F';
 		func[i]->aux->stack_depth = env->subprog_info[i].stack_depth;
 		func[i]->jit_requested = 1;
+		/* the btf will be freed only at prog->aux */
+		func[i]->aux->btf = prog->aux->btf;
+		func[i]->aux->type_id = env->subprog_info[i].type_id;
 		func[i] = bpf_int_jit_compile(func[i]);
 		if (!func[i]->jited) {
 			err = -ENOTSUPP;
@@ -6325,7 +6438,8 @@ static void free_states(struct bpf_verifier_env *env)
 	kfree(env->explored_states);
 }
 
-int bpf_check(struct bpf_prog **prog, union bpf_attr *attr)
+int bpf_check(struct bpf_prog **prog, union bpf_attr *attr,
+	      union bpf_attr __user *uattr)
 {
 	struct bpf_verifier_env *env;
 	struct bpf_verifier_log *log;
@@ -6397,6 +6511,10 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr)
 	if (ret < 0)
 		goto skip_full_check;
 
+	ret = check_btf_func(env->prog, env, attr, uattr);
+	if (ret < 0)
+		goto skip_full_check;
+
 	ret = do_check(env);
 	if (env->cur_state) {
 		free_verifier_state(env->cur_state, true);