bpf: implement BPF_PROG_QUERY for BPF_LSM_CGROUP

We have two options:
1. Treat all BPF_LSM_CGROUP the same, regardless of attach_btf_id
2. Treat BPF_LSM_CGROUP+attach_btf_id as a separate hook point

I was doing (2) in the original patch, but switching to (1) here:

* bpf_prog_query returns all attached BPF_LSM_CGROUP programs
regardless of attach_btf_id
* attach_btf_id is exported via bpf_prog_info
Reviewed-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Link: https://lore.kernel.org/r/20220628174314.1216643-6-sdf@google.comSigned-off-by: Alexei Starovoitov <ast@kernel.org>

include/uapi/linux/bpf.h

@@ -1432,6 +1432,7 @@ union bpf_attr {
 		__u32		attach_flags;
 		__aligned_u64	prog_ids;
 		__u32		prog_cnt;
+		__aligned_u64	prog_attach_flags; /* output: per-program attach_flags */
 	} query;
 
 	struct { /* anonymous struct used by BPF_RAW_TRACEPOINT_OPEN command */
@@ -6076,6 +6077,8 @@ struct bpf_prog_info {
 	__u64 run_cnt;
 	__u64 recursion_misses;
 	__u32 verified_insns;
+	__u32 attach_btf_obj_id;
+	__u32 attach_btf_id;
 } __attribute__((aligned(8)));
 
 struct bpf_map_info {

kernel/bpf/cgroup.c

@@ -1017,57 +1017,90 @@ static int cgroup_bpf_detach(struct cgroup *cgrp, struct bpf_prog *prog,
 static int __cgroup_bpf_query(struct cgroup *cgrp, const union bpf_attr *attr,
 			      union bpf_attr __user *uattr)
 {
+	__u32 __user *prog_attach_flags = u64_to_user_ptr(attr->query.prog_attach_flags);
 	__u32 __user *prog_ids = u64_to_user_ptr(attr->query.prog_ids);
 	enum bpf_attach_type type = attr->query.attach_type;
+	enum cgroup_bpf_attach_type from_atype, to_atype;
 	enum cgroup_bpf_attach_type atype;
 	struct bpf_prog_array *effective;
-	struct hlist_head *progs;
-	struct bpf_prog *prog;
 	int cnt, ret = 0, i;
+	int total_cnt = 0;
 	u32 flags;
 
-	atype = to_cgroup_bpf_attach_type(type);
-	if (atype < 0)
-		return -EINVAL;
-
-	progs = &cgrp->bpf.progs[atype];
-	flags = cgrp->bpf.flags[atype];
+	if (type == BPF_LSM_CGROUP) {
+		if (attr->query.prog_cnt && prog_ids && !prog_attach_flags)
+			return -EINVAL;
 
-	effective = rcu_dereference_protected(cgrp->bpf.effective[atype],
-					      lockdep_is_held(&cgroup_mutex));
+		from_atype = CGROUP_LSM_START;
+		to_atype = CGROUP_LSM_END;
+		flags = 0;
+	} else {
+		from_atype = to_cgroup_bpf_attach_type(type);
+		if (from_atype < 0)
+			return -EINVAL;
+		to_atype = from_atype;
+		flags = cgrp->bpf.flags[from_atype];
+	}
 
-	if (attr->query.query_flags & BPF_F_QUERY_EFFECTIVE)
-		cnt = bpf_prog_array_length(effective);
-	else
-		cnt = prog_list_length(progs);
+	for (atype = from_atype; atype <= to_atype; atype++) {
+		if (attr->query.query_flags & BPF_F_QUERY_EFFECTIVE) {
+			effective = rcu_dereference_protected(cgrp->bpf.effective[atype],
+							      lockdep_is_held(&cgroup_mutex));
+			total_cnt += bpf_prog_array_length(effective);
+		} else {
+			total_cnt += prog_list_length(&cgrp->bpf.progs[atype]);
+		}
+	}
 
 	if (copy_to_user(&uattr->query.attach_flags, &flags, sizeof(flags)))
 		return -EFAULT;
-	if (copy_to_user(&uattr->query.prog_cnt, &cnt, sizeof(cnt)))
+	if (copy_to_user(&uattr->query.prog_cnt, &total_cnt, sizeof(total_cnt)))
 		return -EFAULT;
-	if (attr->query.prog_cnt == 0 || !prog_ids || !cnt)
+	if (attr->query.prog_cnt == 0 || !prog_ids || !total_cnt)
 		/* return early if user requested only program count + flags */
 		return 0;
-	if (attr->query.prog_cnt < cnt) {
-		cnt = attr->query.prog_cnt;
+
+	if (attr->query.prog_cnt < total_cnt) {
+		total_cnt = attr->query.prog_cnt;
 		ret = -ENOSPC;
 	}
 
-	if (attr->query.query_flags & BPF_F_QUERY_EFFECTIVE) {
-		return bpf_prog_array_copy_to_user(effective, prog_ids, cnt);
-	} else {
-		struct bpf_prog_list *pl;
-		u32 id;
+	for (atype = from_atype; atype <= to_atype && total_cnt; atype++) {
+		if (attr->query.query_flags & BPF_F_QUERY_EFFECTIVE) {
+			effective = rcu_dereference_protected(cgrp->bpf.effective[atype],
+							      lockdep_is_held(&cgroup_mutex));
+			cnt = min_t(int, bpf_prog_array_length(effective), total_cnt);
+			ret = bpf_prog_array_copy_to_user(effective, prog_ids, cnt);
+		} else {
+			struct hlist_head *progs;
+			struct bpf_prog_list *pl;
+			struct bpf_prog *prog;
+			u32 id;
+
+			progs = &cgrp->bpf.progs[atype];
+			cnt = min_t(int, prog_list_length(progs), total_cnt);
+			i = 0;
+			hlist_for_each_entry(pl, progs, node) {
+				prog = prog_list_prog(pl);
+				id = prog->aux->id;
+				if (copy_to_user(prog_ids + i, &id, sizeof(id)))
+					return -EFAULT;
+				if (++i == cnt)
+					break;
+			}
+		}
 
-		i = 0;
-		hlist_for_each_entry(pl, progs, node) {
-			prog = prog_list_prog(pl);
-			id = prog->aux->id;
-			if (copy_to_user(prog_ids + i, &id, sizeof(id)))
-				return -EFAULT;
-			if (++i == cnt)
-				break;
+		if (prog_attach_flags) {
+			flags = cgrp->bpf.flags[atype];
+
+			for (i = 0; i < cnt; i++)
+				if (copy_to_user(prog_attach_flags + i, &flags, sizeof(flags)))
+					return -EFAULT;
+			prog_attach_flags += cnt;
 		}
+
+		prog_ids += cnt;
+		total_cnt -= cnt;
 	}
 	return ret;
 }

kernel/bpf/syscall.c

@@ -3520,7 +3520,7 @@ static int bpf_prog_detach(const union bpf_attr *attr)
 	}
 }
 
-#define BPF_PROG_QUERY_LAST_FIELD query.prog_cnt
+#define BPF_PROG_QUERY_LAST_FIELD query.prog_attach_flags
 
 static int bpf_prog_query(const union bpf_attr *attr,
 			  union bpf_attr __user *uattr)
@@ -3556,6 +3556,7 @@ static int bpf_prog_query(const union bpf_attr *attr,
 	case BPF_CGROUP_SYSCTL:
 	case BPF_CGROUP_GETSOCKOPT:
 	case BPF_CGROUP_SETSOCKOPT:
+	case BPF_LSM_CGROUP:
 		return cgroup_bpf_prog_query(attr, uattr);
 	case BPF_LIRC_MODE2:
 		return lirc_prog_query(attr, uattr);
@@ -4066,6 +4067,11 @@ static int bpf_prog_get_info_by_fd(struct file *file,
 
 	if (prog->aux->btf)
 		info.btf_id = btf_obj_id(prog->aux->btf);
+	info.attach_btf_id = prog->aux->attach_btf_id;
+	if (prog->aux->attach_btf)
+		info.attach_btf_obj_id = btf_obj_id(prog->aux->attach_btf);
+	else if (prog->aux->dst_prog)
+		info.attach_btf_obj_id = btf_obj_id(prog->aux->dst_prog->aux->attach_btf);
 
 	ulen = info.nr_func_info;
 	info.nr_func_info = prog->aux->func_info_cnt;