bpf: Refactor reporting log_true_size for prog_load

The next commit will add support for reporting logs via extended common
attributes, including 'log_true_size'.

To prepare for that, refactor the 'log_true_size' reporting logic by
introducing a new struct bpf_log_attr to encapsulate log-related behavior:

 * bpf_log_attr_init(): initialize log fields, which will support
   extended common attributes in the next commit.
 * bpf_log_attr_finalize(): handle log finalization and write back
   'log_true_size' to userspace.

Acked-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
Link: https://lore.kernel.org/r/20260512153157.28382-4-leon.hwang@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

include/linux/bpf.h

@@ -2919,7 +2919,9 @@ int bpf_check_uarg_tail_zero(bpfptr_t uaddr, size_t expected_size,
 			     size_t actual_size);
 
 /* verify correctness of eBPF program */
-int bpf_check(struct bpf_prog **fp, union bpf_attr *attr, bpfptr_t uattr, u32 uattr_size);
+struct bpf_log_attr;
+int bpf_check(struct bpf_prog **fp, union bpf_attr *attr, bpfptr_t uattr,
+	      struct bpf_log_attr *attr_log);
 
 #ifndef CONFIG_BPF_JIT_ALWAYS_ON
 void bpf_patch_call_args(struct bpf_insn *insn, u32 stack_depth);

include/linux/bpf_verifier.h

@@ -755,6 +755,18 @@ static inline bool bpf_verifier_log_needed(const struct bpf_verifier_log *log)
 	return log && log->level;
 }
 
+struct bpf_log_attr {
+	char __user *ubuf;
+	u32 size;
+	u32 level;
+	u32 offsetof_true_size;
+	bpfptr_t uattr;
+};
+
+int bpf_log_attr_init(struct bpf_log_attr *log, u64 log_buf, u32 log_size, u32 log_level,
+		      u32 offsetof_log_true_size, bpfptr_t uattr);
+int bpf_log_attr_finalize(struct bpf_log_attr *attr, struct bpf_verifier_log *log);
+
 #define BPF_MAX_SUBPROGS 256
 
 struct bpf_subprog_arg_info {

kernel/bpf/log.c

@@ -825,3 +825,32 @@ void print_insn_state(struct bpf_verifier_env *env, const struct bpf_verifier_st
 	}
 	print_verifier_state(env, vstate, frameno, false);
 }
+
+int bpf_log_attr_init(struct bpf_log_attr *log, u64 log_buf, u32 log_size, u32 log_level,
+		      u32 offsetof_log_true_size, bpfptr_t uattr)
+{
+	char __user *ubuf = u64_to_user_ptr(log_buf);
+
+	memset(log, 0, sizeof(*log));
+	log->ubuf = ubuf;
+	log->size = log_size;
+	log->level = log_level;
+	log->offsetof_true_size = offsetof_log_true_size;
+	log->uattr = uattr;
+	return 0;
+}
+
+int bpf_log_attr_finalize(struct bpf_log_attr *attr, struct bpf_verifier_log *log)
+{
+	u32 log_true_size;
+	int err;
+
+	err = bpf_vlog_finalize(log, &log_true_size);
+
+	if (attr->offsetof_true_size &&
+	    copy_to_bpfptr_offset(attr->uattr, attr->offsetof_true_size, &log_true_size,
+				  sizeof(log_true_size)))
+		return -EFAULT;
+
+	return err;
+}

kernel/bpf/syscall.c

@@ -2861,7 +2861,7 @@ static int bpf_prog_mark_insn_arrays_ready(struct bpf_prog *prog)
 /* last field in 'union bpf_attr' used by this command */
 #define BPF_PROG_LOAD_LAST_FIELD keyring_id
 
-static int bpf_prog_load(union bpf_attr *attr, bpfptr_t uattr, u32 uattr_size)
+static int bpf_prog_load(union bpf_attr *attr, bpfptr_t uattr, struct bpf_log_attr *attr_log)
 {
 	enum bpf_prog_type type = attr->prog_type;
 	struct bpf_prog *prog, *dst_prog = NULL;
@@ -3079,7 +3079,7 @@ static int bpf_prog_load(union bpf_attr *attr, bpfptr_t uattr, u32 uattr_size)
 		goto free_prog_sec;
 
 	/* run eBPF verifier */
-	err = bpf_check(&prog, attr, uattr, uattr_size);
+	err = bpf_check(&prog, attr, uattr, attr_log);
 	if (err < 0)
 		goto free_used_maps;
 
@@ -6215,6 +6215,8 @@ static int __sys_bpf(enum bpf_cmd cmd, bpfptr_t uattr, unsigned int size,
 		     bpfptr_t uattr_common, unsigned int size_common)
 {
 	struct bpf_common_attr attr_common;
+	u32 offsetof_log_true_size = 0;
+	struct bpf_log_attr attr_log;
 	union bpf_attr attr;
 	int err;
 
@@ -6266,7 +6268,11 @@ static int __sys_bpf(enum bpf_cmd cmd, bpfptr_t uattr, unsigned int size,
 		err = map_freeze(&attr);
 		break;
 	case BPF_PROG_LOAD:
-		err = bpf_prog_load(&attr, uattr, size);
+		if (size >= offsetofend(union bpf_attr, log_true_size))
+			offsetof_log_true_size = offsetof(union bpf_attr, log_true_size);
+		err = bpf_log_attr_init(&attr_log, attr.log_buf, attr.log_size, attr.log_level,
+					offsetof_log_true_size, uattr);
+		err = err ?: bpf_prog_load(&attr, uattr, &attr_log);
 		break;
 	case BPF_OBJ_PIN:
 		err = bpf_obj_pin(&attr);

kernel/bpf/verifier.c

@@ -19294,12 +19294,12 @@ int bpf_fixup_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
 	return 0;
 }
 
-int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr, __u32 uattr_size)
+int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr,
+	      struct bpf_log_attr *attr_log)
 {
 	u64 start_time = ktime_get_ns();
 	struct bpf_verifier_env *env;
 	int i, len, ret = -EINVAL, err;
-	u32 log_true_size;
 	bool is_priv;
 
 	BTF_TYPE_EMIT(enum bpf_features);
@@ -19346,9 +19346,7 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr, __u3
 	/* user could have requested verbose verifier output
 	 * and supplied buffer to store the verification trace
 	 */
-	ret = bpf_vlog_init(&env->log, attr->log_level,
-			    (char __user *) (unsigned long) attr->log_buf,
-			    attr->log_size);
+	ret = bpf_vlog_init(&env->log, attr_log->level, attr_log->ubuf, attr_log->size);
 	if (ret)
 		goto err_unlock;
 
@@ -19510,17 +19508,10 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr, __u3
 	env->prog->aux->verified_insns = env->insn_processed;
 
 	/* preserve original error even if log finalization is successful */
-	err = bpf_vlog_finalize(&env->log, &log_true_size);
+	err = bpf_log_attr_finalize(attr_log, &env->log);
 	if (err)
 		ret = err;
 
-	if (uattr_size >= offsetofend(union bpf_attr, log_true_size) &&
-	    copy_to_bpfptr_offset(uattr, offsetof(union bpf_attr, log_true_size),
-				  &log_true_size, sizeof(log_true_size))) {
-		ret = -EFAULT;
-		goto err_release_maps;
-	}
-
 	if (ret)
 		goto err_release_maps;