[RFC bpf-next 1/3] bpf: add module support to btf display helpers

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bpf_snprintf_btf and bpf_seq_printf_btf use a "struct btf_ptr *"
argument that specifies type information about the type to
be displayed.  Augment this information to include a module
name, allowing such display to support module types.

Signed-off-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
---
 include/linux/btf.h            |  8 ++++++++
 include/uapi/linux/bpf.h       |  5 ++++-
 kernel/bpf/btf.c               | 18 ++++++++++++++++++
 kernel/trace/bpf_trace.c       | 42 ++++++++++++++++++++++++++++++++----------
 tools/include/uapi/linux/bpf.h |  5 ++++-
 5 files changed, 66 insertions(+), 12 deletions(-)

diff --git a/include/linux/btf.h b/include/linux/btf.h
index 2bf6418..d55ca00 100644
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -209,6 +209,14 @@ static inline const struct btf_var_secinfo *btf_type_var_secinfo(
 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);
+#ifdef CONFIG_DEBUG_INFO_BTF_MODULES
+struct btf *bpf_get_btf_module(const char *name);
+#else
+static inline struct btf *bpf_get_btf_module(const char *name)
+{
+	return ERR_PTR(-ENOTSUPP);
+}
+#endif
 struct btf *bpf_prog_get_target_btf(const struct bpf_prog *prog);
 #else
 static inline const struct btf_type *btf_type_by_id(const struct btf *btf,
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 162999b..26978be 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -3636,7 +3636,8 @@ struct bpf_stack_build_id {
  *		the pointer data is carried out to avoid kernel crashes during
  *		operation.  Smaller types can use string space on the stack;
  *		larger programs can use map data to store the string
- *		representation.
+ *		representation.  Module-specific data structures can be
+ *		displayed if the module name is supplied.
  *
  *		The string can be subsequently shared with userspace via
  *		bpf_perf_event_output() or ring buffer interfaces.
@@ -5076,11 +5077,13 @@ struct bpf_sk_lookup {
  * potentially to specify additional details about the BTF pointer
  * (rather than its mode of display) - is included for future use.
  * Display flags - BTF_F_* - are passed to bpf_snprintf_btf separately.
+ * A module name can be specified for module-specific data.
  */
 struct btf_ptr {
 	void *ptr;
 	__u32 type_id;
 	__u32 flags;		/* BTF ptr flags; unused at present. */
+	const char *module;	/* optional module name. */
 };
 
 /*
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 6b2d508..3ddd1fd 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -5738,6 +5738,24 @@ struct btf_module {
 static LIST_HEAD(btf_modules);
 static DEFINE_MUTEX(btf_module_mutex);
 
+struct btf *bpf_get_btf_module(const char *name)
+{
+	struct btf *btf = ERR_PTR(-ENOENT);
+	struct btf_module *btf_mod, *tmp;
+
+	mutex_lock(&btf_module_mutex);
+	list_for_each_entry_safe(btf_mod, tmp, &btf_modules, list) {
+		if (!btf_mod->btf || strcmp(name, btf_mod->btf->name) != 0)
+			continue;
+
+		refcount_inc(&btf_mod->btf->refcnt);
+		btf = btf_mod->btf;
+		break;
+	}
+	mutex_unlock(&btf_module_mutex);
+	return btf;
+}
+
 static ssize_t
 btf_module_read(struct file *file, struct kobject *kobj,
 		struct bin_attribute *bin_attr,
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index cfce60a..a4d5a26 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -73,8 +73,7 @@ static struct bpf_raw_event_map *bpf_get_raw_tracepoint_module(const char *name)
 u64 bpf_get_stack(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5);
 
 static int bpf_btf_printf_prepare(struct btf_ptr *ptr, u32 btf_ptr_size,
-				  u64 flags, const struct btf **btf,
-				  s32 *btf_id);
+				  u64 flags, struct btf **btf, s32 *btf_id);
 
 /**
  * trace_call_bpf - invoke BPF program
@@ -784,7 +783,7 @@ struct bpf_seq_printf_buf {
 BPF_CALL_4(bpf_seq_printf_btf, struct seq_file *, m, struct btf_ptr *, ptr,
 	   u32, btf_ptr_size, u64, flags)
 {
-	const struct btf *btf;
+	struct btf *btf;
 	s32 btf_id;
 	int ret;
 
@@ -792,7 +791,11 @@ struct bpf_seq_printf_buf {
 	if (ret)
 		return ret;
 
-	return btf_type_seq_show_flags(btf, btf_id, ptr->ptr, m, flags);
+	ret = btf_type_seq_show_flags(btf, btf_id, ptr->ptr, m, flags);
+	if (btf_ptr_size == sizeof(struct btf_ptr) && ptr->module)
+		btf_put(btf);
+
+	return ret;
 }
 
 static const struct bpf_func_proto bpf_seq_printf_btf_proto = {
@@ -1199,18 +1202,33 @@ static bool bpf_d_path_allowed(const struct bpf_prog *prog)
 			 BTF_F_PTR_RAW | BTF_F_ZERO)
 
 static int bpf_btf_printf_prepare(struct btf_ptr *ptr, u32 btf_ptr_size,
-				  u64 flags, const struct btf **btf,
+				  u64 flags, struct btf **btf,
 				  s32 *btf_id)
 {
+	char modname[MODULE_NAME_LEN];
 	const struct btf_type *t;
+	int ret;
 
 	if (unlikely(flags & ~(BTF_F_ALL)))
 		return -EINVAL;
 
-	if (btf_ptr_size != sizeof(struct btf_ptr))
+	/* For backwards compatibility, ensure that we support BPF
+	 * programs compiled with older "struct btf_ptr" definitions
+	 * that lacked the "module" field.
+	 */
+	if (btf_ptr_size != sizeof(struct btf_ptr) &&
+	    btf_ptr_size != sizeof(struct btf_ptr) - sizeof(char *))
 		return -EINVAL;
 
-	*btf = bpf_get_btf_vmlinux();
+	if (btf_ptr_size == sizeof(struct btf_ptr) && ptr->module) {
+		ret = copy_from_kernel_nofault(modname, ptr->module,
+					       sizeof(modname));
+		if (ret)
+			return ret;
+
+		*btf = bpf_get_btf_module(modname);
+	} else
+		*btf = bpf_get_btf_vmlinux();
 
 	if (IS_ERR_OR_NULL(*btf))
 		return PTR_ERR(*btf);
@@ -1231,7 +1249,7 @@ static int bpf_btf_printf_prepare(struct btf_ptr *ptr, u32 btf_ptr_size,
 BPF_CALL_5(bpf_snprintf_btf, char *, str, u32, str_size, struct btf_ptr *, ptr,
 	   u32, btf_ptr_size, u64, flags)
 {
-	const struct btf *btf;
+	struct btf *btf;
 	s32 btf_id;
 	int ret;
 
@@ -1239,8 +1257,12 @@ static int bpf_btf_printf_prepare(struct btf_ptr *ptr, u32 btf_ptr_size,
 	if (ret)
 		return ret;
 
-	return btf_type_snprintf_show(btf, btf_id, ptr->ptr, str, str_size,
-				      flags);
+	ret = btf_type_snprintf_show(btf, btf_id, ptr->ptr, str, str_size,
+				     flags);
+	if (btf_ptr_size == sizeof(struct btf_ptr) && ptr->module)
+		btf_put(btf);
+
+	return ret;
 }
 
 const struct bpf_func_proto bpf_snprintf_btf_proto = {
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 162999b..26978be 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -3636,7 +3636,8 @@ struct bpf_stack_build_id {
  *		the pointer data is carried out to avoid kernel crashes during
  *		operation.  Smaller types can use string space on the stack;
  *		larger programs can use map data to store the string
- *		representation.
+ *		representation.  Module-specific data structures can be
+ *		displayed if the module name is supplied.
  *
  *		The string can be subsequently shared with userspace via
  *		bpf_perf_event_output() or ring buffer interfaces.
@@ -5076,11 +5077,13 @@ struct bpf_sk_lookup {
  * potentially to specify additional details about the BTF pointer
  * (rather than its mode of display) - is included for future use.
  * Display flags - BTF_F_* - are passed to bpf_snprintf_btf separately.
+ * A module name can be specified for module-specific data.
  */
 struct btf_ptr {
 	void *ptr;
 	__u32 type_id;
 	__u32 flags;		/* BTF ptr flags; unused at present. */
+	const char *module;	/* optional module name. */
 };
 
 /*
-- 
1.8.3.1




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