Merge branch 'Integrate kernel module BTF support'

Andrii Nakryiko says:

====================

This patch set adds BTF generation for kernel modules using a compact split
BTF approach. Respective patches have all the details.

Kernel module BTFs rely on pahole's split BTF support, which is added in [0]
and will be available starting from v1.19. Support for it is detected
automatically during kernel build time.

This patch set implements in-kernel support for split BTF loading and
validation. It also extends GET_OBJ_INFO API for BTFs to return BTF's module
name and a flag whether BTF itself is in-kernel or user-provided. vmlinux BTF
is also exposed to user-space through the same BTF object iteration APIs.

Follow up patch set will utilize the fact that vmlinux and module BTFs now
have associated ID to provide ability to attach BPF fentry/fexit/etc programs
to functions defined in kernel modules.

bpftool is also extended to show module/vmlinux BTF's name.

  [0] https://patchwork.kernel.org/project/netdevbpf/list/?series=378699&state=*

v3->v4:
  - copy_to_user() on ENOSPC in btf_get_info_by_fd() (Martin);
v2->v3:
  - get rid of unnecessary gotos (Song);
v2->v1:
  - drop WARNs, add fewer pr_warn()'s instead (Greg);
  - properly initialize sysfs binary attribute structure (Greg);
  - add __maybe_unused to any_section_objs, used conditionally by module BTF;
rfc->v1:
  - CONFIG_DEBUG_INFO_BTF_MODULES is derived automatically (Alexei);
  - vmlinux BTF now has explicit "vmlinux" name (Alexei);
  - added sysfs ABI documentation for /sys/kernel/btf/<module> (Greg).

Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
====================
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Documentation/ABI/testing/sysfs-kernel-btf

@@ -15,3 +15,11 @@ Description:
 		information with description of all internal kernel types. See
 		Documentation/bpf/btf.rst for detailed description of format
 		itself.
+
+What:		/sys/kernel/btf/<module-name>
+Date:		Nov 2020
+KernelVersion:	5.11
+Contact:	bpf@vger.kernel.org
+Description:
+		Read-only binary attribute exposing kernel module's BTF type
+		information as an add-on to the kernel's BTF (/sys/kernel/btf/vmlinux).

include/linux/bpf.h

@@ -36,9 +36,11 @@ struct seq_operations;
 struct bpf_iter_aux_info;
 struct bpf_local_storage;
 struct bpf_local_storage_map;
+struct kobject;
 
 extern struct idr btf_idr;
 extern spinlock_t btf_idr_lock;
+extern struct kobject *btf_kobj;
 
 typedef int (*bpf_iter_init_seq_priv_t)(void *private_data,
 					struct bpf_iter_aux_info *aux);

include/linux/module.h

@@ -475,6 +475,10 @@ struct module {
 	unsigned int num_bpf_raw_events;
 	struct bpf_raw_event_map *bpf_raw_events;
 #endif
+#ifdef CONFIG_DEBUG_INFO_BTF_MODULES
+	unsigned int btf_data_size;
+	void *btf_data;
+#endif
 #ifdef CONFIG_JUMP_LABEL
 	struct jump_entry *jump_entries;
 	unsigned int num_jump_entries;

include/uapi/linux/bpf.h

@@ -4466,6 +4466,9 @@ struct bpf_btf_info {
 	__aligned_u64 btf;
 	__u32 btf_size;
 	__u32 id;
+	__aligned_u64 name;
+	__u32 name_len;
+	__u32 kernel_btf;
 } __attribute__((aligned(8)));
 
 struct bpf_link_info {

kernel/bpf/sysfs_btf.c

@@ -26,7 +26,7 @@ static struct bin_attribute bin_attr_btf_vmlinux __ro_after_init = {
 	.read = btf_vmlinux_read,
 };
 
-static struct kobject *btf_kobj;
+struct kobject *btf_kobj;
 
 static int __init btf_vmlinux_init(void)
 {

kernel/module.c

@@ -380,6 +380,35 @@ static void *section_objs(const struct load_info *info,
 	return (void *)info->sechdrs[sec].sh_addr;
 }
 
+/* Find a module section: 0 means not found. Ignores SHF_ALLOC flag. */
+static unsigned int find_any_sec(const struct load_info *info, const char *name)
+{
+	unsigned int i;
+
+	for (i = 1; i < info->hdr->e_shnum; i++) {
+		Elf_Shdr *shdr = &info->sechdrs[i];
+		if (strcmp(info->secstrings + shdr->sh_name, name) == 0)
+			return i;
+	}
+	return 0;
+}
+
+/*
+ * Find a module section, or NULL. Fill in number of "objects" in section.
+ * Ignores SHF_ALLOC flag.
+ */
+static __maybe_unused void *any_section_objs(const struct load_info *info,
+					     const char *name,
+					     size_t object_size,
+					     unsigned int *num)
+{
+	unsigned int sec = find_any_sec(info, name);
+
+	/* Section 0 has sh_addr 0 and sh_size 0. */
+	*num = info->sechdrs[sec].sh_size / object_size;
+	return (void *)info->sechdrs[sec].sh_addr;
+}
+
 /* Provided by the linker */
 extern const struct kernel_symbol __start___ksymtab[];
 extern const struct kernel_symbol __stop___ksymtab[];
@@ -3250,6 +3279,9 @@ static int find_module_sections(struct module *mod, struct load_info *info)
 					   sizeof(*mod->bpf_raw_events),
 					   &mod->num_bpf_raw_events);
 #endif
+#ifdef CONFIG_DEBUG_INFO_BTF_MODULES
+	mod->btf_data = any_section_objs(info, ".BTF", 1, &mod->btf_data_size);
+#endif
 #ifdef CONFIG_JUMP_LABEL
 	mod->jump_entries = section_objs(info, "__jump_table",
 					sizeof(*mod->jump_entries),

lib/Kconfig.debug

@@ -274,6 +274,15 @@ config DEBUG_INFO_BTF
 	  Turning this on expects presence of pahole tool, which will convert
 	  DWARF type info into equivalent deduplicated BTF type info.
 
+config PAHOLE_HAS_SPLIT_BTF
+	def_bool $(success, test `$(PAHOLE) --version | sed -E 's/v([0-9]+)\.([0-9]+)/\1\2/'` -ge "119")
+
+config DEBUG_INFO_BTF_MODULES
+	def_bool y
+	depends on DEBUG_INFO_BTF && MODULES && PAHOLE_HAS_SPLIT_BTF
+	help
+	  Generate compact split BTF type information for kernel modules.
+
 config GDB_SCRIPTS
 	bool "Provide GDB scripts for kernel debugging"
 	help

scripts/Makefile.modfinal

@@ -6,6 +6,7 @@
 PHONY := __modfinal
 __modfinal:
 
+include include/config/auto.conf
 include $(srctree)/scripts/Kbuild.include
 
 # for c_flags
@@ -36,8 +37,23 @@ quiet_cmd_ld_ko_o = LD [M]  $@
 		-T scripts/module.lds -o $@ $(filter %.o, $^);		\
 	$(if $(ARCH_POSTLINK), $(MAKE) -f $(ARCH_POSTLINK) $@, true)
 
-$(modules): %.ko: %.o %.mod.o scripts/module.lds FORCE
-	+$(call if_changed,ld_ko_o)
+quiet_cmd_btf_ko = BTF [M] $@
+      cmd_btf_ko = LLVM_OBJCOPY=$(OBJCOPY) $(PAHOLE) -J --btf_base vmlinux $@
+
+# Same as newer-prereqs, but allows to exclude specified extra dependencies
+newer_prereqs_except = $(filter-out $(PHONY) $(1),$?)
+
+# Same as if_changed, but allows to exclude specified extra dependencies
+if_changed_except = $(if $(call newer_prereqs_except,$(2))$(cmd-check),      \
+	$(cmd);                                                              \
+	printf '%s\n' 'cmd_$@ := $(make-cmd)' > $(dot-target).cmd, @:)
+
+# Re-generate module BTFs if either module's .ko or vmlinux changed
+$(modules): %.ko: %.o %.mod.o scripts/module.lds vmlinux FORCE
+	+$(call if_changed_except,ld_ko_o,vmlinux)
+ifdef CONFIG_DEBUG_INFO_BTF_MODULES
+	+$(if $(newer-prereqs),$(call cmd,btf_ko))
+endif
 
 targets += $(modules) $(modules:.ko=.mod.o)
 

tools/bpf/bpftool/btf.c

@@ -742,9 +742,14 @@ show_btf_plain(struct bpf_btf_info *info, int fd,
 	       struct btf_attach_table *btf_map_table)
 {
 	struct btf_attach_point *obj;
+	const char *name = u64_to_ptr(info->name);
 	int n;
 
 	printf("%u: ", info->id);
+	if (info->kernel_btf)
+		printf("name [%s]  ", name);
+	else if (name && name[0])
+		printf("name %s  ", name);
 	printf("size %uB", info->btf_size);
 
 	n = 0;
@@ -771,6 +776,7 @@ show_btf_json(struct bpf_btf_info *info, int fd,
 	      struct btf_attach_table *btf_map_table)
 {
 	struct btf_attach_point *obj;
+	const char *name = u64_to_ptr(info->name);
 
 	jsonw_start_object(json_wtr);	/* btf object */
 	jsonw_uint_field(json_wtr, "id", info->id);
@@ -796,6 +802,11 @@ show_btf_json(struct bpf_btf_info *info, int fd,
 
 	emit_obj_refs_json(&refs_table, info->id, json_wtr); /* pids */
 
+	jsonw_bool_field(json_wtr, "kernel", info->kernel_btf);
+
+	if (name && name[0])
+		jsonw_string_field(json_wtr, "name", name);
+
 	jsonw_end_object(json_wtr);	/* btf object */
 }
 
@@ -803,15 +814,30 @@ static int
 show_btf(int fd, struct btf_attach_table *btf_prog_table,
 	 struct btf_attach_table *btf_map_table)
 {
-	struct bpf_btf_info info = {};
+	struct bpf_btf_info info;
 	__u32 len = sizeof(info);
+	char name[64];
 	int err;
 
+	memset(&info, 0, sizeof(info));
 	err = bpf_obj_get_info_by_fd(fd, &info, &len);
 	if (err) {
 		p_err("can't get BTF object info: %s", strerror(errno));
 		return -1;
 	}
+	/* if kernel support emitting BTF object name, pass name pointer */
+	if (info.name_len) {
+		memset(&info, 0, sizeof(info));
+		info.name_len = sizeof(name);
+		info.name = ptr_to_u64(name);
+		len = sizeof(info);
+
+		err = bpf_obj_get_info_by_fd(fd, &info, &len);
+		if (err) {
+			p_err("can't get BTF object info: %s", strerror(errno));
+			return -1;
+		}
+	}
 
 	if (json_output)
 		show_btf_json(&info, fd, btf_prog_table, btf_map_table);

tools/include/uapi/linux/bpf.h

@@ -4466,6 +4466,9 @@ struct bpf_btf_info {
 	__aligned_u64 btf;
 	__u32 btf_size;
 	__u32 id;
+	__aligned_u64 name;
+	__u32 name_len;
+	__u32 kernel_btf;
 } __attribute__((aligned(8)));
 
 struct bpf_link_info {