kbuild, btf: Expose vmlinux inline BTF through sysfs

Expose BTF inline-location information from vmlinux .BTF.inline
sections in /sys/kernel/btf as vmlinux.inline. Embedded vmlinux
inline BTF supports read-only mmap().

Provide runtime support for a module-delivered vmlinux inline BTF
carrier. Its link record binds the carrier module name, BTF size, and
SHA-256 digest to the running kernel before its data is made available
through a lazy vmlinux.inline sysfs attribute. The carrier is handled
before ordinary module BTF registration, so its incidental .BTF data is
not exposed.

Make CONFIG_DEBUG_INFO_BTF_INLINE tristate. When configured as a
module, retain vmlinux final split inline BTF for
btf_vmlinux_inline.ko instead of embedding it in vmlinux.

Reserve .BTF.inline.link in vmlinux and extend the final
resolve_btfids patch pass to bind btf_vmlinux_inline to the raw
vmlinux.BTF.inline payload. This preserves the normal built-in
configuration while allowing the large inline BTF payload to load on
demand.

Normal module inline BTF is handled separately, after its
references have been relocated against the final module BTF.

Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://patch.msgid.link/20261009112324.1442319-4-alan.maguire@oracle.com

2 files changed, 41 insertions, 0 deletions

diff --git a/include/linux/btf.h b/include/linux/btf.h
index 4b63bb91550a..f731c7a5f14c 100644
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -5,6 +5,7 @@
 #define _LINUX_BTF_H 1
 
 #include <linux/types.h>
+#include <linux/module.h>
 #include <linux/bpfptr.h>
 #include <linux/bsearch.h>
 #include <linux/btf_ids.h>
@@ -118,6 +119,19 @@ struct btf_show;
 struct btf_id_set;
 struct bpf_prog;
 
+#define BTF_LINK_SHA256_LEN	32
+
+/*
+ * A .BTF.link or .BTF.inline.link section identifies the module which
+ * carries a vmlinux BTF section.  The module name is NUL terminated and the
+ * field is padded to __MODULE_NAME_LEN.
+ */
+struct btf_link {
+	char module_name[__MODULE_NAME_LEN];
+	u8 sha256[BTF_LINK_SHA256_LEN];
+	u32 btf_size;
+} __packed;
+
 typedef int (*btf_kfunc_filter_t)(const struct bpf_prog *prog, u32 kfunc_id);
 
 struct btf_kfunc_id_set {
@@ -624,6 +638,29 @@ bool btf_types_are_same(const struct btf *btf1, u32 id1,
 			const struct btf *btf2, u32 id2);
 int btf_check_iter_arg(struct btf *btf, const struct btf_type *func, int arg_idx);
 
+#if IS_ENABLED(CONFIG_SYSFS)
+struct bin_attribute *sysfs_btf_add(const char *name, void *data, size_t data_size,
+				    bool mmap, const char *lazy_module_name);
+bool sysfs_btf_update(struct bin_attribute *attr, void *data);
+void sysfs_btf_remove(struct bin_attribute *attr);
+#else
+static inline struct bin_attribute *
+sysfs_btf_add(const char *name, void *data, size_t data_size, bool mmap,
+	      const char *lazy_module_name)
+{
+	return NULL;
+}
+
+static inline bool sysfs_btf_update(struct bin_attribute *attr, void *data)
+{
+	return false;
+}
+
+static inline void sysfs_btf_remove(struct bin_attribute *attr)
+{
+}
+#endif
+
 static inline bool btf_type_is_struct_ptr(struct btf *btf, const struct btf_type *t)
 {
 	if (!btf_type_is_ptr(t))
diff --git a/include/linux/module.h b/include/linux/module.h
index 96cc98568eea..a6abde12a458 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -503,6 +503,10 @@ struct module {
 	void *btf_data;
 	void *btf_base_data;
 #endif
+#if IS_ENABLED(CONFIG_DEBUG_INFO_BTF_INLINE)
+	unsigned int btf_inline_data_size;
+	void *btf_inline_data;
+#endif
 #ifdef CONFIG_JUMP_LABEL
 	struct jump_entry *jump_entries;
 	unsigned int num_jump_entries;