[PATCH 07/14] module: Add module_kallsyms_on_each_core_symbol()

module_kallsyms_on_each_symbol() iterates mod->kallsyms, which points at
the full init symbol table until do_init_module() swaps it out.  The set
of symbols it reports thus differs based on whether init memory has been
freed yet.

Add module_kallsyms_on_each_core_symbol() for callers which need a
symbol's position to be the same before and after that swap.
core_kallsyms is fully populated by add_kallsyms() before the module
leaves MODULE_STATE_UNFORMED, so it's readable on both paths.

Signed-off-by: Josh Poimboeuf <[email protected]>
---
 include/linux/module.h   | 11 ++++++++++
 kernel/module/kallsyms.c | 46 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 57 insertions(+)

diff --git a/include/linux/module.h b/include/linux/module.h
index 7566815fabbe..4ea4522a5fc5 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -947,6 +947,9 @@ static inline bool module_sig_ok(struct module *module)
 int module_kallsyms_on_each_symbol(const char *modname,
 				   int (*fn)(void *, const char *, unsigned long),
 				   void *data);
+int module_kallsyms_on_each_core_symbol(const char *modname,
+					int (*fn)(void *, const char *, unsigned long),
+					void *data);
 
 /* For kallsyms to ask for address resolution.  namebuf should be at
  * least KSYM_NAME_LEN long: a pointer to namebuf is returned if
@@ -984,6 +987,14 @@ static inline int module_kallsyms_on_each_symbol(const char *modname,
 	return -EOPNOTSUPP;
 }
 
+static inline int
+module_kallsyms_on_each_core_symbol(const char *modname,
+				    int (*fn)(void *, const char *, unsigned long),
+				    void *data)
+{
+	return -EOPNOTSUPP;
+}
+
 /* For kallsyms to ask for address resolution.  NULL means not found. */
 static inline int module_address_lookup(unsigned long addr,
 						unsigned long *symbolsize,
diff --git a/kernel/module/kallsyms.c b/kernel/module/kallsyms.c
index 0fc11e45df9b..3a959c3c9f9b 100644
--- a/kernel/module/kallsyms.c
+++ b/kernel/module/kallsyms.c
@@ -494,3 +494,49 @@ int module_kallsyms_on_each_symbol(const char *modname,
 	mutex_unlock(&module_mutex);
 	return ret;
 }
+
+/*
+ * Iterate @modname's cut-down core symbol table, rather than mod->kallsyms
+ * which points at the full init symbol table until do_init_module() swaps it
+ * out.  For callers which need a symbol's position to be the same before and
+ * after that swap.
+ *
+ * core_kallsyms is populated by add_kallsyms(), which runs before the module
+ * leaves MODULE_STATE_UNFORMED.
+ *
+ * Unlike module_kallsyms_on_each_symbol(), @modname is required.
+ */
+int module_kallsyms_on_each_core_symbol(const char *modname,
+					int (*fn)(void *, const char *, unsigned long),
+					void *data)
+{
+	struct mod_kallsyms *kallsyms;
+	struct module *mod;
+	unsigned int i;
+	int ret = 0;
+
+	if (!modname)
+		return -EINVAL;
+
+	guard(mutex)(&module_mutex);
+
+	mod = find_module_all(modname, strlen(modname), false);
+	if (!mod)
+		return -ENOENT;
+
+	kallsyms = &mod->core_kallsyms;
+
+	for (i = 0; i < kallsyms->num_symtab; i++) {
+		const Elf_Sym *sym = &kallsyms->symtab[i];
+
+		if (sym->st_shndx == SHN_UNDEF)
+			continue;
+
+		ret = fn(data, kallsyms_symbol_name(kallsyms, i),
+			 kallsyms_symbol_value(sym));
+		if (ret)
+			break;
+	}
+
+	return ret;
+}
-- 
2.54.0