[PATCH v2 14/39] lib: prevent module unloading if memory is not freed

[Suren Baghdasaryan <surenb@google.com>]

Skip freeing module's data section if there are non-zero allocation tags
because otherwise, once these allocations are freed, the access to their
code tag would cause UAF.

Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
 include/linux/codetag.h |  6 +++---
 kernel/module/main.c    | 23 +++++++++++++++--------
 lib/codetag.c           | 11 ++++++++---
 3 files changed, 26 insertions(+), 14 deletions(-)

diff --git a/include/linux/codetag.h b/include/linux/codetag.h
index 386733e89b31..d98e4c8e86f0 100644
--- a/include/linux/codetag.h
+++ b/include/linux/codetag.h
@@ -44,7 +44,7 @@ struct codetag_type_desc {
 	size_t tag_size;
 	void (*module_load)(struct codetag_type *cttype,
 			    struct codetag_module *cmod);
-	void (*module_unload)(struct codetag_type *cttype,
+	bool (*module_unload)(struct codetag_type *cttype,
 			      struct codetag_module *cmod);
 };
 
@@ -74,10 +74,10 @@ codetag_register_type(const struct codetag_type_desc *desc);
 
 #ifdef CONFIG_CODE_TAGGING
 void codetag_load_module(struct module *mod);
-void codetag_unload_module(struct module *mod);
+bool codetag_unload_module(struct module *mod);
 #else
 static inline void codetag_load_module(struct module *mod) {}
-static inline void codetag_unload_module(struct module *mod) {}
+static inline bool codetag_unload_module(struct module *mod) { return true; }
 #endif
 
 #endif /* _LINUX_CODETAG_H */
diff --git a/kernel/module/main.c b/kernel/module/main.c
index c0d3f562c7ab..079f40792ce8 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -1211,15 +1211,19 @@ static void *module_memory_alloc(unsigned int size, enum mod_mem_type type)
 	return module_alloc(size);
 }
 
-static void module_memory_free(void *ptr, enum mod_mem_type type)
+static void module_memory_free(void *ptr, enum mod_mem_type type,
+			       bool unload_codetags)
 {
+	if (!unload_codetags && mod_mem_type_is_core_data(type))
+		return;
+
 	if (mod_mem_use_vmalloc(type))
 		vfree(ptr);
 	else
 		module_memfree(ptr);
 }
 
-static void free_mod_mem(struct module *mod)
+static void free_mod_mem(struct module *mod, bool unload_codetags)
 {
 	for_each_mod_mem_type(type) {
 		struct module_memory *mod_mem = &mod->mem[type];
@@ -1230,20 +1234,23 @@ static void free_mod_mem(struct module *mod)
 		/* Free lock-classes; relies on the preceding sync_rcu(). */
 		lockdep_free_key_range(mod_mem->base, mod_mem->size);
 		if (mod_mem->size)
-			module_memory_free(mod_mem->base, type);
+			module_memory_free(mod_mem->base, type,
+					   unload_codetags);
 	}
 
 	/* MOD_DATA hosts mod, so free it at last */
 	lockdep_free_key_range(mod->mem[MOD_DATA].base, mod->mem[MOD_DATA].size);
-	module_memory_free(mod->mem[MOD_DATA].base, MOD_DATA);
+	module_memory_free(mod->mem[MOD_DATA].base, MOD_DATA, unload_codetags);
 }
 
 /* Free a module, remove from lists, etc. */
 static void free_module(struct module *mod)
 {
+	bool unload_codetags;
+
 	trace_module_free(mod);
 
-	codetag_unload_module(mod);
+	unload_codetags = codetag_unload_module(mod);
 	mod_sysfs_teardown(mod);
 
 	/*
@@ -1285,7 +1292,7 @@ static void free_module(struct module *mod)
 	kfree(mod->args);
 	percpu_modfree(mod);
 
-	free_mod_mem(mod);
+	free_mod_mem(mod, unload_codetags);
 }
 
 void *__symbol_get(const char *symbol)
@@ -2295,7 +2302,7 @@ static int move_module(struct module *mod, struct load_info *info)
 	return 0;
 out_enomem:
 	for (t--; t >= 0; t--)
-		module_memory_free(mod->mem[t].base, t);
+		module_memory_free(mod->mem[t].base, t, true);
 	return ret;
 }
 
@@ -2425,7 +2432,7 @@ static void module_deallocate(struct module *mod, struct load_info *info)
 	percpu_modfree(mod);
 	module_arch_freeing_init(mod);
 
-	free_mod_mem(mod);
+	free_mod_mem(mod, true);
 }
 
 int __weak module_finalize(const Elf_Ehdr *hdr,
diff --git a/lib/codetag.c b/lib/codetag.c
index 4ea57fb37346..0ad4ea66c769 100644
--- a/lib/codetag.c
+++ b/lib/codetag.c
@@ -5,6 +5,7 @@
 #include <linux/module.h>
 #include <linux/seq_buf.h>
 #include <linux/slab.h>
+#include <linux/vmalloc.h>
 
 struct codetag_type {
 	struct list_head link;
@@ -219,12 +220,13 @@ void codetag_load_module(struct module *mod)
 	mutex_unlock(&codetag_lock);
 }
 
-void codetag_unload_module(struct module *mod)
+bool codetag_unload_module(struct module *mod)
 {
 	struct codetag_type *cttype;
+	bool unload_ok = true;
 
 	if (!mod)
-		return;
+		return true;
 
 	mutex_lock(&codetag_lock);
 	list_for_each_entry(cttype, &codetag_types, link) {
@@ -241,7 +243,8 @@ void codetag_unload_module(struct module *mod)
 		}
 		if (found) {
 			if (cttype->desc.module_unload)
-				cttype->desc.module_unload(cttype, cmod);
+				if (!cttype->desc.module_unload(cttype, cmod))
+					unload_ok = false;
 
 			cttype->count -= range_size(cttype, &cmod->range);
 			idr_remove(&cttype->mod_idr, mod_id);
@@ -250,4 +253,6 @@ void codetag_unload_module(struct module *mod)
 		up_write(&cttype->mod_lock);
 	}
 	mutex_unlock(&codetag_lock);
+
+	return unload_ok;
 }
-- 
2.42.0.758.gaed0368e0e-goog