diff mbox series

[v5,12/37] lib: prevent module unloading if memory is not freed

Message ID 20240306182440.2003814-13-surenb@google.com (mailing list archive)
State New
Headers show
Series Memory allocation profiling | expand

Commit Message

Suren Baghdasaryan March 6, 2024, 6:24 p.m. UTC 
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    | 27 +++++++++++++++++++--------
 lib/codetag.c           | 11 ++++++++---
 3 files changed, 30 insertions(+), 14 deletions(-)

Comments

Luis Chamberlain March 12, 2024, 6:22 p.m. UTC | #1 
On Wed, Mar 06, 2024 at 10:24:10AM -0800, Suren Baghdasaryan wrote:
> 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.

So you just let them linger?

> Signed-off-by: Suren Baghdasaryan <surenb@google.com>


>  /* 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);
> +	if (!unload_codetags)
> +		pr_warn("%s: memory allocation(s) from the module still alive, cannot unload cleanly\n",
> +			mod->name);
> +

Because this is not unwinding anything. Should'd we check if we can
free all tags first, if we can't then we can't free the module. If we
can then ensure we don't enter a state where we can't later?

  Luis
Suren Baghdasaryan March 12, 2024, 6:41 p.m. UTC | #2 
On Tue, Mar 12, 2024 at 11:22 AM Luis Chamberlain <mcgrof@kernel.org> wrote:
>
> On Wed, Mar 06, 2024 at 10:24:10AM -0800, Suren Baghdasaryan wrote:
> > 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.
>
> So you just let them linger?

Well, I think this is not a normal situation when a module allocated
some memory and then is being unloaded without freeing that memory,
no?

>
> > Signed-off-by: Suren Baghdasaryan <surenb@google.com>
>
>
> >  /* 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);
> > +     if (!unload_codetags)
> > +             pr_warn("%s: memory allocation(s) from the module still alive, cannot unload cleanly\n",
> > +                     mod->name);
> > +
>
> Because this is not unwinding anything. Should'd we check if we can
> free all tags first, if we can't then we can't free the module. If we
> can then ensure we don't enter a state where we can't later?

unload_codetags already indicates that someone has a live reference to
one or more tags of that module, so we can't free them. Maybe I
misunderstood your suggestion?

>
>   Luis
diff mbox series

Patch

diff --git a/include/linux/codetag.h b/include/linux/codetag.h
index c44f5b83f24d..bfd0ba5c4185 100644
--- a/include/linux/codetag.h
+++ b/include/linux/codetag.h
@@ -35,7 +35,7 @@  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);
 };
 
@@ -71,10 +71,10 @@  codetag_register_type(const struct codetag_type_desc *desc);
 
 #if defined(CONFIG_CODE_TAGGING) && defined(CONFIG_MODULES)
 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 bf5a4afbe4c5..41c37ad3d16e 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 +1234,27 @@  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);
+	if (!unload_codetags)
+		pr_warn("%s: memory allocation(s) from the module still alive, cannot unload cleanly\n",
+			mod->name);
+
 	mod_sysfs_teardown(mod);
 
 	/*
@@ -1285,7 +1296,7 @@  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)
@@ -2298,7 +2309,7 @@  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;
 }
 
@@ -2428,7 +2439,7 @@  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 54d2828eba25..408062f722ce 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;
@@ -206,12 +207,13 @@  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) {
@@ -228,7 +230,8 @@  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);
@@ -237,6 +240,8 @@  void codetag_unload_module(struct module *mod)
 		up_write(&cttype->mod_lock);
 	}
 	mutex_unlock(&codetag_lock);
+
+	return unload_ok;
 }
 
 #else /* CONFIG_MODULES */