[PATCH v6 12/37] lib: prevent module unloading if memory is not freed

Suren Baghdasaryan
2024-03-21T16:37:36Z

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(-)

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 ffa6b3e9cb43..2d25eebc549d 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 */
--
2.44.0.291.gc1ea87d7ee-goog