lkdtm: add usercopy tests

This adds test to detect copy_to_user/copy_from_user problems that are
protected by PAX_USERCOPY (and will be protected by HARDENED_USERCOPY).
Explicitly tests both "to" and "from" directions of heap object size
problems, heap object markings and, stack frame misalignment.

Signed-off-by: Kees Cook <keescook@chromium.org>

diff --git a/drivers/misc/lkdtm_core.c b/drivers/misc/lkdtm_core.c
index 187cd9b..3fe4b5d 100644 (file)
--- a/drivers/misc/lkdtm_core.c
+++ b/drivers/misc/lkdtm_core.c
@@ -111,7 +111,14 @@ enum ctype {
        CT_WRITE_RO,
        CT_WRITE_RO_AFTER_INIT,
        CT_WRITE_KERN,
-       CT_WRAP_ATOMIC
+       CT_WRAP_ATOMIC,
+       CT_USERCOPY_HEAP_SIZE_TO,
+       CT_USERCOPY_HEAP_SIZE_FROM,
+       CT_USERCOPY_HEAP_FLAG_TO,
+       CT_USERCOPY_HEAP_FLAG_FROM,
+       CT_USERCOPY_STACK_FRAME_TO,
+       CT_USERCOPY_STACK_FRAME_FROM,
+       CT_USERCOPY_STACK_BEYOND,
 };
 
 static char* cp_name[] = {
@@ -154,7 +161,14 @@ static char* cp_type[] = {
        "WRITE_RO",
        "WRITE_RO_AFTER_INIT",
        "WRITE_KERN",
-       "WRAP_ATOMIC"
+       "WRAP_ATOMIC",
+       "USERCOPY_HEAP_SIZE_TO",
+       "USERCOPY_HEAP_SIZE_FROM",
+       "USERCOPY_HEAP_FLAG_TO",
+       "USERCOPY_HEAP_FLAG_FROM",
+       "USERCOPY_STACK_FRAME_TO",
+       "USERCOPY_STACK_FRAME_FROM",
+       "USERCOPY_STACK_BEYOND",
 };
 
 static struct jprobe lkdtm;
@@ -166,6 +180,8 @@ static char* cpoint_name;
 static char* cpoint_type;
 static int cpoint_count = DEFAULT_COUNT;
 static int recur_count = REC_NUM_DEFAULT;
+static int alloc_size = 1024;
+static size_t cache_size;
 
 static enum cname cpoint = CN_INVALID;
 static enum ctype cptype = CT_NONE;
@@ -174,7 +190,9 @@ static DEFINE_SPINLOCK(count_lock);
 static DEFINE_SPINLOCK(lock_me_up);
 
 static u8 data_area[EXEC_SIZE];
+static struct kmem_cache *bad_cache;
 
+static const unsigned char test_text[] = "This is a test.\n";
 static const unsigned long rodata = 0xAA55AA55;
 static unsigned long ro_after_init __ro_after_init = 0x55AA5500;
 
@@ -188,6 +206,9 @@ MODULE_PARM_DESC(cpoint_type, " Crash Point Type, action to be taken on "\
 module_param(cpoint_count, int, 0644);
 MODULE_PARM_DESC(cpoint_count, " Crash Point Count, number of times the "\
                                "crash point is to be hit to trigger action");
+module_param(alloc_size, int, 0644);
+MODULE_PARM_DESC(alloc_size, " Size of allocation for user copy tests "\
+                            "(from 1 to PAGE_SIZE)");
 
 static unsigned int jp_do_irq(unsigned int irq)
 {
@@ -381,6 +402,228 @@ static void execute_user_location(void *dst)
        func();
 }
 
+/*
+ * Instead of adding -Wno-return-local-addr, just pass the stack address
+ * through a function to obfuscate it from the compiler.
+ */
+static noinline unsigned char *trick_compiler(unsigned char *stack)
+{
+       return stack + 0;
+}
+
+static noinline unsigned char *do_usercopy_stack_callee(int value)
+{
+       unsigned char buf[32];
+       int i;
+
+       /* Exercise stack to avoid everything living in registers. */
+       for (i = 0; i < sizeof(buf); i++) {
+               buf[i] = value & 0xff;
+       }
+
+       return trick_compiler(buf);
+}
+
+static noinline void do_usercopy_stack(bool to_user, bool bad_frame)
+{
+       unsigned long user_addr;
+       unsigned char good_stack[32];
+       unsigned char *bad_stack;
+       int i;
+
+       /* Exercise stack to avoid everything living in registers. */
+       for (i = 0; i < sizeof(good_stack); i++)
+               good_stack[i] = test_text[i % sizeof(test_text)];
+
+       /* This is a pointer to outside our current stack frame. */
+       if (bad_frame) {
+               bad_stack = do_usercopy_stack_callee(alloc_size);
+       } else {
+               /* Put start address just inside stack. */
+               bad_stack = task_stack_page(current) + THREAD_SIZE;
+               bad_stack -= sizeof(unsigned long);
+       }
+
+       user_addr = vm_mmap(NULL, 0, PAGE_SIZE,
+                           PROT_READ | PROT_WRITE | PROT_EXEC,
+                           MAP_ANONYMOUS | MAP_PRIVATE, 0);
+       if (user_addr >= TASK_SIZE) {
+               pr_warn("Failed to allocate user memory\n");
+               return;
+       }
+
+       if (to_user) {
+               pr_info("attempting good copy_to_user of local stack\n");
+               if (copy_to_user((void __user *)user_addr, good_stack,
+                                sizeof(good_stack))) {
+                       pr_warn("copy_to_user failed unexpectedly?!\n");
+                       goto free_user;
+               }
+
+               pr_info("attempting bad copy_to_user of distant stack\n");
+               if (copy_to_user((void __user *)user_addr, bad_stack,
+                                sizeof(good_stack))) {
+                       pr_warn("copy_to_user failed, but lacked Oops\n");
+                       goto free_user;
+               }
+       } else {
+               /*
+                * There isn't a safe way to not be protected by usercopy
+                * if we're going to write to another thread's stack.
+                */
+               if (!bad_frame)
+                       goto free_user;
+
+               pr_info("attempting good copy_from_user of local stack\n");
+               if (copy_from_user(good_stack, (void __user *)user_addr,
+                                  sizeof(good_stack))) {
+                       pr_warn("copy_from_user failed unexpectedly?!\n");
+                       goto free_user;
+               }
+
+               pr_info("attempting bad copy_from_user of distant stack\n");
+               if (copy_from_user(bad_stack, (void __user *)user_addr,
+                                  sizeof(good_stack))) {
+                       pr_warn("copy_from_user failed, but lacked Oops\n");
+                       goto free_user;
+               }
+       }
+
+free_user:
+       vm_munmap(user_addr, PAGE_SIZE);
+}
+
+static void do_usercopy_heap_size(bool to_user)
+{
+       unsigned long user_addr;
+       unsigned char *one, *two;
+       size_t size = clamp_t(int, alloc_size, 1, PAGE_SIZE);
+
+       one = kmalloc(size, GFP_KERNEL);
+       two = kmalloc(size, GFP_KERNEL);
+       if (!one || !two) {
+               pr_warn("Failed to allocate kernel memory\n");
+               goto free_kernel;
+       }
+
+       user_addr = vm_mmap(NULL, 0, PAGE_SIZE,
+                           PROT_READ | PROT_WRITE | PROT_EXEC,
+                           MAP_ANONYMOUS | MAP_PRIVATE, 0);
+       if (user_addr >= TASK_SIZE) {
+               pr_warn("Failed to allocate user memory\n");
+               goto free_kernel;
+       }
+
+       memset(one, 'A', size);
+       memset(two, 'B', size);
+
+       if (to_user) {
+               pr_info("attempting good copy_to_user of correct size\n");
+               if (copy_to_user((void __user *)user_addr, one, size)) {
+                       pr_warn("copy_to_user failed unexpectedly?!\n");
+                       goto free_user;
+               }
+
+               pr_info("attempting bad copy_to_user of too large size\n");
+               if (copy_to_user((void __user *)user_addr, one, 2 * size)) {
+                       pr_warn("copy_to_user failed, but lacked Oops\n");
+                       goto free_user;
+               }
+       } else {
+               pr_info("attempting good copy_from_user of correct size\n");
+               if (copy_from_user(one, (void __user *)user_addr,
+                                  size)) {
+                       pr_warn("copy_from_user failed unexpectedly?!\n");
+                       goto free_user;
+               }
+
+               pr_info("attempting bad copy_from_user of too large size\n");
+               if (copy_from_user(one, (void __user *)user_addr, 2 * size)) {
+                       pr_warn("copy_from_user failed, but lacked Oops\n");
+                       goto free_user;
+               }
+       }
+
+free_user:
+       vm_munmap(user_addr, PAGE_SIZE);
+free_kernel:
+       kfree(one);
+       kfree(two);
+}
+
+static void do_usercopy_heap_flag(bool to_user)
+{
+       unsigned long user_addr;
+       unsigned char *good_buf = NULL;
+       unsigned char *bad_buf = NULL;
+
+       /* Make sure cache was prepared. */
+       if (!bad_cache) {
+               pr_warn("Failed to allocate kernel cache\n");
+               return;
+       }
+
+       /*
+        * Allocate one buffer from each cache (kmalloc will have the
+        * SLAB_USERCOPY flag already, but "bad_cache" won't).
+        */
+       good_buf = kmalloc(cache_size, GFP_KERNEL);
+       bad_buf = kmem_cache_alloc(bad_cache, GFP_KERNEL);
+       if (!good_buf || !bad_buf) {
+               pr_warn("Failed to allocate buffers from caches\n");
+               goto free_alloc;
+       }
+
+       /* Allocate user memory we'll poke at. */
+       user_addr = vm_mmap(NULL, 0, PAGE_SIZE,
+                           PROT_READ | PROT_WRITE | PROT_EXEC,
+                           MAP_ANONYMOUS | MAP_PRIVATE, 0);
+       if (user_addr >= TASK_SIZE) {
+               pr_warn("Failed to allocate user memory\n");
+               goto free_alloc;
+       }
+
+       memset(good_buf, 'A', cache_size);
+       memset(bad_buf, 'B', cache_size);
+
+       if (to_user) {
+               pr_info("attempting good copy_to_user with SLAB_USERCOPY\n");
+               if (copy_to_user((void __user *)user_addr, good_buf,
+                                cache_size)) {
+                       pr_warn("copy_to_user failed unexpectedly?!\n");
+                       goto free_user;
+               }
+
+               pr_info("attempting bad copy_to_user w/o SLAB_USERCOPY\n");
+               if (copy_to_user((void __user *)user_addr, bad_buf,
+                                cache_size)) {
+                       pr_warn("copy_to_user failed, but lacked Oops\n");
+                       goto free_user;
+               }
+       } else {
+               pr_info("attempting good copy_from_user with SLAB_USERCOPY\n");
+               if (copy_from_user(good_buf, (void __user *)user_addr,
+                                  cache_size)) {
+                       pr_warn("copy_from_user failed unexpectedly?!\n");
+                       goto free_user;
+               }
+
+               pr_info("attempting bad copy_from_user w/o SLAB_USERCOPY\n");
+               if (copy_from_user(bad_buf, (void __user *)user_addr,
+                                  cache_size)) {
+                       pr_warn("copy_from_user failed, but lacked Oops\n");
+                       goto free_user;
+               }
+       }
+
+free_user:
+       vm_munmap(user_addr, PAGE_SIZE);
+free_alloc:
+       if (bad_buf)
+               kmem_cache_free(bad_cache, bad_buf);
+       kfree(good_buf);
+}
+
 static void lkdtm_do_action(enum ctype which)
 {
        switch (which) {
@@ -679,6 +922,27 @@ static void lkdtm_do_action(enum ctype which)
 
                return;
        }
+       case CT_USERCOPY_HEAP_SIZE_TO:
+               do_usercopy_heap_size(true);
+               break;
+       case CT_USERCOPY_HEAP_SIZE_FROM:
+               do_usercopy_heap_size(false);
+               break;
+       case CT_USERCOPY_HEAP_FLAG_TO:
+               do_usercopy_heap_flag(true);
+               break;
+       case CT_USERCOPY_HEAP_FLAG_FROM:
+               do_usercopy_heap_flag(false);
+               break;
+       case CT_USERCOPY_STACK_FRAME_TO:
+               do_usercopy_stack(true, true);
+               break;
+       case CT_USERCOPY_STACK_FRAME_FROM:
+               do_usercopy_stack(false, true);
+               break;
+       case CT_USERCOPY_STACK_BEYOND:
+               do_usercopy_stack(true, false);
+               break;
        case CT_NONE:
        default:
                break;
@@ -971,6 +1235,11 @@ static int __init lkdtm_module_init(void)
        /* Make sure we can write to __ro_after_init values during __init */
        ro_after_init |= 0xAA;
 
+       /* Prepare cache that lacks SLAB_USERCOPY flag. */
+       cache_size = clamp_t(int, alloc_size, 1, PAGE_SIZE);
+       bad_cache = kmem_cache_create("lkdtm-no-usercopy", cache_size, 0,
+                                     0, NULL);
+
        /* Register debugfs interface */
        lkdtm_debugfs_root = debugfs_create_dir("provoke-crash", NULL);
        if (!lkdtm_debugfs_root) {
@@ -1022,6 +1291,8 @@ static void __exit lkdtm_module_exit(void)
 {
        debugfs_remove_recursive(lkdtm_debugfs_root);
 
+       kmem_cache_destroy(bad_cache);
+
        unregister_jprobe(&lkdtm);
        pr_info("Crash point unregistered\n");
 }