From aa981a665d587a19be869ce7f3cb7232f8588dd8 Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Fri, 3 Jun 2016 12:06:52 -0700 Subject: [PATCH] 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 --- drivers/misc/lkdtm_core.c | 275 +++++++++++++++++++++++++++++++++++++- 1 file changed, 273 insertions(+), 2 deletions(-) diff --git a/drivers/misc/lkdtm_core.c b/drivers/misc/lkdtm_core.c index 187cd9b63e9a..3fe4b5dee955 100644 --- 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"); }