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Message-Id: <1465336628-18219-5-git-send-email-keescook@chromium.org>
Date: Tue, 7 Jun 2016 14:57:07 -0700
From: Kees Cook <keescook@...omium.org>
To: kernel-hardening@...ts.openwall.com
Cc: Kees Cook <keescook@...omium.org>,
Arnd Bergmann <arnd@...db.de>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Andrew Morton <akpm@...ux-foundation.org>,
"David S. Miller" <davem@...emloft.net>,
Mauro Carvalho Chehab <mchehab@....samsung.com>,
Jiri Slaby <jslaby@...e.cz>,
Guenter Roeck <linux@...ck-us.net>,
linux-kernel@...r.kernel.org
Subject: [PATCH 4/5] 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@...omium.org>
---
drivers/misc/lkdtm_core.c | 255 +++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 253 insertions(+), 2 deletions(-)
diff --git a/drivers/misc/lkdtm_core.c b/drivers/misc/lkdtm_core.c
index 187cd9b63e9a..f212f865f9c6 100644
--- a/drivers/misc/lkdtm_core.c
+++ b/drivers/misc/lkdtm_core.c
@@ -111,7 +111,13 @@ 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,
};
static char* cp_name[] = {
@@ -154,7 +160,13 @@ 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",
};
static struct jprobe lkdtm;
@@ -166,6 +178,8 @@ 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 +188,9 @@ 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 +204,9 @@ 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 +400,213 @@ static void execute_user_location(void *dst)
func();
}
+static noinline unsigned char *do_usercopy_stack_callee(int value)
+{
+ unsigned char buf[32];
+ unsigned char *ptr = NULL;
+ int i;
+
+ /* Exercise stack to avoid everything living in registers. */
+ for (i = 0; i < sizeof(buf); i++) {
+ /*
+ * Hack to trick gcc into letting us return a reference
+ * to a local stack frame.
+ */
+ if (i == 0)
+ ptr = buf;
+ buf[i] = value & 0xff;
+ }
+
+ return ptr;
+}
+
+static noinline void do_usercopy_stack(bool to_user)
+{
+ 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. */
+ bad_stack = do_usercopy_stack_callee(alloc_size);
+
+ 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 {
+ 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 +905,24 @@ 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);
+ break;
+ case CT_USERCOPY_STACK_FRAME_FROM:
+ do_usercopy_stack(false);
+ break;
case CT_NONE:
default:
break;
@@ -971,6 +1215,11 @@ 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 +1271,8 @@ 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");
}
--
2.7.4
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