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![Kees Cook](/assets/img/avatar_default.png)
The hardened usercopy is now consistently avoiding checks against const sizes, since we really only want to perform runtime bounds checking on lengths that weren't known at build time. To test the hardened usercopy code, we must force the length arguments to be seen as non-const. Signed-off-by: Kees Cook <keescook@chromium.org>
322 lines
8.1 KiB
C
322 lines
8.1 KiB
C
/*
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* This is for all the tests related to copy_to_user() and copy_from_user()
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* hardening.
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*/
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#include "lkdtm.h"
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#include <linux/slab.h>
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#include <linux/vmalloc.h>
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#include <linux/mman.h>
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#include <linux/uaccess.h>
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#include <asm/cacheflush.h>
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/*
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* Many of the tests here end up using const sizes, but those would
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* normally be ignored by hardened usercopy, so force the compiler
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* into choosing the non-const path to make sure we trigger the
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* hardened usercopy checks by added "unconst" to all the const copies,
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* and making sure "cache_size" isn't optimized into a const.
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*/
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static volatile size_t unconst = 0;
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static volatile size_t cache_size = 1024;
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static struct kmem_cache *bad_cache;
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static const unsigned char test_text[] = "This is a test.\n";
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/*
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* Instead of adding -Wno-return-local-addr, just pass the stack address
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* through a function to obfuscate it from the compiler.
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*/
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static noinline unsigned char *trick_compiler(unsigned char *stack)
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{
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return stack + 0;
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}
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static noinline unsigned char *do_usercopy_stack_callee(int value)
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{
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unsigned char buf[32];
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int i;
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/* Exercise stack to avoid everything living in registers. */
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for (i = 0; i < sizeof(buf); i++) {
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buf[i] = value & 0xff;
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}
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return trick_compiler(buf);
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}
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static noinline void do_usercopy_stack(bool to_user, bool bad_frame)
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{
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unsigned long user_addr;
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unsigned char good_stack[32];
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unsigned char *bad_stack;
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int i;
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/* Exercise stack to avoid everything living in registers. */
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for (i = 0; i < sizeof(good_stack); i++)
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good_stack[i] = test_text[i % sizeof(test_text)];
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/* This is a pointer to outside our current stack frame. */
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if (bad_frame) {
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bad_stack = do_usercopy_stack_callee((uintptr_t)&bad_stack);
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} else {
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/* Put start address just inside stack. */
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bad_stack = task_stack_page(current) + THREAD_SIZE;
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bad_stack -= sizeof(unsigned long);
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}
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user_addr = vm_mmap(NULL, 0, PAGE_SIZE,
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PROT_READ | PROT_WRITE | PROT_EXEC,
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MAP_ANONYMOUS | MAP_PRIVATE, 0);
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if (user_addr >= TASK_SIZE) {
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pr_warn("Failed to allocate user memory\n");
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return;
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}
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if (to_user) {
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pr_info("attempting good copy_to_user of local stack\n");
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if (copy_to_user((void __user *)user_addr, good_stack,
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unconst + sizeof(good_stack))) {
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pr_warn("copy_to_user failed unexpectedly?!\n");
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goto free_user;
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}
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pr_info("attempting bad copy_to_user of distant stack\n");
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if (copy_to_user((void __user *)user_addr, bad_stack,
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unconst + sizeof(good_stack))) {
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pr_warn("copy_to_user failed, but lacked Oops\n");
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goto free_user;
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}
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} else {
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/*
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* There isn't a safe way to not be protected by usercopy
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* if we're going to write to another thread's stack.
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*/
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if (!bad_frame)
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goto free_user;
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pr_info("attempting good copy_from_user of local stack\n");
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if (copy_from_user(good_stack, (void __user *)user_addr,
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unconst + sizeof(good_stack))) {
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pr_warn("copy_from_user failed unexpectedly?!\n");
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goto free_user;
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}
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pr_info("attempting bad copy_from_user of distant stack\n");
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if (copy_from_user(bad_stack, (void __user *)user_addr,
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unconst + sizeof(good_stack))) {
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pr_warn("copy_from_user failed, but lacked Oops\n");
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goto free_user;
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}
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}
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free_user:
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vm_munmap(user_addr, PAGE_SIZE);
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}
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static void do_usercopy_heap_size(bool to_user)
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{
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unsigned long user_addr;
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unsigned char *one, *two;
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size_t size = unconst + 1024;
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one = kmalloc(size, GFP_KERNEL);
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two = kmalloc(size, GFP_KERNEL);
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if (!one || !two) {
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pr_warn("Failed to allocate kernel memory\n");
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goto free_kernel;
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}
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user_addr = vm_mmap(NULL, 0, PAGE_SIZE,
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PROT_READ | PROT_WRITE | PROT_EXEC,
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MAP_ANONYMOUS | MAP_PRIVATE, 0);
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if (user_addr >= TASK_SIZE) {
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pr_warn("Failed to allocate user memory\n");
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goto free_kernel;
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}
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memset(one, 'A', size);
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memset(two, 'B', size);
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if (to_user) {
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pr_info("attempting good copy_to_user of correct size\n");
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if (copy_to_user((void __user *)user_addr, one, size)) {
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pr_warn("copy_to_user failed unexpectedly?!\n");
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goto free_user;
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}
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pr_info("attempting bad copy_to_user of too large size\n");
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if (copy_to_user((void __user *)user_addr, one, 2 * size)) {
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pr_warn("copy_to_user failed, but lacked Oops\n");
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goto free_user;
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}
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} else {
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pr_info("attempting good copy_from_user of correct size\n");
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if (copy_from_user(one, (void __user *)user_addr, size)) {
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pr_warn("copy_from_user failed unexpectedly?!\n");
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goto free_user;
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}
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pr_info("attempting bad copy_from_user of too large size\n");
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if (copy_from_user(one, (void __user *)user_addr, 2 * size)) {
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pr_warn("copy_from_user failed, but lacked Oops\n");
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goto free_user;
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}
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}
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free_user:
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vm_munmap(user_addr, PAGE_SIZE);
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free_kernel:
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kfree(one);
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kfree(two);
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}
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static void do_usercopy_heap_flag(bool to_user)
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{
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unsigned long user_addr;
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unsigned char *good_buf = NULL;
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unsigned char *bad_buf = NULL;
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/* Make sure cache was prepared. */
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if (!bad_cache) {
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pr_warn("Failed to allocate kernel cache\n");
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return;
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}
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/*
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* Allocate one buffer from each cache (kmalloc will have the
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* SLAB_USERCOPY flag already, but "bad_cache" won't).
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*/
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good_buf = kmalloc(cache_size, GFP_KERNEL);
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bad_buf = kmem_cache_alloc(bad_cache, GFP_KERNEL);
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if (!good_buf || !bad_buf) {
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pr_warn("Failed to allocate buffers from caches\n");
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goto free_alloc;
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}
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/* Allocate user memory we'll poke at. */
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user_addr = vm_mmap(NULL, 0, PAGE_SIZE,
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PROT_READ | PROT_WRITE | PROT_EXEC,
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MAP_ANONYMOUS | MAP_PRIVATE, 0);
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if (user_addr >= TASK_SIZE) {
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pr_warn("Failed to allocate user memory\n");
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goto free_alloc;
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}
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memset(good_buf, 'A', cache_size);
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memset(bad_buf, 'B', cache_size);
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if (to_user) {
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pr_info("attempting good copy_to_user with SLAB_USERCOPY\n");
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if (copy_to_user((void __user *)user_addr, good_buf,
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cache_size)) {
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pr_warn("copy_to_user failed unexpectedly?!\n");
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goto free_user;
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}
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pr_info("attempting bad copy_to_user w/o SLAB_USERCOPY\n");
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if (copy_to_user((void __user *)user_addr, bad_buf,
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cache_size)) {
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pr_warn("copy_to_user failed, but lacked Oops\n");
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goto free_user;
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}
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} else {
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pr_info("attempting good copy_from_user with SLAB_USERCOPY\n");
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if (copy_from_user(good_buf, (void __user *)user_addr,
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cache_size)) {
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pr_warn("copy_from_user failed unexpectedly?!\n");
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goto free_user;
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}
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pr_info("attempting bad copy_from_user w/o SLAB_USERCOPY\n");
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if (copy_from_user(bad_buf, (void __user *)user_addr,
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cache_size)) {
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pr_warn("copy_from_user failed, but lacked Oops\n");
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goto free_user;
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}
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}
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free_user:
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vm_munmap(user_addr, PAGE_SIZE);
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free_alloc:
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if (bad_buf)
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kmem_cache_free(bad_cache, bad_buf);
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kfree(good_buf);
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}
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/* Callable tests. */
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void lkdtm_USERCOPY_HEAP_SIZE_TO(void)
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{
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do_usercopy_heap_size(true);
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}
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void lkdtm_USERCOPY_HEAP_SIZE_FROM(void)
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{
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do_usercopy_heap_size(false);
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}
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void lkdtm_USERCOPY_HEAP_FLAG_TO(void)
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{
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do_usercopy_heap_flag(true);
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}
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void lkdtm_USERCOPY_HEAP_FLAG_FROM(void)
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{
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do_usercopy_heap_flag(false);
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}
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void lkdtm_USERCOPY_STACK_FRAME_TO(void)
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{
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do_usercopy_stack(true, true);
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}
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void lkdtm_USERCOPY_STACK_FRAME_FROM(void)
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{
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do_usercopy_stack(false, true);
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}
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void lkdtm_USERCOPY_STACK_BEYOND(void)
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{
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do_usercopy_stack(true, false);
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}
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void lkdtm_USERCOPY_KERNEL(void)
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{
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unsigned long user_addr;
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user_addr = vm_mmap(NULL, 0, PAGE_SIZE,
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PROT_READ | PROT_WRITE | PROT_EXEC,
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MAP_ANONYMOUS | MAP_PRIVATE, 0);
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if (user_addr >= TASK_SIZE) {
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pr_warn("Failed to allocate user memory\n");
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return;
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}
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pr_info("attempting good copy_to_user from kernel rodata\n");
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if (copy_to_user((void __user *)user_addr, test_text,
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unconst + sizeof(test_text))) {
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pr_warn("copy_to_user failed unexpectedly?!\n");
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goto free_user;
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}
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pr_info("attempting bad copy_to_user from kernel text\n");
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if (copy_to_user((void __user *)user_addr, vm_mmap,
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unconst + PAGE_SIZE)) {
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pr_warn("copy_to_user failed, but lacked Oops\n");
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goto free_user;
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}
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free_user:
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vm_munmap(user_addr, PAGE_SIZE);
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}
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void __init lkdtm_usercopy_init(void)
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{
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/* Prepare cache that lacks SLAB_USERCOPY flag. */
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bad_cache = kmem_cache_create("lkdtm-no-usercopy", cache_size, 0,
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0, NULL);
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}
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void __exit lkdtm_usercopy_exit(void)
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{
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kmem_cache_destroy(bad_cache);
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}
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