![Kees Cook](/assets/img/avatar_default.png)
This updates the USERCOPY_HEAP_FLAG_* tests to USERCOPY_HEAP_WHITELIST_*, since the final form of usercopy whitelisting ended up using an offset/size window instead of the earlier proposed allocation flags. Signed-off-by: Kees Cook <keescook@chromium.org>
340 lines
8.7 KiB
C
340 lines
8.7 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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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/sched/task_stack.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 *whitelist_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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/*
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* This checks for whole-object size validation with hardened usercopy,
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* with or without usercopy whitelisting.
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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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void __user *test_user_addr;
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void *test_kern_addr;
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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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test_user_addr = (void __user *)(user_addr + 16);
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test_kern_addr = one + 16;
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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(test_user_addr, test_kern_addr, size / 2)) {
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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(test_user_addr, test_kern_addr, 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(test_kern_addr, test_user_addr, size / 2)) {
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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(test_kern_addr, test_user_addr, 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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/*
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* This checks for the specific whitelist window within an object. If this
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* test passes, then do_usercopy_heap_size() tests will pass too.
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*/
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static void do_usercopy_heap_whitelist(bool to_user)
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{
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unsigned long user_alloc;
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unsigned char *buf = NULL;
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unsigned char __user *user_addr;
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size_t offset, size;
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/* Make sure cache was prepared. */
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if (!whitelist_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 a buffer with a whitelisted window in the buffer.
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*/
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buf = kmem_cache_alloc(whitelist_cache, GFP_KERNEL);
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if (!buf) {
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pr_warn("Failed to allocate buffer from whitelist cache\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_alloc = 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_alloc >= 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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user_addr = (void __user *)user_alloc;
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memset(buf, 'B', cache_size);
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/* Whitelisted window in buffer, from kmem_cache_create_usercopy. */
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offset = (cache_size / 4) + unconst;
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size = (cache_size / 16) + unconst;
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if (to_user) {
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pr_info("attempting good copy_to_user inside whitelist\n");
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if (copy_to_user(user_addr, buf + offset, 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 outside whitelist\n");
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if (copy_to_user(user_addr, buf + offset - 1, 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 inside whitelist\n");
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if (copy_from_user(buf + offset, 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 outside whitelist\n");
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if (copy_from_user(buf + offset - 1, user_addr, 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_alloc, PAGE_SIZE);
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free_alloc:
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if (buf)
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kmem_cache_free(whitelist_cache, 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_WHITELIST_TO(void)
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{
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do_usercopy_heap_whitelist(true);
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}
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void lkdtm_USERCOPY_HEAP_WHITELIST_FROM(void)
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{
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do_usercopy_heap_whitelist(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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whitelist_cache =
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kmem_cache_create_usercopy("lkdtm-usercopy", cache_size,
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0, 0,
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cache_size / 4,
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cache_size / 16,
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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(whitelist_cache);
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}
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