// SPDX-License-Identifier: GPL-2.0
/*
 * This is for all the tests related to copy_to_user() and copy_from_user()
 * hardening.
 */
#include "lkdtm.h"
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/sched/task_stack.h>
#include <linux/mman.h>
#include <linux/uaccess.h>
#include <asm/cacheflush.h>

/*
 * Many of the tests here end up using const sizes, but those would
 * normally be ignored by hardened usercopy, so force the compiler
 * into choosing the non-const path to make sure we trigger the
 * hardened usercopy checks by added "unconst" to all the const copies,
 * and making sure "cache_size" isn't optimized into a const.
 */
static volatile size_t unconst;
static volatile size_t cache_size = 1024;
static struct kmem_cache *whitelist_cache;

static const unsigned char test_text[] = "This is a test.\n";

/*
 * 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((uintptr_t)&bad_stack);
        } 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,
                                 unconst + 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,
                                 unconst + 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,
                                   unconst + 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,
                                   unconst + sizeof(good_stack))) {
                        pr_warn("copy_from_user failed, but lacked Oops\n");
                        goto free_user;
                }
        }

free_user:
        vm_munmap(user_addr, PAGE_SIZE);
}

/*
 * This checks for whole-object size validation with hardened usercopy,
 * with or without usercopy whitelisting.
 */
static void do_usercopy_heap_size(bool to_user)
{
        unsigned long user_addr;
        unsigned char *one, *two;
        void __user *test_user_addr;
        void *test_kern_addr;
        size_t size = unconst + 1024;

        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);

        test_user_addr = (void __user *)(user_addr + 16);
        test_kern_addr = one + 16;

        if (to_user) {
                pr_info("attempting good copy_to_user of correct size\n");
                if (copy_to_user(test_user_addr, test_kern_addr, size / 2)) {
                        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(test_user_addr, test_kern_addr, 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(test_kern_addr, test_user_addr, size / 2)) {
                        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(test_kern_addr, test_user_addr, 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);
}

/*
 * This checks for the specific whitelist window within an object. If this
 * test passes, then do_usercopy_heap_size() tests will pass too.
 */
static void do_usercopy_heap_whitelist(bool to_user)
{
        unsigned long user_alloc;
        unsigned char *buf = NULL;
        unsigned char __user *user_addr;
        size_t offset, size;

        /* Make sure cache was prepared. */
        if (!whitelist_cache) {
                pr_warn("Failed to allocate kernel cache\n");
                return;
        }

        /*
         * Allocate a buffer with a whitelisted window in the buffer.
         */
        buf = kmem_cache_alloc(whitelist_cache, GFP_KERNEL);
        if (!buf) {
                pr_warn("Failed to allocate buffer from whitelist cache\n");
                goto free_alloc;
        }

        /* Allocate user memory we'll poke at. */
        user_alloc = vm_mmap(NULL, 0, PAGE_SIZE,
                            PROT_READ | PROT_WRITE | PROT_EXEC,
                            MAP_ANONYMOUS | MAP_PRIVATE, 0);
        if (user_alloc >= TASK_SIZE) {
                pr_warn("Failed to allocate user memory\n");
                goto free_alloc;
        }
        user_addr = (void __user *)user_alloc;

        memset(buf, 'B', cache_size);

        /* Whitelisted window in buffer, from kmem_cache_create_usercopy. */
        offset = (cache_size / 4) + unconst;
        size = (cache_size / 16) + unconst;

        if (to_user) {
                pr_info("attempting good copy_to_user inside whitelist\n");
                if (copy_to_user(user_addr, buf + offset, size)) {
                        pr_warn("copy_to_user failed unexpectedly?!\n");
                        goto free_user;
                }

                pr_info("attempting bad copy_to_user outside whitelist\n");
                if (copy_to_user(user_addr, buf + offset - 1, size)) {
                        pr_warn("copy_to_user failed, but lacked Oops\n");
                        goto free_user;
                }
        } else {
                pr_info("attempting good copy_from_user inside whitelist\n");
                if (copy_from_user(buf + offset, user_addr, size)) {
                        pr_warn("copy_from_user failed unexpectedly?!\n");
                        goto free_user;
                }

                pr_info("attempting bad copy_from_user outside whitelist\n");
                if (copy_from_user(buf + offset - 1, user_addr, size)) {
                        pr_warn("copy_from_user failed, but lacked Oops\n");
                        goto free_user;
                }
        }

free_user:
        vm_munmap(user_alloc, PAGE_SIZE);
free_alloc:
        if (buf)
                kmem_cache_free(whitelist_cache, buf);
}

/* Callable tests. */
void lkdtm_USERCOPY_HEAP_SIZE_TO(void)
{
        do_usercopy_heap_size(true);
}

void lkdtm_USERCOPY_HEAP_SIZE_FROM(void)
{
        do_usercopy_heap_size(false);
}

void lkdtm_USERCOPY_HEAP_WHITELIST_TO(void)
{
        do_usercopy_heap_whitelist(true);
}

void lkdtm_USERCOPY_HEAP_WHITELIST_FROM(void)
{
        do_usercopy_heap_whitelist(false);
}

void lkdtm_USERCOPY_STACK_FRAME_TO(void)
{
        do_usercopy_stack(true, true);
}

void lkdtm_USERCOPY_STACK_FRAME_FROM(void)
{
        do_usercopy_stack(false, true);
}

void lkdtm_USERCOPY_STACK_BEYOND(void)
{
        do_usercopy_stack(true, false);
}

void lkdtm_USERCOPY_KERNEL(void)
{
        unsigned long user_addr;

        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;
        }

        pr_info("attempting good copy_to_user from kernel rodata\n");
        if (copy_to_user((void __user *)user_addr, test_text,
                         unconst + sizeof(test_text))) {
                pr_warn("copy_to_user failed unexpectedly?!\n");
                goto free_user;
        }

        pr_info("attempting bad copy_to_user from kernel text\n");
        if (copy_to_user((void __user *)user_addr, vm_mmap,
                         unconst + PAGE_SIZE)) {
                pr_warn("copy_to_user failed, but lacked Oops\n");
                goto free_user;
        }

free_user:
        vm_munmap(user_addr, PAGE_SIZE);
}

void lkdtm_USERCOPY_KERNEL_DS(void)
{
        char __user *user_ptr =
                (char __user *)(0xFUL << (sizeof(unsigned long) * 8 - 4));
        mm_segment_t old_fs = get_fs();
        char buf[10] = {0};

        pr_info("attempting copy_to_user() to noncanonical address: %px\n",
                user_ptr);
        set_fs(KERNEL_DS);
        if (copy_to_user(user_ptr, buf, sizeof(buf)) == 0)
                pr_err("copy_to_user() to noncanonical address succeeded!?\n");
        set_fs(old_fs);
}

void __init lkdtm_usercopy_init(void)
{
        /* Prepare cache that lacks SLAB_USERCOPY flag. */
        whitelist_cache =
                kmem_cache_create_usercopy("lkdtm-usercopy", cache_size,
                                           0, 0,
                                           cache_size / 4,
                                           cache_size / 16,
                                           NULL);
}

void __exit lkdtm_usercopy_exit(void)
{
        kmem_cache_destroy(whitelist_cache);
}