drivers/misc/lkdtm_perms.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * This is for all the tests related to validating kernel memory
   4  * permissions: non-executable regions, non-writable regions, and
   5  * even non-readable regions.
   6  */
   7 #include "lkdtm.h"
   8 #include <linux/slab.h>
   9 #include <linux/vmalloc.h>
  10 #include <linux/mman.h>
  11 #include <linux/uaccess.h>
  12 #include <asm/cacheflush.h>
  13
  14 /* Whether or not to fill the target memory area with do_nothing(). */
  15 #define CODE_WRITE      true
  16 #define CODE_AS_IS      false
  17
  18 /* How many bytes to copy to be sure we've copied enough of do_nothing(). */
  19 #define EXEC_SIZE 64
  20
  21 /* This is non-const, so it will end up in the .data section. */
  22 static u8 data_area[EXEC_SIZE];
  23
  24 /* This is cost, so it will end up in the .rodata section. */
  25 static const unsigned long rodata = 0xAA55AA55;
  26
  27 /* This is marked __ro_after_init, so it should ultimately be .rodata. */
  28 static unsigned long ro_after_init __ro_after_init = 0x55AA5500;
  29
  30 /*
  31  * This just returns to the caller. It is designed to be copied into
  32  * non-executable memory regions.
  33  */
  34 static void do_nothing(void)
  35 {
  36         return;
  37 }
  38
  39 /* Must immediately follow do_nothing for size calculuations to work out. */
  40 static void do_overwritten(void)
  41 {
  42         pr_info("do_overwritten wasn't overwritten!\n");
  43         return;
  44 }
  45
  46 static noinline void execute_location(void *dst, bool write)
  47 {
  48         void (*func)(void) = dst;
  49
  50         pr_info("attempting ok execution at %p\n", do_nothing);
  51         do_nothing();
  52
  53         if (write == CODE_WRITE) {
  54                 memcpy(dst, do_nothing, EXEC_SIZE);
  55                 flush_icache_range((unsigned long)dst,
  56                                    (unsigned long)dst + EXEC_SIZE);
  57         }
  58         pr_info("attempting bad execution at %p\n", func);
  59         func();
  60 }
  61
  62 static void execute_user_location(void *dst)
  63 {
  64         int copied;
  65
  66         /* Intentionally crossing kernel/user memory boundary. */
  67         void (*func)(void) = dst;
  68
  69         pr_info("attempting ok execution at %p\n", do_nothing);
  70         do_nothing();
  71
  72         copied = access_process_vm(current, (unsigned long)dst, do_nothing,
  73                                    EXEC_SIZE, FOLL_WRITE);
  74         if (copied < EXEC_SIZE)
  75                 return;
  76         pr_info("attempting bad execution at %p\n", func);
  77         func();
  78 }
  79
  80 void lkdtm_WRITE_RO(void)
  81 {
  82         /* Explicitly cast away "const" for the test. */
  83         unsigned long *ptr = (unsigned long *)&rodata;
  84
  85         pr_info("attempting bad rodata write at %p\n", ptr);
  86         *ptr ^= 0xabcd1234;
  87 }
  88
  89 void lkdtm_WRITE_RO_AFTER_INIT(void)
  90 {
  91         unsigned long *ptr = &ro_after_init;
  92
  93         /*
  94          * Verify we were written to during init. Since an Oops
  95          * is considered a "success", a failure is to just skip the
  96          * real test.
  97          */
  98         if ((*ptr & 0xAA) != 0xAA) {
  99                 pr_info("%p was NOT written during init!?\n", ptr);
 100                 return;
 101         }
 102
 103         pr_info("attempting bad ro_after_init write at %p\n", ptr);
 104         *ptr ^= 0xabcd1234;
 105 }
 106
 107 void lkdtm_WRITE_KERN(void)
 108 {
 109         size_t size;
 110         unsigned char *ptr;
 111
 112         size = (unsigned long)do_overwritten - (unsigned long)do_nothing;
 113         ptr = (unsigned char *)do_overwritten;
 114
 115         pr_info("attempting bad %zu byte write at %p\n", size, ptr);
 116         memcpy(ptr, (unsigned char *)do_nothing, size);
 117         flush_icache_range((unsigned long)ptr, (unsigned long)(ptr + size));
 118
 119         do_overwritten();
 120 }
 121
 122 void lkdtm_EXEC_DATA(void)
 123 {
 124         execute_location(data_area, CODE_WRITE);
 125 }
 126
 127 void lkdtm_EXEC_STACK(void)
 128 {
 129         u8 stack_area[EXEC_SIZE];
 130         execute_location(stack_area, CODE_WRITE);
 131 }
 132
 133 void lkdtm_EXEC_KMALLOC(void)
 134 {
 135         u32 *kmalloc_area = kmalloc(EXEC_SIZE, GFP_KERNEL);
 136         execute_location(kmalloc_area, CODE_WRITE);
 137         kfree(kmalloc_area);
 138 }
 139
 140 void lkdtm_EXEC_VMALLOC(void)
 141 {
 142         u32 *vmalloc_area = vmalloc(EXEC_SIZE);
 143         execute_location(vmalloc_area, CODE_WRITE);
 144         vfree(vmalloc_area);
 145 }
 146
 147 void lkdtm_EXEC_RODATA(void)
 148 {
 149         execute_location(lkdtm_rodata_do_nothing, CODE_AS_IS);
 150 }
 151
 152 void lkdtm_EXEC_USERSPACE(void)
 153 {
 154         unsigned long user_addr;
 155
 156         user_addr = vm_mmap(NULL, 0, PAGE_SIZE,
 157                             PROT_READ | PROT_WRITE | PROT_EXEC,
 158                             MAP_ANONYMOUS | MAP_PRIVATE, 0);
 159         if (user_addr >= TASK_SIZE) {
 160                 pr_warn("Failed to allocate user memory\n");
 161                 return;
 162         }
 163         execute_user_location((void *)user_addr);
 164         vm_munmap(user_addr, PAGE_SIZE);
 165 }
 166
 167 void lkdtm_ACCESS_USERSPACE(void)
 168 {
 169         unsigned long user_addr, tmp = 0;
 170         unsigned long *ptr;
 171
 172         user_addr = vm_mmap(NULL, 0, PAGE_SIZE,
 173                             PROT_READ | PROT_WRITE | PROT_EXEC,
 174                             MAP_ANONYMOUS | MAP_PRIVATE, 0);
 175         if (user_addr >= TASK_SIZE) {
 176                 pr_warn("Failed to allocate user memory\n");
 177                 return;
 178         }
 179
 180         if (copy_to_user((void __user *)user_addr, &tmp, sizeof(tmp))) {
 181                 pr_warn("copy_to_user failed\n");
 182                 vm_munmap(user_addr, PAGE_SIZE);
 183                 return;
 184         }
 185
 186         ptr = (unsigned long *)user_addr;
 187
 188         pr_info("attempting bad read at %p\n", ptr);
 189         tmp = *ptr;
 190         tmp += 0xc0dec0de;
 191
 192         pr_info("attempting bad write at %p\n", ptr);
 193         *ptr = tmp;
 194
 195         vm_munmap(user_addr, PAGE_SIZE);
 196 }
 197
 198 void __init lkdtm_perms_init(void)
 199 {
 200         /* Make sure we can write to __ro_after_init values during __init */
 201         ro_after_init |= 0xAA;
 202
 203 }