tools/testing/selftests/vm/mremap_dontunmap.c

   1 // SPDX-License-Identifier: GPL-2.0
   2
   3 /*
   4  * Tests for mremap w/ MREMAP_DONTUNMAP.
   5  *
   6  * Copyright 2020, Brian Geffon <bgeffon@google.com>
   7  */
   8 #define _GNU_SOURCE
   9 #include <sys/mman.h>
  10 #include <errno.h>
  11 #include <stdio.h>
  12 #include <stdlib.h>
  13 #include <string.h>
  14 #include <unistd.h>
  15
  16 #include "../kselftest.h"
  17
  18 #ifndef MREMAP_DONTUNMAP
  19 #define MREMAP_DONTUNMAP 4
  20 #endif
  21
  22 unsigned long page_size;
  23 char *page_buffer;
  24
  25 static void dump_maps(void)
  26 {
  27         char cmd[32];
  28
  29         snprintf(cmd, sizeof(cmd), "cat /proc/%d/maps", getpid());
  30         system(cmd);
  31 }
  32
  33 #define BUG_ON(condition, description)                                        \
  34         do {                                                                  \
  35                 if (condition) {                                              \
  36                         fprintf(stderr, "[FAIL]\t%s():%d\t%s:%s\n", __func__, \
  37                                 __LINE__, (description), strerror(errno));    \
  38                         dump_maps();                                      \
  39                         exit(1);                                              \
  40                 }                                                             \
  41         } while (0)
  42
  43 // Try a simple operation for to "test" for kernel support this prevents
  44 // reporting tests as failed when it's run on an older kernel.
  45 static int kernel_support_for_mremap_dontunmap()
  46 {
  47         int ret = 0;
  48         unsigned long num_pages = 1;
  49         void *source_mapping = mmap(NULL, num_pages * page_size, PROT_NONE,
  50                                     MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
  51         BUG_ON(source_mapping == MAP_FAILED, "mmap");
  52
  53         // This simple remap should only fail if MREMAP_DONTUNMAP isn't
  54         // supported.
  55         void *dest_mapping =
  56             mremap(source_mapping, num_pages * page_size, num_pages * page_size,
  57                    MREMAP_DONTUNMAP | MREMAP_MAYMOVE, 0);
  58         if (dest_mapping == MAP_FAILED) {
  59                 ret = errno;
  60         } else {
  61                 BUG_ON(munmap(dest_mapping, num_pages * page_size) == -1,
  62                        "unable to unmap destination mapping");
  63         }
  64
  65         BUG_ON(munmap(source_mapping, num_pages * page_size) == -1,
  66                "unable to unmap source mapping");
  67         return ret;
  68 }
  69
  70 // This helper will just validate that an entire mapping contains the expected
  71 // byte.
  72 static int check_region_contains_byte(void *addr, unsigned long size, char byte)
  73 {
  74         BUG_ON(size & (page_size - 1),
  75                "check_region_contains_byte expects page multiples");
  76         BUG_ON((unsigned long)addr & (page_size - 1),
  77                "check_region_contains_byte expects page alignment");
  78
  79         memset(page_buffer, byte, page_size);
  80
  81         unsigned long num_pages = size / page_size;
  82         unsigned long i;
  83
  84         // Compare each page checking that it contains our expected byte.
  85         for (i = 0; i < num_pages; ++i) {
  86                 int ret =
  87                     memcmp(addr + (i * page_size), page_buffer, page_size);
  88                 if (ret) {
  89                         return ret;
  90                 }
  91         }
  92
  93         return 0;
  94 }
  95
  96 // this test validates that MREMAP_DONTUNMAP moves the pagetables while leaving
  97 // the source mapping mapped.
  98 static void mremap_dontunmap_simple()
  99 {
 100         unsigned long num_pages = 5;
 101
 102         void *source_mapping =
 103             mmap(NULL, num_pages * page_size, PROT_READ | PROT_WRITE,
 104                  MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
 105         BUG_ON(source_mapping == MAP_FAILED, "mmap");
 106
 107         memset(source_mapping, 'a', num_pages * page_size);
 108
 109         // Try to just move the whole mapping anywhere (not fixed).
 110         void *dest_mapping =
 111             mremap(source_mapping, num_pages * page_size, num_pages * page_size,
 112                    MREMAP_DONTUNMAP | MREMAP_MAYMOVE, NULL);
 113         BUG_ON(dest_mapping == MAP_FAILED, "mremap");
 114
 115         // Validate that the pages have been moved, we know they were moved if
 116         // the dest_mapping contains a's.
 117         BUG_ON(check_region_contains_byte
 118                (dest_mapping, num_pages * page_size, 'a') != 0,
 119                "pages did not migrate");
 120         BUG_ON(check_region_contains_byte
 121                (source_mapping, num_pages * page_size, 0) != 0,
 122                "source should have no ptes");
 123
 124         BUG_ON(munmap(dest_mapping, num_pages * page_size) == -1,
 125                "unable to unmap destination mapping");
 126         BUG_ON(munmap(source_mapping, num_pages * page_size) == -1,
 127                "unable to unmap source mapping");
 128 }
 129
 130 // This test validates MREMAP_DONTUNMAP will move page tables to a specific
 131 // destination using MREMAP_FIXED, also while validating that the source
 132 // remains intact.
 133 static void mremap_dontunmap_simple_fixed()
 134 {
 135         unsigned long num_pages = 5;
 136
 137         // Since we want to guarantee that we can remap to a point, we will
 138         // create a mapping up front.
 139         void *dest_mapping =
 140             mmap(NULL, num_pages * page_size, PROT_READ | PROT_WRITE,
 141                  MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
 142         BUG_ON(dest_mapping == MAP_FAILED, "mmap");
 143         memset(dest_mapping, 'X', num_pages * page_size);
 144
 145         void *source_mapping =
 146             mmap(NULL, num_pages * page_size, PROT_READ | PROT_WRITE,
 147                  MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
 148         BUG_ON(source_mapping == MAP_FAILED, "mmap");
 149         memset(source_mapping, 'a', num_pages * page_size);
 150
 151         void *remapped_mapping =
 152             mremap(source_mapping, num_pages * page_size, num_pages * page_size,
 153                    MREMAP_FIXED | MREMAP_DONTUNMAP | MREMAP_MAYMOVE,
 154                    dest_mapping);
 155         BUG_ON(remapped_mapping == MAP_FAILED, "mremap");
 156         BUG_ON(remapped_mapping != dest_mapping,
 157                "mremap should have placed the remapped mapping at dest_mapping");
 158
 159         // The dest mapping will have been unmap by mremap so we expect the Xs
 160         // to be gone and replaced with a's.
 161         BUG_ON(check_region_contains_byte
 162                (dest_mapping, num_pages * page_size, 'a') != 0,
 163                "pages did not migrate");
 164
 165         // And the source mapping will have had its ptes dropped.
 166         BUG_ON(check_region_contains_byte
 167                (source_mapping, num_pages * page_size, 0) != 0,
 168                "source should have no ptes");
 169
 170         BUG_ON(munmap(dest_mapping, num_pages * page_size) == -1,
 171                "unable to unmap destination mapping");
 172         BUG_ON(munmap(source_mapping, num_pages * page_size) == -1,
 173                "unable to unmap source mapping");
 174 }
 175
 176 // This test validates that we can MREMAP_DONTUNMAP for a portion of an
 177 // existing mapping.
 178 static void mremap_dontunmap_partial_mapping()
 179 {
 180         /*
 181          *  source mapping:
 182          *  --------------
 183          *  | aaaaaaaaaa |
 184          *  --------------
 185          *  to become:
 186          *  --------------
 187          *  | aaaaa00000 |
 188          *  --------------
 189          *  With the destination mapping containing 5 pages of As.
 190          *  ---------
 191          *  | aaaaa |
 192          *  ---------
 193          */
 194         unsigned long num_pages = 10;
 195         void *source_mapping =
 196             mmap(NULL, num_pages * page_size, PROT_READ | PROT_WRITE,
 197                  MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
 198         BUG_ON(source_mapping == MAP_FAILED, "mmap");
 199         memset(source_mapping, 'a', num_pages * page_size);
 200
 201         // We will grab the last 5 pages of the source and move them.
 202         void *dest_mapping =
 203             mremap(source_mapping + (5 * page_size), 5 * page_size,
 204                    5 * page_size,
 205                    MREMAP_DONTUNMAP | MREMAP_MAYMOVE, NULL);
 206         BUG_ON(dest_mapping == MAP_FAILED, "mremap");
 207
 208         // We expect the first 5 pages of the source to contain a's and the
 209         // final 5 pages to contain zeros.
 210         BUG_ON(check_region_contains_byte(source_mapping, 5 * page_size, 'a') !=
 211                0, "first 5 pages of source should have original pages");
 212         BUG_ON(check_region_contains_byte
 213                (source_mapping + (5 * page_size), 5 * page_size, 0) != 0,
 214                "final 5 pages of source should have no ptes");
 215
 216         // Finally we expect the destination to have 5 pages worth of a's.
 217         BUG_ON(check_region_contains_byte(dest_mapping, 5 * page_size, 'a') !=
 218                0, "dest mapping should contain ptes from the source");
 219
 220         BUG_ON(munmap(dest_mapping, 5 * page_size) == -1,
 221                "unable to unmap destination mapping");
 222         BUG_ON(munmap(source_mapping, num_pages * page_size) == -1,
 223                "unable to unmap source mapping");
 224 }
 225
 226 // This test validates that we can remap over only a portion of a mapping.
 227 static void mremap_dontunmap_partial_mapping_overwrite(void)
 228 {
 229         /*
 230          *  source mapping:
 231          *  ---------
 232          *  |aaaaa|
 233          *  ---------
 234          *  dest mapping initially:
 235          *  -----------
 236          *  |XXXXXXXXXX|
 237          *  ------------
 238          *  Source to become:
 239          *  ---------
 240          *  |00000|
 241          *  ---------
 242          *  With the destination mapping containing 5 pages of As.
 243          *  ------------
 244          *  |aaaaaXXXXX|
 245          *  ------------
 246          */
 247         void *source_mapping =
 248             mmap(NULL, 5 * page_size, PROT_READ | PROT_WRITE,
 249                  MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
 250         BUG_ON(source_mapping == MAP_FAILED, "mmap");
 251         memset(source_mapping, 'a', 5 * page_size);
 252
 253         void *dest_mapping =
 254             mmap(NULL, 10 * page_size, PROT_READ | PROT_WRITE,
 255                  MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
 256         BUG_ON(dest_mapping == MAP_FAILED, "mmap");
 257         memset(dest_mapping, 'X', 10 * page_size);
 258
 259         // We will grab the last 5 pages of the source and move them.
 260         void *remapped_mapping =
 261             mremap(source_mapping, 5 * page_size,
 262                    5 * page_size,
 263                    MREMAP_DONTUNMAP | MREMAP_MAYMOVE | MREMAP_FIXED, dest_mapping);
 264         BUG_ON(dest_mapping == MAP_FAILED, "mremap");
 265         BUG_ON(dest_mapping != remapped_mapping, "expected to remap to dest_mapping");
 266
 267         BUG_ON(check_region_contains_byte(source_mapping, 5 * page_size, 0) !=
 268                0, "first 5 pages of source should have no ptes");
 269
 270         // Finally we expect the destination to have 5 pages worth of a's.
 271         BUG_ON(check_region_contains_byte(dest_mapping, 5 * page_size, 'a') != 0,
 272                         "dest mapping should contain ptes from the source");
 273
 274         // Finally the last 5 pages shouldn't have been touched.
 275         BUG_ON(check_region_contains_byte(dest_mapping + (5 * page_size),
 276                                 5 * page_size, 'X') != 0,
 277                         "dest mapping should have retained the last 5 pages");
 278
 279         BUG_ON(munmap(dest_mapping, 10 * page_size) == -1,
 280                "unable to unmap destination mapping");
 281         BUG_ON(munmap(source_mapping, 5 * page_size) == -1,
 282                "unable to unmap source mapping");
 283 }
 284
 285 int main(void)
 286 {
 287         page_size = sysconf(_SC_PAGE_SIZE);
 288
 289         // test for kernel support for MREMAP_DONTUNMAP skipping the test if
 290         // not.
 291         if (kernel_support_for_mremap_dontunmap() != 0) {
 292                 printf("No kernel support for MREMAP_DONTUNMAP\n");
 293                 return KSFT_SKIP;
 294         }
 295
 296         // Keep a page sized buffer around for when we need it.
 297         page_buffer =
 298             mmap(NULL, page_size, PROT_READ | PROT_WRITE,
 299                  MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
 300         BUG_ON(page_buffer == MAP_FAILED, "unable to mmap a page.");
 301
 302         mremap_dontunmap_simple();
 303         mremap_dontunmap_simple_fixed();
 304         mremap_dontunmap_partial_mapping();
 305         mremap_dontunmap_partial_mapping_overwrite();
 306
 307         BUG_ON(munmap(page_buffer, page_size) == -1,
 308                "unable to unmap page buffer");
 309
 310         printf("OK\n");
 311         return 0;
 312 }