lib/decompress_unxz.c

   1 /*
   2  * Wrapper for decompressing XZ-compressed kernel, initramfs, and initrd
   3  *
   4  * Author: Lasse Collin <lasse.collin@tukaani.org>
   5  *
   6  * This file has been put into the public domain.
   7  * You can do whatever you want with this file.
   8  */
   9
  10 /*
  11  * Important notes about in-place decompression
  12  *
  13  * At least on x86, the kernel is decompressed in place: the compressed data
  14  * is placed to the end of the output buffer, and the decompressor overwrites
  15  * most of the compressed data. There must be enough safety margin to
  16  * guarantee that the write position is always behind the read position.
  17  *
  18  * The safety margin for XZ with LZMA2 or BCJ+LZMA2 is calculated below.
  19  * Note that the margin with XZ is bigger than with Deflate (gzip)!
  20  *
  21  * The worst case for in-place decompression is that the beginning of
  22  * the file is compressed extremely well, and the rest of the file is
  23  * uncompressible. Thus, we must look for worst-case expansion when the
  24  * compressor is encoding uncompressible data.
  25  *
  26  * The structure of the .xz file in case of a compresed kernel is as follows.
  27  * Sizes (as bytes) of the fields are in parenthesis.
  28  *
  29  *    Stream Header (12)
  30  *    Block Header:
  31  *      Block Header (8-12)
  32  *      Compressed Data (N)
  33  *      Block Padding (0-3)
  34  *      CRC32 (4)
  35  *    Index (8-20)
  36  *    Stream Footer (12)
  37  *
  38  * Normally there is exactly one Block, but let's assume that there are
  39  * 2-4 Blocks just in case. Because Stream Header and also Block Header
  40  * of the first Block don't make the decompressor produce any uncompressed
  41  * data, we can ignore them from our calculations. Block Headers of possible
  42  * additional Blocks have to be taken into account still. With these
  43  * assumptions, it is safe to assume that the total header overhead is
  44  * less than 128 bytes.
  45  *
  46  * Compressed Data contains LZMA2 or BCJ+LZMA2 encoded data. Since BCJ
  47  * doesn't change the size of the data, it is enough to calculate the
  48  * safety margin for LZMA2.
  49  *
  50  * LZMA2 stores the data in chunks. Each chunk has a header whose size is
  51  * a maximum of 6 bytes, but to get round 2^n numbers, let's assume that
  52  * the maximum chunk header size is 8 bytes. After the chunk header, there
  53  * may be up to 64 KiB of actual payload in the chunk. Often the payload is
  54  * quite a bit smaller though; to be safe, let's assume that an average
  55  * chunk has only 32 KiB of payload.
  56  *
  57  * The maximum uncompressed size of the payload is 2 MiB. The minimum
  58  * uncompressed size of the payload is in practice never less than the
  59  * payload size itself. The LZMA2 format would allow uncompressed size
  60  * to be less than the payload size, but no sane compressor creates such
  61  * files. LZMA2 supports storing uncompressible data in uncompressed form,
  62  * so there's never a need to create payloads whose uncompressed size is
  63  * smaller than the compressed size.
  64  *
  65  * The assumption, that the uncompressed size of the payload is never
  66  * smaller than the payload itself, is valid only when talking about
  67  * the payload as a whole. It is possible that the payload has parts where
  68  * the decompressor consumes more input than it produces output. Calculating
  69  * the worst case for this would be tricky. Instead of trying to do that,
  70  * let's simply make sure that the decompressor never overwrites any bytes
  71  * of the payload which it is currently reading.
  72  *
  73  * Now we have enough information to calculate the safety margin. We need
  74  *   - 128 bytes for the .xz file format headers;
  75  *   - 8 bytes per every 32 KiB of uncompressed size (one LZMA2 chunk header
  76  *     per chunk, each chunk having average payload size of 32 KiB); and
  77  *   - 64 KiB (biggest possible LZMA2 chunk payload size) to make sure that
  78  *     the decompressor never overwrites anything from the LZMA2 chunk
  79  *     payload it is currently reading.
  80  *
  81  * We get the following formula:
  82  *
  83  *    safety_margin = 128 + uncompressed_size * 8 / 32768 + 65536
  84  *                  = 128 + (uncompressed_size >> 12) + 65536
  85  *
  86  * For comparison, according to arch/x86/boot/compressed/misc.c, the
  87  * equivalent formula for Deflate is this:
  88  *
  89  *    safety_margin = 18 + (uncompressed_size >> 12) + 32768
  90  *
  91  * Thus, when updating Deflate-only in-place kernel decompressor to
  92  * support XZ, the fixed overhead has to be increased from 18+32768 bytes
  93  * to 128+65536 bytes.
  94  */
  95
  96 /*
  97  * STATIC is defined to "static" if we are being built for kernel
  98  * decompression (pre-boot code). <linux/decompress/mm.h> will define
  99  * STATIC to empty if it wasn't already defined. Since we will need to
 100  * know later if we are being used for kernel decompression, we define
 101  * XZ_PREBOOT here.
 102  */
 103 #ifdef STATIC
 104 #       define XZ_PREBOOT
 105 #endif
 106 #ifdef __KERNEL__
 107 #       include <linux/decompress/mm.h>
 108 #endif
 109 #define XZ_EXTERN STATIC
 110
 111 #ifndef XZ_PREBOOT
 112 #       include <linux/slab.h>
 113 #       include <linux/xz.h>
 114 #else
 115 /*
 116  * Use the internal CRC32 code instead of kernel's CRC32 module, which
 117  * is not available in early phase of booting.
 118  */
 119 #define XZ_INTERNAL_CRC32 1
 120
 121 /*
 122  * For boot time use, we enable only the BCJ filter of the current
 123  * architecture or none if no BCJ filter is available for the architecture.
 124  */
 125 #ifdef CONFIG_X86
 126 #       define XZ_DEC_X86
 127 #endif
 128 #ifdef CONFIG_PPC
 129 #       define XZ_DEC_POWERPC
 130 #endif
 131 #ifdef CONFIG_ARM
 132 #       define XZ_DEC_ARM
 133 #endif
 134 #ifdef CONFIG_IA64
 135 #       define XZ_DEC_IA64
 136 #endif
 137 #ifdef CONFIG_SPARC
 138 #       define XZ_DEC_SPARC
 139 #endif
 140
 141 /*
 142  * This will get the basic headers so that memeq() and others
 143  * can be defined.
 144  */
 145 #include "xz/xz_private.h"
 146
 147 /*
 148  * Replace the normal allocation functions with the versions from
 149  * <linux/decompress/mm.h>. vfree() needs to support vfree(NULL)
 150  * when XZ_DYNALLOC is used, but the pre-boot free() doesn't support it.
 151  * Workaround it here because the other decompressors don't need it.
 152  */
 153 #undef kmalloc
 154 #undef kfree
 155 #undef vmalloc
 156 #undef vfree
 157 #define kmalloc(size, flags) malloc(size)
 158 #define kfree(ptr) free(ptr)
 159 #define vmalloc(size) malloc(size)
 160 #define vfree(ptr) do { if (ptr != NULL) free(ptr); } while (0)
 161
 162 /*
 163  * FIXME: Not all basic memory functions are provided in architecture-specific
 164  * files (yet). We define our own versions here for now, but this should be
 165  * only a temporary solution.
 166  *
 167  * memeq and memzero are not used much and any remotely sane implementation
 168  * is fast enough. memcpy/memmove speed matters in multi-call mode, but
 169  * the kernel image is decompressed in single-call mode, in which only
 170  * memcpy speed can matter and only if there is a lot of uncompressible data
 171  * (LZMA2 stores uncompressible chunks in uncompressed form). Thus, the
 172  * functions below should just be kept small; it's probably not worth
 173  * optimizing for speed.
 174  */
 175
 176 #ifndef memeq
 177 static bool memeq(const void *a, const void *b, size_t size)
 178 {
 179         const uint8_t *x = a;
 180         const uint8_t *y = b;
 181         size_t i;
 182
 183         for (i = 0; i < size; ++i)
 184                 if (x[i] != y[i])
 185                         return false;
 186
 187         return true;
 188 }
 189 #endif
 190
 191 #ifndef memzero
 192 static void memzero(void *buf, size_t size)
 193 {
 194         uint8_t *b = buf;
 195         uint8_t *e = b + size;
 196
 197         while (b != e)
 198                 *b++ = '\0';
 199 }
 200 #endif
 201
 202 #ifndef memmove
 203 /* Not static to avoid a conflict with the prototype in the Linux headers. */
 204 void *memmove(void *dest, const void *src, size_t size)
 205 {
 206         uint8_t *d = dest;
 207         const uint8_t *s = src;
 208         size_t i;
 209
 210         if (d < s) {
 211                 for (i = 0; i < size; ++i)
 212                         d[i] = s[i];
 213         } else if (d > s) {
 214                 i = size;
 215                 while (i-- > 0)
 216                         d[i] = s[i];
 217         }
 218
 219         return dest;
 220 }
 221 #endif
 222
 223 /*
 224  * Since we need memmove anyway, would use it as memcpy too.
 225  * Commented out for now to avoid breaking things.
 226  */
 227 /*
 228 #ifndef memcpy
 229 #       define memcpy memmove
 230 #endif
 231 */
 232
 233 #include "xz/xz_crc32.c"
 234 #include "xz/xz_dec_stream.c"
 235 #include "xz/xz_dec_lzma2.c"
 236 #include "xz/xz_dec_bcj.c"
 237
 238 #endif /* XZ_PREBOOT */
 239
 240 /* Size of the input and output buffers in multi-call mode */
 241 #define XZ_IOBUF_SIZE 4096
 242
 243 /*
 244  * This function implements the API defined in <linux/decompress/generic.h>.
 245  *
 246  * This wrapper will automatically choose single-call or multi-call mode
 247  * of the native XZ decoder API. The single-call mode can be used only when
 248  * both input and output buffers are available as a single chunk, i.e. when
 249  * fill() and flush() won't be used.
 250  */
 251 STATIC int INIT unxz(unsigned char *in, int in_size,
 252                      int (*fill)(void *dest, unsigned int size),
 253                      int (*flush)(void *src, unsigned int size),
 254                      unsigned char *out, int *in_used,
 255                      void (*error)(char *x))
 256 {
 257         struct xz_buf b;
 258         struct xz_dec *s;
 259         enum xz_ret ret;
 260         bool must_free_in = false;
 261
 262 #if XZ_INTERNAL_CRC32
 263         xz_crc32_init();
 264 #endif
 265
 266         if (in_used != NULL)
 267                 *in_used = 0;
 268
 269         if (fill == NULL && flush == NULL)
 270                 s = xz_dec_init(XZ_SINGLE, 0);
 271         else
 272                 s = xz_dec_init(XZ_DYNALLOC, (uint32_t)-1);
 273
 274         if (s == NULL)
 275                 goto error_alloc_state;
 276
 277         if (flush == NULL) {
 278                 b.out = out;
 279                 b.out_size = (size_t)-1;
 280         } else {
 281                 b.out_size = XZ_IOBUF_SIZE;
 282                 b.out = malloc(XZ_IOBUF_SIZE);
 283                 if (b.out == NULL)
 284                         goto error_alloc_out;
 285         }
 286
 287         if (in == NULL) {
 288                 must_free_in = true;
 289                 in = malloc(XZ_IOBUF_SIZE);
 290                 if (in == NULL)
 291                         goto error_alloc_in;
 292         }
 293
 294         b.in = in;
 295         b.in_pos = 0;
 296         b.in_size = in_size;
 297         b.out_pos = 0;
 298
 299         if (fill == NULL && flush == NULL) {
 300                 ret = xz_dec_run(s, &b);
 301         } else {
 302                 do {
 303                         if (b.in_pos == b.in_size && fill != NULL) {
 304                                 if (in_used != NULL)
 305                                         *in_used += b.in_pos;
 306
 307                                 b.in_pos = 0;
 308
 309                                 in_size = fill(in, XZ_IOBUF_SIZE);
 310                                 if (in_size < 0) {
 311                                         /*
 312                                          * This isn't an optimal error code
 313                                          * but it probably isn't worth making
 314                                          * a new one either.
 315                                          */
 316                                         ret = XZ_BUF_ERROR;
 317                                         break;
 318                                 }
 319
 320                                 b.in_size = in_size;
 321                         }
 322
 323                         ret = xz_dec_run(s, &b);
 324
 325                         if (flush != NULL && (b.out_pos == b.out_size
 326                                         || (ret != XZ_OK && b.out_pos > 0))) {
 327                                 /*
 328                                  * Setting ret here may hide an error
 329                                  * returned by xz_dec_run(), but probably
 330                                  * it's not too bad.
 331                                  */
 332                                 if (flush(b.out, b.out_pos) != (int)b.out_pos)
 333                                         ret = XZ_BUF_ERROR;
 334
 335                                 b.out_pos = 0;
 336                         }
 337                 } while (ret == XZ_OK);
 338
 339                 if (must_free_in)
 340                         free(in);
 341
 342                 if (flush != NULL)
 343                         free(b.out);
 344         }
 345
 346         if (in_used != NULL)
 347                 *in_used += b.in_pos;
 348
 349         xz_dec_end(s);
 350
 351         switch (ret) {
 352         case XZ_STREAM_END:
 353                 return 0;
 354
 355         case XZ_MEM_ERROR:
 356                 /* This can occur only in multi-call mode. */
 357                 error("XZ decompressor ran out of memory");
 358                 break;
 359
 360         case XZ_FORMAT_ERROR:
 361                 error("Input is not in the XZ format (wrong magic bytes)");
 362                 break;
 363
 364         case XZ_OPTIONS_ERROR:
 365                 error("Input was encoded with settings that are not "
 366                                 "supported by this XZ decoder");
 367                 break;
 368
 369         case XZ_DATA_ERROR:
 370         case XZ_BUF_ERROR:
 371                 error("XZ-compressed data is corrupt");
 372                 break;
 373
 374         default:
 375                 error("Bug in the XZ decompressor");
 376                 break;
 377         }
 378
 379         return -1;
 380
 381 error_alloc_in:
 382         if (flush != NULL)
 383                 free(b.out);
 384
 385 error_alloc_out:
 386         xz_dec_end(s);
 387
 388 error_alloc_state:
 389         error("XZ decompressor ran out of memory");
 390         return -1;
 391 }
 392
 393 /*
 394  * This macro is used by architecture-specific files to decompress
 395  * the kernel image.
 396  */
 397 #define decompress unxz