Branch data     Line data    Source code

       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                 :          0 : STATIC int INIT unxz(unsigned char *in, long in_size,
     252                 :            :                      long (*fill)(void *dest, unsigned long size),
     253                 :            :                      long (*flush)(void *src, unsigned long size),
     254                 :            :                      unsigned char *out, long *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                 :          0 :         if (in_used != NULL)
     267                 :          0 :                 *in_used = 0;
     268                 :            : 
     269                 :          0 :         if (fill == NULL && flush == NULL)
     270                 :          0 :                 s = xz_dec_init(XZ_SINGLE, 0);
     271                 :            :         else
     272                 :          0 :                 s = xz_dec_init(XZ_DYNALLOC, (uint32_t)-1);
     273                 :            : 
     274                 :          0 :         if (s == NULL)
     275                 :            :                 goto error_alloc_state;
     276                 :            : 
     277                 :          0 :         if (flush == NULL) {
     278                 :          0 :                 b.out = out;
     279                 :          0 :                 b.out_size = (size_t)-1;
     280                 :            :         } else {
     281                 :          0 :                 b.out_size = XZ_IOBUF_SIZE;
     282                 :          0 :                 b.out = malloc(XZ_IOBUF_SIZE);
     283                 :          0 :                 if (b.out == NULL)
     284                 :            :                         goto error_alloc_out;
     285                 :            :         }
     286                 :            : 
     287                 :          0 :         if (in == NULL) {
     288                 :            :                 must_free_in = true;
     289                 :            :                 in = malloc(XZ_IOBUF_SIZE);
     290                 :          0 :                 if (in == NULL)
     291                 :            :                         goto error_alloc_in;
     292                 :            :         }
     293                 :            : 
     294                 :          0 :         b.in = in;
     295                 :          0 :         b.in_pos = 0;
     296                 :          0 :         b.in_size = in_size;
     297                 :          0 :         b.out_pos = 0;
     298                 :            : 
     299                 :          0 :         if (fill == NULL && flush == NULL) {
     300                 :          0 :                 ret = xz_dec_run(s, &b);
     301                 :            :         } else {
     302                 :            :                 do {
     303                 :          0 :                         if (b.in_pos == b.in_size && fill != NULL) {
     304                 :          0 :                                 if (in_used != NULL)
     305                 :          0 :                                         *in_used += b.in_pos;
     306                 :            : 
     307                 :          0 :                                 b.in_pos = 0;
     308                 :            : 
     309                 :          0 :                                 in_size = fill(in, XZ_IOBUF_SIZE);
     310                 :          0 :                                 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                 :          0 :                                 b.in_size = in_size;
     321                 :            :                         }
     322                 :            : 
     323                 :          0 :                         ret = xz_dec_run(s, &b);
     324                 :            : 
     325                 :          0 :                         if (flush != NULL && (b.out_pos == b.out_size
     326                 :          0 :                                         || (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                 :          0 :                                 if (flush(b.out, b.out_pos) != (long)b.out_pos)
     333                 :            :                                         ret = XZ_BUF_ERROR;
     334                 :            : 
     335                 :          0 :                                 b.out_pos = 0;
     336                 :            :                         }
     337                 :          0 :                 } while (ret == XZ_OK);
     338                 :            : 
     339                 :          0 :                 if (must_free_in)
     340                 :          0 :                         free(in);
     341                 :            : 
     342                 :          0 :                 if (flush != NULL)
     343                 :          0 :                         free(b.out);
     344                 :            :         }
     345                 :            : 
     346                 :          0 :         if (in_used != NULL)
     347                 :          0 :                 *in_used += b.in_pos;
     348                 :            : 
     349                 :          0 :         xz_dec_end(s);
     350                 :            : 
     351                 :          0 :         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                 :          0 :                 error("XZ decompressor ran out of memory");
     358                 :          0 :                 break;
     359                 :            : 
     360                 :            :         case XZ_FORMAT_ERROR:
     361                 :          0 :                 error("Input is not in the XZ format (wrong magic bytes)");
     362                 :          0 :                 break;
     363                 :            : 
     364                 :            :         case XZ_OPTIONS_ERROR:
     365                 :          0 :                 error("Input was encoded with settings that are not "
     366                 :            :                                 "supported by this XZ decoder");
     367                 :          0 :                 break;
     368                 :            : 
     369                 :            :         case XZ_DATA_ERROR:
     370                 :            :         case XZ_BUF_ERROR:
     371                 :          0 :                 error("XZ-compressed data is corrupt");
     372                 :          0 :                 break;
     373                 :            : 
     374                 :            :         default:
     375                 :          0 :                 error("Bug in the XZ decompressor");
     376                 :          0 :                 break;
     377                 :            :         }
     378                 :            : 
     379                 :            :         return -1;
     380                 :            : 
     381                 :            : error_alloc_in:
     382                 :          0 :         if (flush != NULL)
     383                 :          0 :                 free(b.out);
     384                 :            : 
     385                 :            : error_alloc_out:
     386                 :          0 :         xz_dec_end(s);
     387                 :            : 
     388                 :            : error_alloc_state:
     389                 :          0 :         error("XZ decompressor ran out of memory");
     390                 :          0 :         return -1;
     391                 :            : }
     392                 :            : 
     393                 :            : /*
     394                 :            :  * This macro is used by architecture-specific files to decompress
     395                 :            :  * the kernel image.
     396                 :            :  */
     397                 :            : #ifdef XZ_PREBOOT
     398                 :            : STATIC int INIT __decompress(unsigned char *buf, long len,
     399                 :            :                            long (*fill)(void*, unsigned long),
     400                 :            :                            long (*flush)(void*, unsigned long),
     401                 :            :                            unsigned char *out_buf, long olen,
     402                 :            :                            long *pos,
     403                 :            :                            void (*error)(char *x))
     404                 :            : {
     405                 :            :         return unxz(buf, len, fill, flush, out_buf, pos, error);
     406                 :            : }
     407                 :            : #endif