/*

 * Wrapper for decompressing XZ-compressed kernel, initramfs, and initrd

 *

 * Author: Lasse Collin <lasse.collin@tukaani.org>

 *

 * This file has been put into the public domain.

 * You can do whatever you want with this file.

 */

/*

 * Important notes about in-place decompression

 *

 * At least on x86, the kernel is decompressed in place: the compressed data

 * is placed to the end of the output buffer, and the decompressor overwrites

 * most of the compressed data. There must be enough safety margin to

 * guarantee that the write position is always behind the read position.

 *

 * The safety margin for XZ with LZMA2 or BCJ+LZMA2 is calculated below.

 * Note that the margin with XZ is bigger than with Deflate (gzip)!

 *

 * The worst case for in-place decompression is that the beginning of

 * the file is compressed extremely well, and the rest of the file is

 * uncompressible. Thus, we must look for worst-case expansion when the

 * compressor is encoding uncompressible data.

 *

 * The structure of the .xz file in case of a compresed kernel is as follows.

 * Sizes (as bytes) of the fields are in parenthesis.

 *

 *    Stream Header (12)

 *    Block Header:

 *      Block Header (8-12)

 *      Compressed Data (N)

 *      Block Padding (0-3)

 *      CRC32 (4)

 *    Index (8-20)

 *    Stream Footer (12)

 *

 * Normally there is exactly one Block, but let's assume that there are

 * 2-4 Blocks just in case. Because Stream Header and also Block Header

 * of the first Block don't make the decompressor produce any uncompressed

 * data, we can ignore them from our calculations. Block Headers of possible

 * additional Blocks have to be taken into account still. With these

 * assumptions, it is safe to assume that the total header overhead is

 * less than 128 bytes.

 *

 * Compressed Data contains LZMA2 or BCJ+LZMA2 encoded data. Since BCJ

 * doesn't change the size of the data, it is enough to calculate the

 * safety margin for LZMA2.

 *

 * LZMA2 stores the data in chunks. Each chunk has a header whose size is

 * a maximum of 6 bytes, but to get round 2^n numbers, let's assume that

 * the maximum chunk header size is 8 bytes. After the chunk header, there

 * may be up to 64 KiB of actual payload in the chunk. Often the payload is

 * quite a bit smaller though; to be safe, let's assume that an average

 * chunk has only 32 KiB of payload.

 *

 * The maximum uncompressed size of the payload is 2 MiB. The minimum

 * uncompressed size of the payload is in practice never less than the

 * payload size itself. The LZMA2 format would allow uncompressed size

 * to be less than the payload size, but no sane compressor creates such

 * files. LZMA2 supports storing uncompressible data in uncompressed form,

 * so there's never a need to create payloads whose uncompressed size is

 * smaller than the compressed size.

 *

 * The assumption, that the uncompressed size of the payload is never

 * smaller than the payload itself, is valid only when talking about

 * the payload as a whole. It is possible that the payload has parts where

 * the decompressor consumes more input than it produces output. Calculating

 * the worst case for this would be tricky. Instead of trying to do that,

 * let's simply make sure that the decompressor never overwrites any bytes

 * of the payload which it is currently reading.

 *

 * Now we have enough information to calculate the safety margin. We need

 *   - 128 bytes for the .xz file format headers;

 *   - 8 bytes per every 32 KiB of uncompressed size (one LZMA2 chunk header

 *     per chunk, each chunk having average payload size of 32 KiB); and

 *   - 64 KiB (biggest possible LZMA2 chunk payload size) to make sure that

 *     the decompressor never overwrites anything from the LZMA2 chunk

 *     payload it is currently reading.

 *

 * We get the following formula:

 *

 *    safety_margin = 128 + uncompressed_size * 8 / 32768 + 65536

 *                  = 128 + (uncompressed_size >> 12) + 65536

 *

 * For comparison, according to arch/x86/boot/compressed/misc.c, the

 * equivalent formula for Deflate is this:

 *

 *    safety_margin = 18 + (uncompressed_size >> 12) + 32768

 *

 * Thus, when updating Deflate-only in-place kernel decompressor to

 * support XZ, the fixed overhead has to be increased from 18+32768 bytes

 * to 128+65536 bytes.

 */

/*

 * STATIC is defined to "static" if we are being built for kernel

 * decompression (pre-boot code). <linux/decompress/mm.h> will define

 * STATIC to empty if it wasn't already defined. Since we will need to

 * know later if we are being used for kernel decompression, we define

 * XZ_PREBOOT here.

 */

#ifdef STATIC

# define XZ_PREBOOT

#endif

#ifdef __KERNEL__

# include <linux/decompress/mm.h>

#endif

#define XZ_EXTERN STATIC

#ifndef XZ_PREBOOT

#define FREE free

#define MALLOC malloc

# include <malloc.h>

# include <linux/xz.h>

#else

/*

 * Use the internal CRC32 code instead of kernel's CRC32 module, which

 * is not available in early phase of booting.

 */

#define XZ_INTERNAL_CRC32 1

/*

 * For boot time use, we enable only the BCJ filter of the current

 * architecture or none if no BCJ filter is available for the architecture.

 */

#ifdef CONFIG_X86

# define XZ_DEC_X86

#endif

#ifdef CONFIG_PPC

# define XZ_DEC_POWERPC

#endif

#ifdef CONFIG_ARM

# ifdef CONFIG_ARM64

#   define XZ_DEC_ARM64

# elif defined CONFIG_THUMB2_BAREBOX

#   define XZ_DEC_ARMTHUMB

# else

#   define XZ_DEC_ARM

# endif

#endif

#ifdef CONFIG_IA64

# define XZ_DEC_IA64

#endif

#ifdef CONFIG_SPARC

# define XZ_DEC_SPARC

#endif

/*

 * This will get the basic headers so that memeq() and others

 * can be defined.

 */

#include "xz/xz_private.h"

/*

 * Replace the normal allocation functions with the versions from

 * <linux/decompress/mm.h>. vfree() needs to support vfree(NULL)

 * when XZ_DYNALLOC is used, but the pre-boot free() doesn't support it.

 * Workaround it here because the other decompressors don't need it.

 */

#undef kmalloc

#undef kfree

#undef vmalloc

#undef vfree

#define kmalloc(size, flags) malloc(size)

#define kfree(ptr) free(ptr)

#define vmalloc(size) malloc(size)

#define vfree(ptr) do { if (ptr != NULL) free(ptr); } while (0)

/*

 * FIXME: Not all basic memory functions are provided in architecture-specific

 * files (yet). We define our own versions here for now, but this should be

 * only a temporary solution.

 *

 * memeq and memzero are not used much and any remotely sane implementation

 * is fast enough. memcpy/memmove speed matters in multi-call mode, but

 * the kernel image is decompressed in single-call mode, in which only

 * memcpy speed can matter and only if there is a lot of uncompressible data

 * (LZMA2 stores uncompressible chunks in uncompressed form). Thus, the

 * functions below should just be kept small; it's probably not worth

 * optimizing for speed.

 */

#ifndef memeq

static bool memeq(const void *a, const void *b, size_t size)

{

  const uint8_t *x = a;

  const uint8_t *y = b;

  size_t i;

  for (i = 0; i < size; ++i)

    if (x[i] != y[i])

      return false;

  return true;

}

#endif

#ifndef memzero

static void memzero(void *buf, size_t size)

{

  uint8_t *b = buf;

  uint8_t *e = b + size;

  while (b != e)

    *b++ = '\0';

}

#endif

/*

 * Since we need memmove anyway, would use it as memcpy too.

 * Commented out for now to avoid breaking things.

 */

/*

#ifndef memcpy

# define memcpy memmove

#endif

*/

#include "xz/xz_crc32.c"

#include "xz/xz_dec_stream.c"

#include "xz/xz_dec_lzma2.c"

#include "xz/xz_dec_bcj.c"

#endif /* XZ_PREBOOT */

/* Size of the input and output buffers in multi-call mode */

#define XZ_IOBUF_SIZE 4096

/*

 * This function implements the API defined in <linux/decompress/generic.h>.

 *

 * This wrapper will automatically choose single-call or multi-call mode

 * of the native XZ decoder API. The single-call mode can be used only when

 * both input and output buffers are available as a single chunk, i.e. when

 * fill() and flush() won't be used.

 */

STATIC int decompress_unxz(unsigned char *in, long in_size,

         long (*fill)(void *dest, unsigned long size),

         long (*flush)(void *src, unsigned long size),

         unsigned char *out, long *in_used,

         void (*error)(char *x))

{

  struct xz_buf b;

  struct xz_dec *s;

  enum xz_ret ret;

  bool must_free_in = false;

#if XZ_INTERNAL_CRC32

  xz_crc32_init();

#endif

  if (in_used != NULL)

    *in_used = 0;

  if (fill == NULL && flush == NULL)

    s = xz_dec_init(XZ_SINGLE, 0);

  else

    s = xz_dec_init(XZ_DYNALLOC, (uint32_t)-1);

  if (s == NULL)

    goto error_alloc_state;

  if (flush == NULL) {

    b.out = out;

    b.out_size = (size_t)-1;

  } else {

    b.out_size = XZ_IOBUF_SIZE;

    b.out = MALLOC(XZ_IOBUF_SIZE);

    if (b.out == NULL)

      goto error_alloc_out;

  }

  if (in == NULL) {

    must_free_in = true;

    in = MALLOC(XZ_IOBUF_SIZE);

    if (in == NULL)

      goto error_alloc_in;

  }

  b.in = in;

  b.in_pos = 0;

  b.in_size = in_size;

  b.out_pos = 0;

  if (fill == NULL && flush == NULL) {

    ret = xz_dec_run(s, &b);

  } else {

    do {

      if (b.in_pos == b.in_size && fill != NULL) {

        if (in_used != NULL)

          *in_used += b.in_pos;

        b.in_pos = 0;

        in_size = fill(in, XZ_IOBUF_SIZE);

        if (in_size < 0) {

          /*

           * This isn't an optimal error code

           * but it probably isn't worth making

           * a new one either.

           */

          ret = XZ_BUF_ERROR;

          break;

        }

        b.in_size = in_size;

      }

      ret = xz_dec_run(s, &b);

      if (flush != NULL && (b.out_pos == b.out_size

          || (ret != XZ_OK && b.out_pos > 0))) {

        /*

         * Setting ret here may hide an error

         * returned by xz_dec_run(), but probably

         * it's not too bad.

         */

        if (flush(b.out, b.out_pos) != (long)b.out_pos)

          ret = XZ_BUF_ERROR;

        b.out_pos = 0;

      }

    } while (ret == XZ_OK);

    if (must_free_in)

      FREE(in);

    if (flush != NULL)

      FREE(b.out);

  }

  if (in_used != NULL)

    *in_used += b.in_pos;

  xz_dec_end(s);

  switch (ret) {

  case XZ_STREAM_END:

    return 0;

  case XZ_MEM_ERROR:

    /* This can occur only in multi-call mode. */

    error("XZ decompressor ran out of memory");

    break;

  case XZ_FORMAT_ERROR:

    error("Input is not in the XZ format (wrong magic bytes)");

    break;

  case XZ_OPTIONS_ERROR:

    error("Input was encoded with settings that are not "

        "supported by this XZ decoder");

    break;

  case XZ_DATA_ERROR:

  case XZ_BUF_ERROR:

    error("XZ-compressed data is corrupt");

    break;

  default:

    error("Bug in the XZ decompressor");

    break;

  }

  return -1;

error_alloc_in:

  if (flush != NULL)

    FREE(b.out);

error_alloc_out:

  xz_dec_end(s);

error_alloc_state:

  error("XZ decompressor ran out of memory");

  return -1;

}

/*

 * This macro is used by architecture-specific files to decompress

 * the kernel image.

 */

#define decompress decompress_unxz