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 /*
  * 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
  * incompressible. Thus, we must look for worst-case expansion when the
  * compressor is encoding incompressible data.
  *
  * The structure of the .xz file in case of a compressed 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 incompressible 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
 #   include <linux/slab.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
 #   define XZ_DEC_ARM
 #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
  * memmove speed can matter and only if there is a lot of incompressible data
  * (LZMA2 stores incompressible 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
 
 #ifndef memmove
 /* Not static to avoid a conflict with the prototype in the Linux headers. */
 void *memmove(void *dest, const void *src, size_t size)
 {
     uint8_t *d = dest;
     const uint8_t *s = src;
     size_t i;
 
     if (d < s) {
         for (i = 0; i < size; ++i)
             d[i] = s[i];
     } else if (d > s) {
         i = size;
         while (i-- > 0)
             d[i] = s[i];
     }
 
     return dest;
 }
 #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 INIT 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.
  */
 #ifdef XZ_PREBOOT
 STATIC int INIT __decompress(unsigned char *buf, long len,
                long (*fill)(void*, unsigned long),
                long (*flush)(void*, unsigned long),
                unsigned char *out_buf, long olen,
                long *pos,
                void (*error)(char *x))
 {
     return unxz(buf, len, fill, flush, out_buf, pos, error);
 }
 #endif

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