/*
   * 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
  #	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
   * 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
  
  #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, int in_size,
  		     int (*fill)(void *dest, unsigned int size),
  		     int (*flush)(void *src, unsigned int size),
  		     unsigned char *out, int *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) != (int)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 unxz