// SPDX-License-Identifier: GPL-2.0-or-later
/*
* lzx_decompress.c - A decompressor for the LZX compression format, which can
* be used in "System Compressed" files. This is based on the code from wimlib.
* This code only supports a window size (dictionary size) of 32768 bytes, since
* this is the only size used in System Compression.
*
* Copyright (C) 2015 Eric Biggers
*/
#include "decompress_common.h"
#include "lib.h"
/* Number of literal byte values */
#define LZX_NUM_CHARS 256
/* The smallest and largest allowed match lengths */
#define LZX_MIN_MATCH_LEN 2
#define LZX_MAX_MATCH_LEN 257
/* Number of distinct match lengths that can be represented */
#define LZX_NUM_LENS (LZX_MAX_MATCH_LEN - LZX_MIN_MATCH_LEN + 1)
/* Number of match lengths for which no length symbol is required */
#define LZX_NUM_PRIMARY_LENS 7
#define LZX_NUM_LEN_HEADERS (LZX_NUM_PRIMARY_LENS + 1)
/* Valid values of the 3-bit block type field */
#define LZX_BLOCKTYPE_VERBATIM 1
#define LZX_BLOCKTYPE_ALIGNED 2
#define LZX_BLOCKTYPE_UNCOMPRESSED 3
/* Number of offset slots for a window size of 32768 */
#define LZX_NUM_OFFSET_SLOTS 30
/* Number of symbols in the main code for a window size of 32768 */
#define LZX_MAINCODE_NUM_SYMBOLS \
(LZX_NUM_CHARS + (LZX_NUM_OFFSET_SLOTS * LZX_NUM_LEN_HEADERS))
/* Number of symbols in the length code */
#define LZX_LENCODE_NUM_SYMBOLS (LZX_NUM_LENS - LZX_NUM_PRIMARY_LENS)
/* Number of symbols in the precode */
#define LZX_PRECODE_NUM_SYMBOLS 20
/* Number of bits in which each precode codeword length is represented */
#define LZX_PRECODE_ELEMENT_SIZE 4
/* Number of low-order bits of each match offset that are entropy-encoded in
* aligned offset blocks
*/
#define LZX_NUM_ALIGNED_OFFSET_BITS 3
/* Number of symbols in the aligned offset code */
#define LZX_ALIGNEDCODE_NUM_SYMBOLS (1 << LZX_NUM_ALIGNED_OFFSET_BITS)
/* Mask for the match offset bits that are entropy-encoded in aligned offset
* blocks
*/
#define LZX_ALIGNED_OFFSET_BITMASK ((1 << LZX_NUM_ALIGNED_OFFSET_BITS) - 1)
/* Number of bits in which each aligned offset codeword length is represented */
#define LZX_ALIGNEDCODE_ELEMENT_SIZE 3
/* Maximum lengths (in bits) of the codewords in each Huffman code */
#define LZX_MAX_MAIN_CODEWORD_LEN 16
#define LZX_MAX_LEN_CODEWORD_LEN 16
#define LZX_MAX_PRE_CODEWORD_LEN ((1 << LZX_PRECODE_ELEMENT_SIZE) - 1)
#define LZX_MAX_ALIGNED_CODEWORD_LEN ((1 << LZX_ALIGNEDCODE_ELEMENT_SIZE) - 1)
/* The default "filesize" value used in pre/post-processing. In the LZX format
* used in cabinet files this value must be given to the decompressor, whereas
* in the LZX format used in WIM files and system-compressed files this value is
* fixed at 12000000.
*/
#define LZX_DEFAULT_FILESIZE 12000000
/* Assumed block size when the encoded block size begins with a 0 bit. */
#define LZX_DEFAULT_BLOCK_SIZE 32768
/* Number of offsets in the recent (or "repeat") offsets queue. */
#define LZX_NUM_RECENT_OFFSETS 3
/* These values are chosen for fast decompression. */
#define LZX_MAINCODE_TABLEBITS 11
#define LZX_LENCODE_TABLEBITS 10
#define LZX_PRECODE_TABLEBITS 6
#define LZX_ALIGNEDCODE_TABLEBITS 7
#define LZX_READ_LENS_MAX_OVERRUN 50
/* Mapping: offset slot => first match offset that uses that offset slot.
*/
static const u32 lzx_offset_slot_base[LZX_NUM_OFFSET_SLOTS + 1] = {
0, 1, 2, 3, 4, /* 0 --- 4 */
6, 8, 12, 16, 24, /* 5 --- 9 */
32, 48, 64, 96, 128, /* 10 --- 14 */
192, 256, 384, 512, 768, /* 15 --- 19 */
1024, 1536, 2048, 3072, 4096, /* 20 --- 24 */
6144, 8192, 12288, 16384, 24576, /* 25 --- 29 */
32768, /* extra */
};
/* Mapping: offset slot => how many extra bits must be read and added to the
* corresponding offset slot base to decode the match offset.
*/
static const u8 lzx_extra_offset_bits[LZX_NUM_OFFSET_SLOTS] = {
0, 0, 0, 0, 1,
1, 2, 2, 3, 3,
4, 4, 5, 5, 6,
6, 7, 7, 8, 8,
9, 9, 10, 10, 11,
11, 12, 12, 13, 13,
};
/* Reusable heap-allocated memory for LZX decompression */
struct lzx_decompressor {
/* Huffman decoding tables, and arrays that map symbols to codeword
* lengths
*/
u16 maincode_decode_table[(1 << LZX_MAINCODE_TABLEBITS) +
(LZX_MAINCODE_NUM_SYMBOLS * 2)];
u8 maincode_lens[LZX_MAINCODE_NUM_SYMBOLS + LZX_READ_LENS_MAX_OVERRUN];
u16 lencode_decode_table[(1 << LZX_LENCODE_TABLEBITS) +
(LZX_LENCODE_NUM_SYMBOLS * 2)];
u8 lencode_lens[LZX_LENCODE_NUM_SYMBOLS + LZX_READ_LENS_MAX_OVERRUN];
u16 alignedcode_decode_table[(1 << LZX_ALIGNEDCODE_TABLEBITS) +
(LZX_ALIGNEDCODE_NUM_SYMBOLS * 2)];
u8 alignedcode_lens[LZX_ALIGNEDCODE_NUM_SYMBOLS];
u16 precode_decode_table[(1 << LZX_PRECODE_TABLEBITS) +
(LZX_PRECODE_NUM_SYMBOLS * 2)];
u8 precode_lens[LZX_PRECODE_NUM_SYMBOLS];
/* Temporary space for make_huffman_decode_table() */
u16 working_space[2 * (1 + LZX_MAX_MAIN_CODEWORD_LEN) +
LZX_MAINCODE_NUM_SYMBOLS];
};
static void undo_e8_translation(void *target, s32 input_pos)
{
s32 abs_offset, rel_offset;
abs_offset = get_unaligned_le32(target);
if (abs_offset >= 0) {
if (abs_offset < LZX_DEFAULT_FILESIZE) {
/* "good translation" */
rel_offset = abs_offset - input_pos;
put_unaligned_le32(rel_offset, target);
}
} else {
if (abs_offset >= -input_pos) {
/* "compensating translation" */
rel_offset = abs_offset + LZX_DEFAULT_FILESIZE;
put_unaligned_le32(rel_offset, target);
}
}
}
/*
* Undo the 'E8' preprocessing used in LZX. Before compression, the
* uncompressed data was preprocessed by changing the targets of suspected x86
* CALL instructions from relative offsets to absolute offsets. After
* match/literal decoding, the decompressor must undo the translation.
*/
static void lzx_postprocess(u8 *data, u32 size)
{
/*
* A worthwhile optimization is to push the end-of-buffer check into the
* relatively rare E8 case. This is possible if we replace the last six
* bytes of data with E8 bytes; then we are guaranteed to hit an E8 byte
* before reaching end-of-buffer. In addition, this scheme guarantees
* that no translation can begin following an E8 byte in the last 10
* bytes because a 4-byte offset containing E8 as its high byte is a
* large negative number that is not valid for translation. That is
* exactly what we need.
*/
u8 *tail;
u8 saved_bytes[6];
u8 *p;
if (size <= 10)
return;
tail = &data[size - 6];
memcpy(saved_bytes, tail, 6);
memset(tail, 0xE8, 6);
p = data;
for (;;) {
while (*p != 0xE8)
p++;
if (p >= tail)
break;
undo_e8_translation(p + 1, p - data);
p += 5;
}
memcpy(tail, saved_bytes, 6);
}
/* Read a Huffman-encoded symbol using the precode. */
static forceinline u32 read_presym(const struct lzx_decompressor *d,
struct input_bitstream *is)
{
return read_huffsym(is, d->precode_decode_table,
LZX_PRECODE_TABLEBITS, LZX_MAX_PRE_CODEWORD_LEN);
}
/* Read a Huffman-encoded symbol using the main code. */
static forceinline u32 read_mainsym(const struct lzx_decompressor *d,
struct input_bitstream *is)
{
return read_huffsym(is, d->maincode_decode_table,
LZX_MAINCODE_TABLEBITS, LZX_MAX_MAIN_CODEWORD_LEN);
}
/* Read a Huffman-encoded symbol using the length code. */
static forceinline u32 read_lensym(const struct lzx_decompressor *d,
struct input_bitstream *is)
{
return read_huffsym(is, d->lencode_decode_table,
LZX_LENCODE_TABLEBITS, LZX_MAX_LEN_CODEWORD_LEN);
}
/* Read a Huffman-encoded symbol using the aligned offset code. */
static forceinline u32 read_alignedsym(const struct lzx_decompressor *d,
struct input_bitstream *is)
{
return read_huffsym(is, d->alignedcode_decode_table,
LZX_ALIGNEDCODE_TABLEBITS,
LZX_MAX_ALIGNED_CODEWORD_LEN);
}
/*
* Read the precode from the compressed input bitstream, then use it to decode
* @num_lens codeword length values.
*
* @is: The input bitstream.
*
* @lens: An array that contains the length values from the previous time
* the codeword lengths for this Huffman code were read, or all 0's
* if this is the first time. This array must have at least
* (@num_lens + LZX_READ_LENS_MAX_OVERRUN) entries.
*
* @num_lens: Number of length values to decode.
*
* Returns 0 on success, or -1 if the data was invalid.
*/
static int lzx_read_codeword_lens(struct lzx_decompressor *d,
struct input_bitstream *is,
u8 *lens, u32 num_lens)
{
u8 *len_ptr = lens;
u8 *lens_end = lens + num_lens;
int i;
/* Read the lengths of the precode codewords. These are given
* explicitly.
*/
for (i = 0; i < LZX_PRECODE_NUM_SYMBOLS; i++) {
d->precode_lens[i] =
bitstream_read_bits(is, LZX_PRECODE_ELEMENT_SIZE);
}
/* Make the decoding table for the precode. */
if (make_huffman_decode_table(d->precode_decode_table,
LZX_PRECODE_NUM_SYMBOLS,
LZX_PRECODE_TABLEBITS,
d->precode_lens,
LZX_MAX_PRE_CODEWORD_LEN,
d->working_space))
return -1;
/* Decode the codeword lengths. */
do {
u32 presym;
u8 len;
/* Read the next precode symbol. */
presym = read_presym(d, is);
if (presym < 17) {
/* Difference from old length */
len = *len_ptr - presym;
if ((s8)len < 0)
len += 17;
*len_ptr++ = len;
} else {
/* Special RLE values */
u32 run_len;
if (presym == 17) {
/* Run of 0's */
run_len = 4 + bitstream_read_bits(is, 4);
len = 0;
} else if (presym == 18) {
/* Longer run of 0's */
run_len = 20 + bitstream_read_bits(is, 5);
len = 0;
} else {
/* Run of identical lengths */
run_len = 4 + bitstream_read_bits(is, 1);
presym = read_presym(d, is);
if (presym > 17)
return -1;
len = *len_ptr - presym;
if ((s8)len < 0)
len += 17;
}
do {
*len_ptr++ = len;
} while (--run_len);
/* Worst case overrun is when presym == 18,
* run_len == 20 + 31, and only 1 length was remaining.
* So LZX_READ_LENS_MAX_OVERRUN == 50.
*
* Overrun while reading the first half of maincode_lens
* can corrupt the previous values in the second half.
* This doesn't really matter because the resulting
* lengths will still be in range, and data that
* generates overruns is invalid anyway.
*/
}
} while (len_ptr < lens_end);
return 0;
}
/*
* Read the header of an LZX block and save the block type and (uncompressed)
* size in *block_type_ret and *block_size_ret, respectively.
*
* If the block is compressed, also update the Huffman decode @tables with the
* new Huffman codes. If the block is uncompressed, also update the match
* offset @queue with the new match offsets.
*
* Return 0 on success, or -1 if the data was invalid.
*/
static int lzx_read_block_header(struct lzx_decompressor *d,
struct input_bitstream *is,
int *block_type_ret,
u32 *block_size_ret,
u32 recent_offsets[])
{
int block_type;
u32 block_size;
int i;
bitstream_ensure_bits(is, 4);
/* The first three bits tell us what kind of block it is, and should be
* one of the LZX_BLOCKTYPE_* values.
*/
block_type = bitstream_pop_bits(is, 3);
/* Read the block size. */
if (bitstream_pop_bits(is, 1)) {
block_size = LZX_DEFAULT_BLOCK_SIZE;
} else {
block_size = 0;
block_size |= bitstream_read_bits(is, 8);
block_size <<= 8;
block_size |= bitstream_read_bits(is, 8);
}
switch (block_type) {
case LZX_BLOCKTYPE_ALIGNED:
/* Read the aligned offset code and prepare its decode table.
*/
for (i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++) {
d->alignedcode_lens[i] =
bitstream_read_bits(is,
LZX_ALIGNEDCODE_ELEMENT_SIZE);
}
if (make_huffman_decode_table(d->alignedcode_decode_table,
LZX_ALIGNEDCODE_NUM_SYMBOLS,
LZX_ALIGNEDCODE_TABLEBITS,
d->alignedcode_lens,
LZX_MAX_ALIGNED_CODEWORD_LEN,
d->working_space))
return -1;
/* Fall though, since the rest of the header for aligned offset
* blocks is the same as that for verbatim blocks.
*/
fallthrough;
case LZX_BLOCKTYPE_VERBATIM:
/* Read the main code and prepare its decode table.
*
* Note that the codeword lengths in the main code are encoded
* in two parts: one part for literal symbols, and one part for
* match symbols.
*/
if (lzx_read_codeword_lens(d, is, d->maincode_lens,
LZX_NUM_CHARS))
return -1;
if (lzx_read_codeword_lens(d, is,
d->maincode_lens + LZX_NUM_CHARS,
LZX_MAINCODE_NUM_SYMBOLS - LZX_NUM_CHARS))
return -1;
if (make_huffman_decode_table(d->maincode_decode_table,
LZX_MAINCODE_NUM_SYMBOLS,
LZX_MAINCODE_TABLEBITS,
d->maincode_lens,
LZX_MAX_MAIN_CODEWORD_LEN,
d->working_space))
return -1;
/* Read the length code and prepare its decode table. */
if (lzx_read_codeword_lens(d, is, d->lencode_lens,
LZX_LENCODE_NUM_SYMBOLS))
return -1;
if (make_huffman_decode_table(d->lencode_decode_table,
LZX_LENCODE_NUM_SYMBOLS,
LZX_LENCODE_TABLEBITS,
d->lencode_lens,
LZX_MAX_LEN_CODEWORD_LEN,
d->working_space))
return -1;
break;
case LZX_BLOCKTYPE_UNCOMPRESSED:
/* Before reading the three recent offsets from the uncompressed
* block header, the stream must be aligned on a 16-bit
* boundary. But if the stream is *already* aligned, then the
* next 16 bits must be discarded.
*/
bitstream_ensure_bits(is, 1);
bitstream_align(is);
recent_offsets[0] = bitstream_read_u32(is);
recent_offsets[1] = bitstream_read_u32(is);
recent_offsets[2] = bitstream_read_u32(is);
/* Offsets of 0 are invalid. */
if (recent_offsets[0] == 0 || recent_offsets[1] == 0 ||
recent_offsets[2] == 0)
return -1;
break;
default:
/* Unrecognized block type. */
return -1;
}
*block_type_ret = block_type;
*block_size_ret = block_size;
return 0;
}
/* Decompress a block of LZX-compressed data. */
static int lzx_decompress_block(const struct lzx_decompressor *d,
struct input_bitstream *is,
int block_type, u32 block_size,
u8 * const out_begin, u8 *out_next,
u32 recent_offsets[])
{
u8 * const block_end = out_next + block_size;
u32 ones_if_aligned = 0U - (block_type == LZX_BLOCKTYPE_ALIGNED);
do {
u32 mainsym;
u32 match_len;
u32 match_offset;
u32 offset_slot;
u32 num_extra_bits;
mainsym = read_mainsym(d, is);
if (mainsym < LZX_NUM_CHARS) {
/* Literal */
*out_next++ = mainsym;
continue;
}
/* Match */
/* Decode the length header and offset slot. */
mainsym -= LZX_NUM_CHARS;
match_len = mainsym % LZX_NUM_LEN_HEADERS;
offset_slot = mainsym / LZX_NUM_LEN_HEADERS;
/* If needed, read a length symbol to decode the full length. */
if (match_len == LZX_NUM_PRIMARY_LENS)
match_len += read_lensym(d, is);
match_len += LZX_MIN_MATCH_LEN;
if (offset_slot < LZX_NUM_RECENT_OFFSETS) {
/* Repeat offset */
/* Note: This isn't a real LRU queue, since using the R2
* offset doesn't bump the R1 offset down to R2. This
* quirk allows all 3 recent offsets to be handled by
* the same code. (For R0, the swap is a no-op.)
*/
match_offset = recent_offsets[offset_slot];
recent_offsets[offset_slot] = recent_offsets[0];
recent_offsets[0] = match_offset;
} else {
/* Explicit offset */
/* Look up the number of extra bits that need to be read
* to decode offsets with this offset slot.
*/
num_extra_bits = lzx_extra_offset_bits[offset_slot];
/* Start with the offset slot base value. */
match_offset = lzx_offset_slot_base[offset_slot];
/* In aligned offset blocks, the low-order 3 bits of
* each offset are encoded using the aligned offset
* code. Otherwise, all the extra bits are literal.
*/
if ((num_extra_bits & ones_if_aligned) >= LZX_NUM_ALIGNED_OFFSET_BITS) {
match_offset +=
bitstream_read_bits(is, num_extra_bits -
LZX_NUM_ALIGNED_OFFSET_BITS)
<< LZX_NUM_ALIGNED_OFFSET_BITS;
match_offset += read_alignedsym(d, is);
} else {
match_offset += bitstream_read_bits(is, num_extra_bits);
}
/* Adjust the offset. */
match_offset -= (LZX_NUM_RECENT_OFFSETS - 1);
/* Update the recent offsets. */
recent_offsets[2] = recent_offsets[1];
recent_offsets[1] = recent_offsets[0];
recent_offsets[0] = match_offset;
}
/* Validate the match, then copy it to the current position. */
if (match_len > (size_t)(block_end - out_next))
return -1;
if (match_offset > (size_t)(out_next - out_begin))
return -1;
out_next = lz_copy(out_next, match_len, match_offset,
block_end, LZX_MIN_MATCH_LEN);
} while (out_next != block_end);
return 0;
}
/*
* lzx_allocate_decompressor - Allocate an LZX decompressor
*
* Return the pointer to the decompressor on success, or return NULL and set
* errno on failure.
*/
struct lzx_decompressor *lzx_allocate_decompressor(void)
{
return kmalloc(sizeof(struct lzx_decompressor), GFP_NOFS);
}
/*
* lzx_decompress - Decompress a buffer of LZX-compressed data
*
* @decompressor: A decompressor allocated with lzx_allocate_decompressor()
* @compressed_data: The buffer of data to decompress
* @compressed_size: Number of bytes of compressed data
* @uncompressed_data: The buffer in which to store the decompressed data
* @uncompressed_size: The number of bytes the data decompresses into
*
* Return 0 on success, or return -1 and set errno on failure.
*/
int lzx_decompress(struct lzx_decompressor *decompressor,
const void *compressed_data, size_t compressed_size,
void *uncompressed_data, size_t uncompressed_size)
{
struct lzx_decompressor *d = decompressor;
u8 * const out_begin = uncompressed_data;
u8 *out_next = out_begin;
u8 * const out_end = out_begin + uncompressed_size;
struct input_bitstream is;
u32 recent_offsets[LZX_NUM_RECENT_OFFSETS] = {1, 1, 1};
int e8_status = 0;
init_input_bitstream(&is, compressed_data, compressed_size);
/* Codeword lengths begin as all 0's for delta encoding purposes. */
memset(d->maincode_lens, 0, LZX_MAINCODE_NUM_SYMBOLS);
memset(d->lencode_lens, 0, LZX_LENCODE_NUM_SYMBOLS);
/* Decompress blocks until we have all the uncompressed data. */
while (out_next != out_end) {
int block_type;
u32 block_size;
if (lzx_read_block_header(d, &is, &block_type, &block_size,
recent_offsets))
goto invalid;
if (block_size < 1 || block_size > (size_t)(out_end - out_next))
goto invalid;
if (block_type != LZX_BLOCKTYPE_UNCOMPRESSED) {
/* Compressed block */
if (lzx_decompress_block(d,
&is,
block_type,
block_size,
out_begin,
out_next,
recent_offsets))
goto invalid;
e8_status |= d->maincode_lens[0xe8];
out_next += block_size;
} else {
/* Uncompressed block */
out_next = bitstream_read_bytes(&is, out_next,
block_size);
if (!out_next)
goto invalid;
if (block_size & 1)
bitstream_read_byte(&is);
e8_status = 1;
}
}
/* Postprocess the data unless it cannot possibly contain 0xe8 bytes. */
if (e8_status)
lzx_postprocess(uncompressed_data, uncompressed_size);
return 0;
invalid:
return -1;
}
/*
* lzx_free_decompressor - Free an LZX decompressor
*
* @decompressor: A decompressor that was allocated with
* lzx_allocate_decompressor(), or NULL.
*/
void lzx_free_decompressor(struct lzx_decompressor *decompressor)
{
kfree(decompressor);
}
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