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Diffstat (limited to '')
| -rw-r--r-- | lib/decompress_unxz.c | 407 |
1 files changed, 407 insertions, 0 deletions
diff --git a/lib/decompress_unxz.c b/lib/decompress_unxz.c new file mode 100644 index 000000000..9f4262ee3 --- /dev/null +++ b/lib/decompress_unxz.c @@ -0,0 +1,407 @@ +/* + * 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 |