1 /* 2 * Wrapper for decompressing XZ-compressed kernel, initramfs, and initrd 3 * 4 * Author: Lasse Collin <lasse.collin (at) tukaani.org> 5 * 6 * This file has been put into the public domain. 7 * You can do whatever you want with this file. 8 */ 9 10 /* 11 * Important notes about in-place decompression 12 * 13 * At least on x86, the kernel is decompressed in place: the compressed data 14 * is placed to the end of the output buffer, and the decompressor overwrites 15 * most of the compressed data. There must be enough safety margin to 16 * guarantee that the write position is always behind the read position. 17 * 18 * The safety margin for XZ with LZMA2 or BCJ+LZMA2 is calculated below. 19 * Note that the margin with XZ is bigger than with Deflate (gzip)! 20 * 21 * The worst case for in-place decompression is that the beginning of 22 * the file is compressed extremely well, and the rest of the file is 23 * uncompressible. Thus, we must look for worst-case expansion when the 24 * compressor is encoding uncompressible data. 25 * 26 * The structure of the .xz file in case of a compresed kernel is as follows. 27 * Sizes (as bytes) of the fields are in parenthesis. 28 * 29 * Stream Header (12) 30 * Block Header: 31 * Block Header (8-12) 32 * Compressed Data (N) 33 * Block Padding (0-3) 34 * CRC32 (4) 35 * Index (8-20) 36 * Stream Footer (12) 37 * 38 * Normally there is exactly one Block, but let's assume that there are 39 * 2-4 Blocks just in case. Because Stream Header and also Block Header 40 * of the first Block don't make the decompressor produce any uncompressed 41 * data, we can ignore them from our calculations. Block Headers of possible 42 * additional Blocks have to be taken into account still. With these 43 * assumptions, it is safe to assume that the total header overhead is 44 * less than 128 bytes. 45 * 46 * Compressed Data contains LZMA2 or BCJ+LZMA2 encoded data. Since BCJ 47 * doesn't change the size of the data, it is enough to calculate the 48 * safety margin for LZMA2. 49 * 50 * LZMA2 stores the data in chunks. Each chunk has a header whose size is 51 * a maximum of 6 bytes, but to get round 2^n numbers, let's assume that 52 * the maximum chunk header size is 8 bytes. After the chunk header, there 53 * may be up to 64 KiB of actual payload in the chunk. Often the payload is 54 * quite a bit smaller though; to be safe, let's assume that an average 55 * chunk has only 32 KiB of payload. 56 * 57 * The maximum uncompressed size of the payload is 2 MiB. The minimum 58 * uncompressed size of the payload is in practice never less than the 59 * payload size itself. The LZMA2 format would allow uncompressed size 60 * to be less than the payload size, but no sane compressor creates such 61 * files. LZMA2 supports storing uncompressible data in uncompressed form, 62 * so there's never a need to create payloads whose uncompressed size is 63 * smaller than the compressed size. 64 * 65 * The assumption, that the uncompressed size of the payload is never 66 * smaller than the payload itself, is valid only when talking about 67 * the payload as a whole. It is possible that the payload has parts where 68 * the decompressor consumes more input than it produces output. Calculating 69 * the worst case for this would be tricky. Instead of trying to do that, 70 * let's simply make sure that the decompressor never overwrites any bytes 71 * of the payload which it is currently reading. 72 * 73 * Now we have enough information to calculate the safety margin. We need 74 * - 128 bytes for the .xz file format headers; 75 * - 8 bytes per every 32 KiB of uncompressed size (one LZMA2 chunk header 76 * per chunk, each chunk having average payload size of 32 KiB); and 77 * - 64 KiB (biggest possible LZMA2 chunk payload size) to make sure that 78 * the decompressor never overwrites anything from the LZMA2 chunk 79 * payload it is currently reading. 80 * 81 * We get the following formula: 82 * 83 * safety_margin = 128 + uncompressed_size * 8 / 32768 + 65536 84 * = 128 + (uncompressed_size >> 12) + 65536 85 * 86 * For comparison, according to arch/x86/boot/compressed/misc.c, the 87 * equivalent formula for Deflate is this: 88 * 89 * safety_margin = 18 + (uncompressed_size >> 12) + 32768 90 * 91 * Thus, when updating Deflate-only in-place kernel decompressor to 92 * support XZ, the fixed overhead has to be increased from 18+32768 bytes 93 * to 128+65536 bytes. 94 */ 95 96 /* 97 * STATIC is defined to "static" if we are being built for kernel 98 * decompression (pre-boot code). <linux/decompress/mm.h> will define 99 * STATIC to empty if it wasn't already defined. Since we will need to 100 * know later if we are being used for kernel decompression, we define 101 * XZ_PREBOOT here. 102 */ 103 #ifdef STATIC 104 # define XZ_PREBOOT 105 #endif 106 #ifdef __KERNEL__ 107 # include <linux/decompress/mm.h> 108 #endif 109 #define XZ_EXTERN STATIC 110 111 #ifndef XZ_PREBOOT 112 # include <linux/slab.h> 113 # include <linux/xz.h> 114 #else 115 /* 116 * Use the internal CRC32 code instead of kernel's CRC32 module, which 117 * is not available in early phase of booting. 118 */ 119 #define XZ_INTERNAL_CRC32 1 120 121 /* 122 * For boot time use, we enable only the BCJ filter of the current 123 * architecture or none if no BCJ filter is available for the architecture. 124 */ 125 #ifdef CONFIG_X86 126 # define XZ_DEC_X86 127 #endif 128 #ifdef CONFIG_PPC 129 # define XZ_DEC_POWERPC 130 #endif 131 #ifdef CONFIG_ARM 132 # define XZ_DEC_ARM 133 #endif 134 #ifdef CONFIG_IA64 135 # define XZ_DEC_IA64 136 #endif 137 #ifdef CONFIG_SPARC 138 # define XZ_DEC_SPARC 139 #endif 140 141 /* 142 * This will get the basic headers so that memeq() and others 143 * can be defined. 144 */ 145 #include "xz/xz_private.h" 146 147 /* 148 * Replace the normal allocation functions with the versions from 149 * <linux/decompress/mm.h>. vfree() needs to support vfree(NULL) 150 * when XZ_DYNALLOC is used, but the pre-boot free() doesn't support it. 151 * Workaround it here because the other decompressors don't need it. 152 */ 153 #undef kmalloc 154 #undef kfree 155 #undef vmalloc 156 #undef vfree 157 #define kmalloc(size, flags) malloc(size) 158 #define kfree(ptr) free(ptr) 159 #define vmalloc(size) malloc(size) 160 #define vfree(ptr) do { if (ptr != NULL) free(ptr); } while (0) 161 162 /* 163 * FIXME: Not all basic memory functions are provided in architecture-specific 164 * files (yet). We define our own versions here for now, but this should be 165 * only a temporary solution. 166 * 167 * memeq and memzero are not used much and any remotely sane implementation 168 * is fast enough. memcpy/memmove speed matters in multi-call mode, but 169 * the kernel image is decompressed in single-call mode, in which only 170 * memcpy speed can matter and only if there is a lot of uncompressible data 171 * (LZMA2 stores uncompressible chunks in uncompressed form). Thus, the 172 * functions below should just be kept small; it's probably not worth 173 * optimizing for speed. 174 */ 175 176 #ifndef memeq 177 static bool memeq(const void *a, const void *b, size_t size) 178 { 179 const uint8_t *x = a; 180 const uint8_t *y = b; 181 size_t i; 182 183 for (i = 0; i < size; ++i) 184 if (x[i] != y[i]) 185 return false; 186 187 return true; 188 } 189 #endif 190 191 #ifndef memzero 192 static void memzero(void *buf, size_t size) 193 { 194 uint8_t *b = buf; 195 uint8_t *e = b + size; 196 197 while (b != e) 198 *b++ = '\0'; 199 } 200 #endif 201 202 #ifndef memmove 203 /* Not static to avoid a conflict with the prototype in the Linux headers. */ 204 void *memmove(void *dest, const void *src, size_t size) 205 { 206 uint8_t *d = dest; 207 const uint8_t *s = src; 208 size_t i; 209 210 if (d < s) { 211 for (i = 0; i < size; ++i) 212 d[i] = s[i]; 213 } else if (d > s) { 214 i = size; 215 while (i-- > 0) 216 d[i] = s[i]; 217 } 218 219 return dest; 220 } 221 #endif 222 223 /* 224 * Since we need memmove anyway, would use it as memcpy too. 225 * Commented out for now to avoid breaking things. 226 */ 227 /* 228 #ifndef memcpy 229 # define memcpy memmove 230 #endif 231 */ 232 233 #include "xz/xz_crc32.c" 234 #include "xz/xz_dec_stream.c" 235 #include "xz/xz_dec_lzma2.c" 236 #include "xz/xz_dec_bcj.c" 237 238 #endif /* XZ_PREBOOT */ 239 240 /* Size of the input and output buffers in multi-call mode */ 241 #define XZ_IOBUF_SIZE 4096 242 243 /* 244 * This function implements the API defined in <linux/decompress/generic.h>. 245 * 246 * This wrapper will automatically choose single-call or multi-call mode 247 * of the native XZ decoder API. The single-call mode can be used only when 248 * both input and output buffers are available as a single chunk, i.e. when 249 * fill() and flush() won't be used. 250 */ 251 STATIC int INIT unxz(unsigned char *in, int in_size, 252 int (*fill)(void *dest, unsigned int size), 253 int (*flush)(void *src, unsigned int size), 254 unsigned char *out, int *in_used, 255 void (*error)(char *x)) 256 { 257 struct xz_buf b; 258 struct xz_dec *s; 259 enum xz_ret ret; 260 bool must_free_in = false; 261 262 #if XZ_INTERNAL_CRC32 263 xz_crc32_init(); 264 #endif 265 266 if (in_used != NULL) 267 *in_used = 0; 268 269 if (fill == NULL && flush == NULL) 270 s = xz_dec_init(XZ_SINGLE, 0); 271 else 272 s = xz_dec_init(XZ_DYNALLOC, (uint32_t)-1); 273 274 if (s == NULL) 275 goto error_alloc_state; 276 277 if (flush == NULL) { 278 b.out = out; 279 b.out_size = (size_t)-1; 280 } else { 281 b.out_size = XZ_IOBUF_SIZE; 282 b.out = malloc(XZ_IOBUF_SIZE); 283 if (b.out == NULL) 284 goto error_alloc_out; 285 } 286 287 if (in == NULL) { 288 must_free_in = true; 289 in = malloc(XZ_IOBUF_SIZE); 290 if (in == NULL) 291 goto error_alloc_in; 292 } 293 294 b.in = in; 295 b.in_pos = 0; 296 b.in_size = in_size; 297 b.out_pos = 0; 298 299 if (fill == NULL && flush == NULL) { 300 ret = xz_dec_run(s, &b); 301 } else { 302 do { 303 if (b.in_pos == b.in_size && fill != NULL) { 304 if (in_used != NULL) 305 *in_used += b.in_pos; 306 307 b.in_pos = 0; 308 309 in_size = fill(in, XZ_IOBUF_SIZE); 310 if (in_size < 0) { 311 /* 312 * This isn't an optimal error code 313 * but it probably isn't worth making 314 * a new one either. 315 */ 316 ret = XZ_BUF_ERROR; 317 break; 318 } 319 320 b.in_size = in_size; 321 } 322 323 ret = xz_dec_run(s, &b); 324 325 if (flush != NULL && (b.out_pos == b.out_size 326 || (ret != XZ_OK && b.out_pos > 0))) { 327 /* 328 * Setting ret here may hide an error 329 * returned by xz_dec_run(), but probably 330 * it's not too bad. 331 */ 332 if (flush(b.out, b.out_pos) != (int)b.out_pos) 333 ret = XZ_BUF_ERROR; 334 335 b.out_pos = 0; 336 } 337 } while (ret == XZ_OK); 338 339 if (must_free_in) 340 free(in); 341 342 if (flush != NULL) 343 free(b.out); 344 } 345 346 if (in_used != NULL) 347 *in_used += b.in_pos; 348 349 xz_dec_end(s); 350 351 switch (ret) { 352 case XZ_STREAM_END: 353 return 0; 354 355 case XZ_MEM_ERROR: 356 /* This can occur only in multi-call mode. */ 357 error("XZ decompressor ran out of memory"); 358 break; 359 360 case XZ_FORMAT_ERROR: 361 error("Input is not in the XZ format (wrong magic bytes)"); 362 break; 363 364 case XZ_OPTIONS_ERROR: 365 error("Input was encoded with settings that are not " 366 "supported by this XZ decoder"); 367 break; 368 369 case XZ_DATA_ERROR: 370 case XZ_BUF_ERROR: 371 error("XZ-compressed data is corrupt"); 372 break; 373 374 default: 375 error("Bug in the XZ decompressor"); 376 break; 377 } 378 379 return -1; 380 381 error_alloc_in: 382 if (flush != NULL) 383 free(b.out); 384 385 error_alloc_out: 386 xz_dec_end(s); 387 388 error_alloc_state: 389 error("XZ decompressor ran out of memory"); 390 return -1; 391 } 392 393 /* 394 * This macro is used by architecture-specific files to decompress 395 * the kernel image. 396 */ 397 #define decompress unxz 398
