1 /* 2 * Wrapper for decompressing XZ-compressed kernel, initramfs, and initrd 3 * 4 * Author: Lasse Collin <lasse.collin@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 * incompressible. Thus, we must look for worst-case expansion when the 24 * compressor is encoding incompressible data. 25 * 26 * The structure of the .xz file in case of a compressed 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 incompressible 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 #else 106 #include <linux/decompress/unxz.h> 107 #endif 108 #ifdef __KERNEL__ 109 # include <linux/decompress/mm.h> 110 #endif 111 #define XZ_EXTERN STATIC 112 113 #ifndef XZ_PREBOOT 114 # include <linux/slab.h> 115 # include <linux/xz.h> 116 #else 117 /* 118 * Use the internal CRC32 code instead of kernel's CRC32 module, which 119 * is not available in early phase of booting. 120 */ 121 #define XZ_INTERNAL_CRC32 1 122 123 /* 124 * For boot time use, we enable only the BCJ filter of the current 125 * architecture or none if no BCJ filter is available for the architecture. 126 */ 127 #ifdef CONFIG_X86 128 # define XZ_DEC_X86 129 #endif 130 #ifdef CONFIG_PPC 131 # define XZ_DEC_POWERPC 132 #endif 133 #ifdef CONFIG_ARM 134 # define XZ_DEC_ARM 135 #endif 136 #ifdef CONFIG_IA64 137 # define XZ_DEC_IA64 138 #endif 139 #ifdef CONFIG_SPARC 140 # define XZ_DEC_SPARC 141 #endif 142 143 /* 144 * This will get the basic headers so that memeq() and others 145 * can be defined. 146 */ 147 #include "xz/xz_private.h" 148 149 /* 150 * Replace the normal allocation functions with the versions from 151 * <linux/decompress/mm.h>. vfree() needs to support vfree(NULL) 152 * when XZ_DYNALLOC is used, but the pre-boot free() doesn't support it. 153 * Workaround it here because the other decompressors don't need it. 154 */ 155 #undef kmalloc 156 #undef kfree 157 #undef vmalloc 158 #undef vfree 159 #define kmalloc(size, flags) malloc(size) 160 #define kfree(ptr) free(ptr) 161 #define vmalloc(size) malloc(size) 162 #define vfree(ptr) do { if (ptr != NULL) free(ptr); } while (0) 163 164 /* 165 * FIXME: Not all basic memory functions are provided in architecture-specific 166 * files (yet). We define our own versions here for now, but this should be 167 * only a temporary solution. 168 * 169 * memeq and memzero are not used much and any remotely sane implementation 170 * is fast enough. memcpy/memmove speed matters in multi-call mode, but 171 * the kernel image is decompressed in single-call mode, in which only 172 * memmove speed can matter and only if there is a lot of incompressible data 173 * (LZMA2 stores incompressible chunks in uncompressed form). Thus, the 174 * functions below should just be kept small; it's probably not worth 175 * optimizing for speed. 176 */ 177 178 #ifndef memeq 179 static bool memeq(const void *a, const void *b, size_t size) 180 { 181 const uint8_t *x = a; 182 const uint8_t *y = b; 183 size_t i; 184 185 for (i = 0; i < size; ++i) 186 if (x[i] != y[i]) 187 return false; 188 189 return true; 190 } 191 #endif 192 193 #ifndef memzero 194 static void memzero(void *buf, size_t size) 195 { 196 uint8_t *b = buf; 197 uint8_t *e = b + size; 198 199 while (b != e) 200 *b++ = '\0'; 201 } 202 #endif 203 204 #ifndef memmove 205 /* Not static to avoid a conflict with the prototype in the Linux headers. */ 206 void *memmove(void *dest, const void *src, size_t size) 207 { 208 uint8_t *d = dest; 209 const uint8_t *s = src; 210 size_t i; 211 212 if (d < s) { 213 for (i = 0; i < size; ++i) 214 d[i] = s[i]; 215 } else if (d > s) { 216 i = size; 217 while (i-- > 0) 218 d[i] = s[i]; 219 } 220 221 return dest; 222 } 223 #endif 224 225 /* 226 * Since we need memmove anyway, would use it as memcpy too. 227 * Commented out for now to avoid breaking things. 228 */ 229 /* 230 #ifndef memcpy 231 # define memcpy memmove 232 #endif 233 */ 234 235 #include "xz/xz_crc32.c" 236 #include "xz/xz_dec_stream.c" 237 #include "xz/xz_dec_lzma2.c" 238 #include "xz/xz_dec_bcj.c" 239 240 #endif /* XZ_PREBOOT */ 241 242 /* Size of the input and output buffers in multi-call mode */ 243 #define XZ_IOBUF_SIZE 4096 244 245 /* 246 * This function implements the API defined in <linux/decompress/generic.h>. 247 * 248 * This wrapper will automatically choose single-call or multi-call mode 249 * of the native XZ decoder API. The single-call mode can be used only when 250 * both input and output buffers are available as a single chunk, i.e. when 251 * fill() and flush() won't be used. 252 */ 253 STATIC int INIT unxz(unsigned char *in, long in_size, 254 long (*fill)(void *dest, unsigned long size), 255 long (*flush)(void *src, unsigned long size), 256 unsigned char *out, long *in_used, 257 void (*error)(char *x)) 258 { 259 struct xz_buf b; 260 struct xz_dec *s; 261 enum xz_ret ret; 262 bool must_free_in = false; 263 264 #if XZ_INTERNAL_CRC32 265 xz_crc32_init(); 266 #endif 267 268 if (in_used != NULL) 269 *in_used = 0; 270 271 if (fill == NULL && flush == NULL) 272 s = xz_dec_init(XZ_SINGLE, 0); 273 else 274 s = xz_dec_init(XZ_DYNALLOC, (uint32_t)-1); 275 276 if (s == NULL) 277 goto error_alloc_state; 278 279 if (flush == NULL) { 280 b.out = out; 281 b.out_size = (size_t)-1; 282 } else { 283 b.out_size = XZ_IOBUF_SIZE; 284 b.out = malloc(XZ_IOBUF_SIZE); 285 if (b.out == NULL) 286 goto error_alloc_out; 287 } 288 289 if (in == NULL) { 290 must_free_in = true; 291 in = malloc(XZ_IOBUF_SIZE); 292 if (in == NULL) 293 goto error_alloc_in; 294 } 295 296 b.in = in; 297 b.in_pos = 0; 298 b.in_size = in_size; 299 b.out_pos = 0; 300 301 if (fill == NULL && flush == NULL) { 302 ret = xz_dec_run(s, &b); 303 } else { 304 do { 305 if (b.in_pos == b.in_size && fill != NULL) { 306 if (in_used != NULL) 307 *in_used += b.in_pos; 308 309 b.in_pos = 0; 310 311 in_size = fill(in, XZ_IOBUF_SIZE); 312 if (in_size < 0) { 313 /* 314 * This isn't an optimal error code 315 * but it probably isn't worth making 316 * a new one either. 317 */ 318 ret = XZ_BUF_ERROR; 319 break; 320 } 321 322 b.in_size = in_size; 323 } 324 325 ret = xz_dec_run(s, &b); 326 327 if (flush != NULL && (b.out_pos == b.out_size 328 || (ret != XZ_OK && b.out_pos > 0))) { 329 /* 330 * Setting ret here may hide an error 331 * returned by xz_dec_run(), but probably 332 * it's not too bad. 333 */ 334 if (flush(b.out, b.out_pos) != (long)b.out_pos) 335 ret = XZ_BUF_ERROR; 336 337 b.out_pos = 0; 338 } 339 } while (ret == XZ_OK); 340 341 if (must_free_in) 342 free(in); 343 344 if (flush != NULL) 345 free(b.out); 346 } 347 348 if (in_used != NULL) 349 *in_used += b.in_pos; 350 351 xz_dec_end(s); 352 353 switch (ret) { 354 case XZ_STREAM_END: 355 return 0; 356 357 case XZ_MEM_ERROR: 358 /* This can occur only in multi-call mode. */ 359 error("XZ decompressor ran out of memory"); 360 break; 361 362 case XZ_FORMAT_ERROR: 363 error("Input is not in the XZ format (wrong magic bytes)"); 364 break; 365 366 case XZ_OPTIONS_ERROR: 367 error("Input was encoded with settings that are not " 368 "supported by this XZ decoder"); 369 break; 370 371 case XZ_DATA_ERROR: 372 case XZ_BUF_ERROR: 373 error("XZ-compressed data is corrupt"); 374 break; 375 376 default: 377 error("Bug in the XZ decompressor"); 378 break; 379 } 380 381 return -1; 382 383 error_alloc_in: 384 if (flush != NULL) 385 free(b.out); 386 387 error_alloc_out: 388 xz_dec_end(s); 389 390 error_alloc_state: 391 error("XZ decompressor ran out of memory"); 392 return -1; 393 } 394 395 /* 396 * This macro is used by architecture-specific files to decompress 397 * the kernel image. 398 */ 399 #ifdef XZ_PREBOOT 400 STATIC int INIT __decompress(unsigned char *buf, long len, 401 long (*fill)(void*, unsigned long), 402 long (*flush)(void*, unsigned long), 403 unsigned char *out_buf, long olen, 404 long *pos, 405 void (*error)(char *x)) 406 { 407 return unxz(buf, len, fill, flush, out_buf, pos, error); 408 } 409 #endif 410