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_SPARC 137 # define XZ_DEC_SPARC 138 #endif 139 140 /* 141 * This will get the basic headers so that memeq() and others 142 * can be defined. 143 */ 144 #include "xz/xz_private.h" 145 146 /* 147 * Replace the normal allocation functions with the versions from 148 * <linux/decompress/mm.h>. vfree() needs to support vfree(NULL) 149 * when XZ_DYNALLOC is used, but the pre-boot free() doesn't support it. 150 * Workaround it here because the other decompressors don't need it. 151 */ 152 #undef kmalloc 153 #undef kfree 154 #undef vmalloc 155 #undef vfree 156 #define kmalloc(size, flags) malloc(size) 157 #define kfree(ptr) free(ptr) 158 #define vmalloc(size) malloc(size) 159 #define vfree(ptr) do { if (ptr != NULL) free(ptr); } while (0) 160 161 /* 162 * FIXME: Not all basic memory functions are provided in architecture-specific 163 * files (yet). We define our own versions here for now, but this should be 164 * only a temporary solution. 165 * 166 * memeq and memzero are not used much and any remotely sane implementation 167 * is fast enough. memcpy/memmove speed matters in multi-call mode, but 168 * the kernel image is decompressed in single-call mode, in which only 169 * memmove speed can matter and only if there is a lot of incompressible data 170 * (LZMA2 stores incompressible chunks in uncompressed form). Thus, the 171 * functions below should just be kept small; it's probably not worth 172 * optimizing for speed. 173 */ 174 175 #ifndef memeq 176 static bool memeq(const void *a, const void *b, size_t size) 177 { 178 const uint8_t *x = a; 179 const uint8_t *y = b; 180 size_t i; 181 182 for (i = 0; i < size; ++i) 183 if (x[i] != y[i]) 184 return false; 185 186 return true; 187 } 188 #endif 189 190 #ifndef memzero 191 static void memzero(void *buf, size_t size) 192 { 193 uint8_t *b = buf; 194 uint8_t *e = b + size; 195 196 while (b != e) 197 *b++ = '\0'; 198 } 199 #endif 200 201 #ifndef memmove 202 /* Not static to avoid a conflict with the prototype in the Linux headers. */ 203 void *memmove(void *dest, const void *src, size_t size) 204 { 205 uint8_t *d = dest; 206 const uint8_t *s = src; 207 size_t i; 208 209 if (d < s) { 210 for (i = 0; i < size; ++i) 211 d[i] = s[i]; 212 } else if (d > s) { 213 i = size; 214 while (i-- > 0) 215 d[i] = s[i]; 216 } 217 218 return dest; 219 } 220 #endif 221 222 /* 223 * Since we need memmove anyway, would use it as memcpy too. 224 * Commented out for now to avoid breaking things. 225 */ 226 /* 227 #ifndef memcpy 228 # define memcpy memmove 229 #endif 230 */ 231 232 #include "xz/xz_crc32.c" 233 #include "xz/xz_dec_stream.c" 234 #include "xz/xz_dec_lzma2.c" 235 #include "xz/xz_dec_bcj.c" 236 237 #endif /* XZ_PREBOOT */ 238 239 /* Size of the input and output buffers in multi-call mode */ 240 #define XZ_IOBUF_SIZE 4096 241 242 /* 243 * This function implements the API defined in <linux/decompress/generic.h>. 244 * 245 * This wrapper will automatically choose single-call or multi-call mode 246 * of the native XZ decoder API. The single-call mode can be used only when 247 * both input and output buffers are available as a single chunk, i.e. when 248 * fill() and flush() won't be used. 249 */ 250 STATIC int INIT unxz(unsigned char *in, long in_size, 251 long (*fill)(void *dest, unsigned long size), 252 long (*flush)(void *src, unsigned long size), 253 unsigned char *out, long *in_used, 254 void (*error)(char *x)) 255 { 256 struct xz_buf b; 257 struct xz_dec *s; 258 enum xz_ret ret; 259 bool must_free_in = false; 260 261 #if XZ_INTERNAL_CRC32 262 xz_crc32_init(); 263 #endif 264 265 if (in_used != NULL) 266 *in_used = 0; 267 268 if (fill == NULL && flush == NULL) 269 s = xz_dec_init(XZ_SINGLE, 0); 270 else 271 s = xz_dec_init(XZ_DYNALLOC, (uint32_t)-1); 272 273 if (s == NULL) 274 goto error_alloc_state; 275 276 if (flush == NULL) { 277 b.out = out; 278 b.out_size = (size_t)-1; 279 } else { 280 b.out_size = XZ_IOBUF_SIZE; 281 b.out = malloc(XZ_IOBUF_SIZE); 282 if (b.out == NULL) 283 goto error_alloc_out; 284 } 285 286 if (in == NULL) { 287 must_free_in = true; 288 in = malloc(XZ_IOBUF_SIZE); 289 if (in == NULL) 290 goto error_alloc_in; 291 } 292 293 b.in = in; 294 b.in_pos = 0; 295 b.in_size = in_size; 296 b.out_pos = 0; 297 298 if (fill == NULL && flush == NULL) { 299 ret = xz_dec_run(s, &b); 300 } else { 301 do { 302 if (b.in_pos == b.in_size && fill != NULL) { 303 if (in_used != NULL) 304 *in_used += b.in_pos; 305 306 b.in_pos = 0; 307 308 in_size = fill(in, XZ_IOBUF_SIZE); 309 if (in_size < 0) { 310 /* 311 * This isn't an optimal error code 312 * but it probably isn't worth making 313 * a new one either. 314 */ 315 ret = XZ_BUF_ERROR; 316 break; 317 } 318 319 b.in_size = in_size; 320 } 321 322 ret = xz_dec_run(s, &b); 323 324 if (flush != NULL && (b.out_pos == b.out_size 325 || (ret != XZ_OK && b.out_pos > 0))) { 326 /* 327 * Setting ret here may hide an error 328 * returned by xz_dec_run(), but probably 329 * it's not too bad. 330 */ 331 if (flush(b.out, b.out_pos) != (long)b.out_pos) 332 ret = XZ_BUF_ERROR; 333 334 b.out_pos = 0; 335 } 336 } while (ret == XZ_OK); 337 338 if (must_free_in) 339 free(in); 340 341 if (flush != NULL) 342 free(b.out); 343 } 344 345 if (in_used != NULL) 346 *in_used += b.in_pos; 347 348 xz_dec_end(s); 349 350 switch (ret) { 351 case XZ_STREAM_END: 352 return 0; 353 354 case XZ_MEM_ERROR: 355 /* This can occur only in multi-call mode. */ 356 error("XZ decompressor ran out of memory"); 357 break; 358 359 case XZ_FORMAT_ERROR: 360 error("Input is not in the XZ format (wrong magic bytes)"); 361 break; 362 363 case XZ_OPTIONS_ERROR: 364 error("Input was encoded with settings that are not " 365 "supported by this XZ decoder"); 366 break; 367 368 case XZ_DATA_ERROR: 369 case XZ_BUF_ERROR: 370 error("XZ-compressed data is corrupt"); 371 break; 372 373 default: 374 error("Bug in the XZ decompressor"); 375 break; 376 } 377 378 return -1; 379 380 error_alloc_in: 381 if (flush != NULL) 382 free(b.out); 383 384 error_alloc_out: 385 xz_dec_end(s); 386 387 error_alloc_state: 388 error("XZ decompressor ran out of memory"); 389 return -1; 390 } 391 392 /* 393 * This macro is used by architecture-specific files to decompress 394 * the kernel image. 395 */ 396 #ifdef XZ_PREBOOT 397 STATIC int INIT __decompress(unsigned char *buf, long len, 398 long (*fill)(void*, unsigned long), 399 long (*flush)(void*, unsigned long), 400 unsigned char *out_buf, long olen, 401 long *pos, 402 void (*error)(char *x)) 403 { 404 return unxz(buf, len, fill, flush, out_buf, pos, error); 405 } 406 #endif 407