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
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