Root/lib/decompress_unxz.c

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 * 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
177static 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
192static 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. */
204void *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 */
251STATIC 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
381error_alloc_in:
382    if (flush != NULL)
383        free(b.out);
384
385error_alloc_out:
386    xz_dec_end(s);
387
388error_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

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