summaryrefslogtreecommitdiffstats
path: root/minelf/Retouch.c
blob: a25380b3422c33eb024092644dfd73416c7551fd (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
/*
 * Copyright (C) 2009 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include <errno.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <strings.h>
#include "Retouch.h"
#include "applypatch/applypatch.h"

typedef struct {
    int32_t mmap_addr;
    char tag[4]; /* 'P', 'R', 'E', ' ' */
} prelink_info_t __attribute__((packed));

#define false 0
#define true 1

static int32_t offs_prev;
static uint32_t cont_prev;

static void init_compression_state(void) {
    offs_prev = 0;
    cont_prev = 0;
}

// For details on the encoding used for relocation lists, please
// refer to build/tools/retouch/retouch-prepare.c. The intent is to
// save space by removing most of the inherent redundancy.

static void decode_bytes(uint8_t *encoded_bytes, int encoded_size,
                         int32_t *dst_offset, uint32_t *dst_contents) {
    if (encoded_size == 2) {
        *dst_offset = offs_prev + (((encoded_bytes[0]&0x60)>>5)+1)*4;

        // if the original was negative, we need to 1-pad before applying delta
        int32_t tmp = (((encoded_bytes[0] & 0x0000001f) << 8) |
                       encoded_bytes[1]);
        if (tmp & 0x1000) tmp = 0xffffe000 | tmp;
        *dst_contents = cont_prev + tmp;
    } else if (encoded_size == 3) {
        *dst_offset = offs_prev + (((encoded_bytes[0]&0x30)>>4)+1)*4;

        // if the original was negative, we need to 1-pad before applying delta
        int32_t tmp = (((encoded_bytes[0] & 0x0000000f) << 16) |
                       (encoded_bytes[1] << 8) |
                       encoded_bytes[2]);
        if (tmp & 0x80000) tmp = 0xfff00000 | tmp;
        *dst_contents = cont_prev + tmp;
    } else {
        *dst_offset =
          (encoded_bytes[0]<<24) |
          (encoded_bytes[1]<<16) |
          (encoded_bytes[2]<<8) |
          encoded_bytes[3];
        if (*dst_offset == 0x3fffffff) *dst_offset = -1;
        *dst_contents =
          (encoded_bytes[4]<<24) |
          (encoded_bytes[5]<<16) |
          (encoded_bytes[6]<<8) |
          encoded_bytes[7];
    }
}

static uint8_t *decode_in_memory(uint8_t *encoded_bytes,
                                 int32_t *offset, uint32_t *contents) {
    int input_size, charIx;
    uint8_t input[8];

    input[0] = *(encoded_bytes++);
    if (input[0] & 0x80)
        input_size = 2;
    else if (input[0] & 0x40)
        input_size = 3;
    else
        input_size = 8;

    // we already read one byte..
    charIx = 1;
    while (charIx < input_size) {
        input[charIx++] = *(encoded_bytes++);
    }

    // depends on the decoder state!
    decode_bytes(input, input_size, offset, contents);

    offs_prev = *offset;
    cont_prev = *contents;

    return encoded_bytes;
}

int retouch_mask_data(uint8_t *binary_object,
                      int32_t binary_size,
                      int32_t *desired_offset,
                      int32_t *retouch_offset) {
    retouch_info_t *r_info;
    prelink_info_t *p_info;

    int32_t target_offset = 0;
    if (desired_offset) target_offset = *desired_offset;

    int32_t p_offs = binary_size-sizeof(prelink_info_t); // prelink_info_t
    int32_t r_offs = p_offs-sizeof(retouch_info_t); // retouch_info_t
    int32_t b_offs; // retouch data blob

    // If not retouched, we say it was a match. This might get invoked on
    // non-retouched binaries, so that's why we need to do this.
    if (retouch_offset != NULL) *retouch_offset = target_offset;
    if (r_offs < 0) return (desired_offset == NULL) ?
                      RETOUCH_DATA_NOTAPPLICABLE : RETOUCH_DATA_MATCHED;
    p_info = (prelink_info_t *)(binary_object+p_offs);
    r_info = (retouch_info_t *)(binary_object+r_offs);
    if (strncmp(p_info->tag, "PRE ", 4) ||
        strncmp(r_info->tag, "RETOUCH ", 8))
        return (desired_offset == NULL) ?
          RETOUCH_DATA_NOTAPPLICABLE : RETOUCH_DATA_MATCHED;

    b_offs = r_offs-r_info->blob_size;
    if (b_offs < 0) {
        printf("negative binary offset: %d = %d - %d\n",
               b_offs, r_offs, r_info->blob_size);
        return RETOUCH_DATA_ERROR;
    }
    uint8_t *b_ptr = binary_object+b_offs;

    // Retouched: let's go through the work then.
    int32_t offset_candidate = target_offset;
    bool offset_set = false, offset_mismatch = false;
    init_compression_state();
    while (b_ptr < (uint8_t *)r_info) {
        int32_t retouch_entry_offset;
        uint32_t *retouch_entry;
        uint32_t retouch_original_value;

        b_ptr = decode_in_memory(b_ptr,
                                 &retouch_entry_offset,
                                 &retouch_original_value);
        if (retouch_entry_offset < (-1) ||
            retouch_entry_offset >= b_offs) {
            printf("bad retouch_entry_offset: %d", retouch_entry_offset);
            return RETOUCH_DATA_ERROR;
        }

        // "-1" means this is the value in prelink_info_t, which also gets
        // randomized.
        if (retouch_entry_offset == -1)
            retouch_entry = (uint32_t *)&(p_info->mmap_addr);
        else
            retouch_entry = (uint32_t *)(binary_object+retouch_entry_offset);

        if (desired_offset)
            *retouch_entry = retouch_original_value + target_offset;

        // Infer the randomization shift, compare to previously inferred.
        int32_t offset_of_this_entry = (int32_t)(*retouch_entry-
                                                 retouch_original_value);
        if (!offset_set) {
            offset_candidate = offset_of_this_entry;
            offset_set = true;
        } else {
            if (offset_candidate != offset_of_this_entry) {
                offset_mismatch = true;
                printf("offset is mismatched: %d, this entry is %d,"
                       " original 0x%x @ 0x%x",
                       offset_candidate, offset_of_this_entry,
                       retouch_original_value, retouch_entry_offset);
            }
        }
    }
    if (b_ptr > (uint8_t *)r_info) {
        printf("b_ptr went too far: %p, while r_info is %p",
               b_ptr, r_info);
        return RETOUCH_DATA_ERROR;
    }

    if (offset_mismatch) return RETOUCH_DATA_MISMATCHED;
    if (retouch_offset != NULL) *retouch_offset = offset_candidate;
    return RETOUCH_DATA_MATCHED;
}

// On success, _override is set to the offset that was actually applied.
// This implies that once we randomize to an offset we stick with it.
// This in turn is necessary in order to guarantee recovery after crash.
bool retouch_one_library(const char *binary_name,
                         const char *binary_sha1,
                         int32_t retouch_offset,
                         int32_t *retouch_offset_override) {
    bool success = true;
    int result;

    FileContents file;
    file.data = NULL;

    char binary_name_atomic[strlen(binary_name)+10];
    strcpy(binary_name_atomic, binary_name);
    strcat(binary_name_atomic, ".atomic");

    // We need a path that exists for calling statfs() later.
    //
    // Assume that binary_name (eg "/system/app/Foo.apk") is located
    // on the same filesystem as its top-level directory ("/system").
    char target_fs[strlen(binary_name)+1];
    char* slash = strchr(binary_name+1, '/');
    if (slash != NULL) {
        int count = slash - binary_name;
        strncpy(target_fs, binary_name, count);
        target_fs[count] = '\0';
    } else {
        strcpy(target_fs, binary_name);
    }

    result = LoadFileContents(binary_name, &file, RETOUCH_DONT_MASK);

    if (result == 0) {
        // Figure out the *apparent* offset to which this file has been
        // retouched. If it looks good, we will skip processing (we might
        // have crashed and during this recovery pass we don't want to
        // overwrite a valuable saved file in /cache---which would happen
        // if we blindly retouch everything again). NOTE: This implies
        // that we might have to override the supplied retouch offset. We
        // can do the override only once though: everything should match
        // afterward.

        int32_t inferred_offset;
        int retouch_probe_result = retouch_mask_data(file.data,
                                                     file.size,
                                                     NULL,
                                                     &inferred_offset);

        if (retouch_probe_result == RETOUCH_DATA_MATCHED) {
            if ((retouch_offset == inferred_offset) ||
                ((retouch_offset != 0 && inferred_offset != 0) &&
                 (retouch_offset_override != NULL))) {
                // This file is OK already and we are allowed to override.
                // Let's just return the offset override value. It is critical
                // to skip regardless of override: a broken file might need
                // recovery down the list and we should not mess up the saved
                // copy by doing unnecessary retouching.
                //
                // NOTE: If retouching was already started with a different
                // value, we will not be allowed to override. This happens
                // if on the retouch list there is a patched binary (which is
                // masked in apply_patch()) before there is a non-patched
                // binary.
                if (retouch_offset_override != NULL)
                    *retouch_offset_override = inferred_offset;
                success = true;
                goto out;
            } else {
                // Retouch to zero (mask the retouching), to make sure that
                // the SHA-1 check will pass below.
                int32_t zero = 0;
                retouch_mask_data(file.data, file.size, &zero, NULL);
                SHA(file.data, file.size, file.sha1);
            }
        }

        if (retouch_probe_result == RETOUCH_DATA_NOTAPPLICABLE) {
            // In the case of not retouchable, fake it. We do not want
            // to do the normal processing and overwrite the backup file:
            // we might be recovering!
            //
            // We return a zero override, which tells the caller that we
            // simply skipped the file.
            if (retouch_offset_override != NULL)
                *retouch_offset_override = 0;
            success = true;
            goto out;
        }

        // If we get here, either there was a mismatch in the offset, or
        // the file has not been processed yet. Continue with normal
        // processing.
    }

    if (result != 0 || FindMatchingPatch(file.sha1, &binary_sha1, 1) < 0) {
        free(file.data);
        printf("Attempting to recover source from '%s' ...\n",
               CACHE_TEMP_SOURCE);
        result = LoadFileContents(CACHE_TEMP_SOURCE, &file, RETOUCH_DO_MASK);
        if (result != 0 || FindMatchingPatch(file.sha1, &binary_sha1, 1) < 0) {
            printf(" failed.\n");
            success = false;
            goto out;
        }
        printf(" succeeded.\n");
    }

    // Retouch in-memory before worrying about backing up the original.
    //
    // Recovery steps will be oblivious to the actual retouch offset used,
    // so might as well write out the already-retouched copy. Then, in the
    // usual case, we will just swap the file locally, with no more writes
    // needed. In the no-free-space case, we will then write the same to the
    // original location.

    result = retouch_mask_data(file.data, file.size, &retouch_offset, NULL);
    if (result != RETOUCH_DATA_MATCHED) {
        success = false;
        goto out;
    }
    if (retouch_offset_override != NULL)
        *retouch_offset_override = retouch_offset;

    // How much free space do we need?
    bool enough_space = false;
    size_t free_space = FreeSpaceForFile(target_fs);
    // 50% margin when estimating the space needed.
    enough_space = (free_space > (file.size * 3 / 2));

    // The experts say we have to allow for a retry of the
    // whole process to avoid filesystem weirdness.
    int retry = 1;
    bool made_copy = false;
    do {
        // First figure out where to store a copy of the original.
        // Ideally leave the original itself intact until the
        // atomic swap. If no room on the same partition, fall back
        // to the cache partition and remove the original.

        if (!enough_space) {
            printf("Target is %ldB; free space is %ldB: not enough.\n",
                   (long)file.size, (long)free_space);

            retry = 0;
            if (MakeFreeSpaceOnCache(file.size) < 0) {
                printf("Not enough free space on '/cache'.\n");
                success = false;
                goto out;
            }
            if (SaveFileContents(CACHE_TEMP_SOURCE, &file) < 0) {
                printf("Failed to back up source file.\n");
                success = false;
                goto out;
            }
            made_copy = true;
            unlink(binary_name);

            size_t free_space = FreeSpaceForFile(target_fs);
            printf("(now %ld bytes free for target)\n", (long)free_space);
        }

        result = SaveFileContents(binary_name_atomic, &file);
        if (result != 0) {
            // Maybe the filesystem was optimistic: retry.
            enough_space = false;
            unlink(binary_name_atomic);
            printf("Saving the retouched contents failed; retrying.\n");
            continue;
        }

        // Succeeded; no need to retry.
        break;
    } while (retry-- > 0);

    // Give the .atomic file the same owner, group, and mode of the
    // original source file.
    if (chmod(binary_name_atomic, file.st.st_mode) != 0) {
        printf("chmod of \"%s\" failed: %s\n",
               binary_name_atomic, strerror(errno));
        success = false;
        goto out;
    }
    if (chown(binary_name_atomic, file.st.st_uid, file.st.st_gid) != 0) {
        printf("chown of \"%s\" failed: %s\n",
               binary_name_atomic,
               strerror(errno));
        success = false;
        goto out;
    }

    // Finally, rename the .atomic file to replace the target file.
    if (rename(binary_name_atomic, binary_name) != 0) {
        printf("rename of .atomic to \"%s\" failed: %s\n",
               binary_name, strerror(errno));
        success = false;
        goto out;
    }

    // If this run created a copy, and we're here, we can delete it.
    if (made_copy) unlink(CACHE_TEMP_SOURCE);

  out:
    // clean up
    free(file.data);
    unlink(binary_name_atomic);

    return success;
}