summaryrefslogtreecommitdiff
path: root/include/linux/fortify-string.h
blob: da51a83b28293c4229a4585c7abd5e0cf0f8ba51 (plain)
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
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _LINUX_FORTIFY_STRING_H_
#define _LINUX_FORTIFY_STRING_H_

#include <linux/bug.h>
#include <linux/const.h>
#include <linux/limits.h>

#define __FORTIFY_INLINE extern __always_inline __gnu_inline __overloadable
#define __RENAME(x) __asm__(#x)

void fortify_panic(const char *name) __noreturn __cold;
void __read_overflow(void) __compiletime_error("detected read beyond size of object (1st parameter)");
void __read_overflow2(void) __compiletime_error("detected read beyond size of object (2nd parameter)");
void __read_overflow2_field(size_t avail, size_t wanted) __compiletime_warning("detected read beyond size of field (2nd parameter); maybe use struct_group()?");
void __write_overflow(void) __compiletime_error("detected write beyond size of object (1st parameter)");
void __write_overflow_field(size_t avail, size_t wanted) __compiletime_warning("detected write beyond size of field (1st parameter); maybe use struct_group()?");

#define __compiletime_strlen(p)					\
({								\
	char *__p = (char *)(p);				\
	size_t __ret = SIZE_MAX;				\
	const size_t __p_size = __member_size(p);		\
	if (__p_size != SIZE_MAX &&				\
	    __builtin_constant_p(*__p)) {			\
		size_t __p_len = __p_size - 1;			\
		if (__builtin_constant_p(__p[__p_len]) &&	\
		    __p[__p_len] == '\0')			\
			__ret = __builtin_strlen(__p);		\
	}							\
	__ret;							\
})

#if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
extern void *__underlying_memchr(const void *p, int c, __kernel_size_t size) __RENAME(memchr);
extern int __underlying_memcmp(const void *p, const void *q, __kernel_size_t size) __RENAME(memcmp);
extern void *__underlying_memcpy(void *p, const void *q, __kernel_size_t size) __RENAME(memcpy);
extern void *__underlying_memmove(void *p, const void *q, __kernel_size_t size) __RENAME(memmove);
extern void *__underlying_memset(void *p, int c, __kernel_size_t size) __RENAME(memset);
extern char *__underlying_strcat(char *p, const char *q) __RENAME(strcat);
extern char *__underlying_strcpy(char *p, const char *q) __RENAME(strcpy);
extern __kernel_size_t __underlying_strlen(const char *p) __RENAME(strlen);
extern char *__underlying_strncat(char *p, const char *q, __kernel_size_t count) __RENAME(strncat);
extern char *__underlying_strncpy(char *p, const char *q, __kernel_size_t size) __RENAME(strncpy);
#else

#if defined(__SANITIZE_MEMORY__)
/*
 * For KMSAN builds all memcpy/memset/memmove calls should be replaced by the
 * corresponding __msan_XXX functions.
 */
#include <linux/kmsan_string.h>
#define __underlying_memcpy	__msan_memcpy
#define __underlying_memmove	__msan_memmove
#define __underlying_memset	__msan_memset
#else
#define __underlying_memcpy	__builtin_memcpy
#define __underlying_memmove	__builtin_memmove
#define __underlying_memset	__builtin_memset
#endif

#define __underlying_memchr	__builtin_memchr
#define __underlying_memcmp	__builtin_memcmp
#define __underlying_strcat	__builtin_strcat
#define __underlying_strcpy	__builtin_strcpy
#define __underlying_strlen	__builtin_strlen
#define __underlying_strncat	__builtin_strncat
#define __underlying_strncpy	__builtin_strncpy
#endif

/**
 * unsafe_memcpy - memcpy implementation with no FORTIFY bounds checking
 *
 * @dst: Destination memory address to write to
 * @src: Source memory address to read from
 * @bytes: How many bytes to write to @dst from @src
 * @justification: Free-form text or comment describing why the use is needed
 *
 * This should be used for corner cases where the compiler cannot do the
 * right thing, or during transitions between APIs, etc. It should be used
 * very rarely, and includes a place for justification detailing where bounds
 * checking has happened, and why existing solutions cannot be employed.
 */
#define unsafe_memcpy(dst, src, bytes, justification)		\
	__underlying_memcpy(dst, src, bytes)

/*
 * Clang's use of __builtin_*object_size() within inlines needs hinting via
 * __pass_*object_size(). The preference is to only ever use type 1 (member
 * size, rather than struct size), but there remain some stragglers using
 * type 0 that will be converted in the future.
 */
#if __has_builtin(__builtin_dynamic_object_size)
#define POS			__pass_dynamic_object_size(1)
#define POS0			__pass_dynamic_object_size(0)
#define __struct_size(p)	__builtin_dynamic_object_size(p, 0)
#define __member_size(p)	__builtin_dynamic_object_size(p, 1)
#else
#define POS			__pass_object_size(1)
#define POS0			__pass_object_size(0)
#define __struct_size(p)	__builtin_object_size(p, 0)
#define __member_size(p)	__builtin_object_size(p, 1)
#endif

#define __compiletime_lessthan(bounds, length)	(	\
	__builtin_constant_p((bounds) < (length)) &&	\
	(bounds) < (length)				\
)

/**
 * strncpy - Copy a string to memory with non-guaranteed NUL padding
 *
 * @p: pointer to destination of copy
 * @q: pointer to NUL-terminated source string to copy
 * @size: bytes to write at @p
 *
 * If strlen(@q) >= @size, the copy of @q will stop after @size bytes,
 * and @p will NOT be NUL-terminated
 *
 * If strlen(@q) < @size, following the copy of @q, trailing NUL bytes
 * will be written to @p until @size total bytes have been written.
 *
 * Do not use this function. While FORTIFY_SOURCE tries to avoid
 * over-reads of @q, it cannot defend against writing unterminated
 * results to @p. Using strncpy() remains ambiguous and fragile.
 * Instead, please choose an alternative, so that the expectation
 * of @p's contents is unambiguous:
 *
 * +--------------------+--------------------+------------+
 * | **p** needs to be: | padded to **size** | not padded |
 * +====================+====================+============+
 * |     NUL-terminated | strscpy_pad()      | strscpy()  |
 * +--------------------+--------------------+------------+
 * | not NUL-terminated | strtomem_pad()     | strtomem() |
 * +--------------------+--------------------+------------+
 *
 * Note strscpy*()'s differing return values for detecting truncation,
 * and strtomem*()'s expectation that the destination is marked with
 * __nonstring when it is a character array.
 *
 */
__FORTIFY_INLINE __diagnose_as(__builtin_strncpy, 1, 2, 3)
char *strncpy(char * const POS p, const char *q, __kernel_size_t size)
{
	const size_t p_size = __member_size(p);

	if (__compiletime_lessthan(p_size, size))
		__write_overflow();
	if (p_size < size)
		fortify_panic(__func__);
	return __underlying_strncpy(p, q, size);
}

extern __kernel_size_t __real_strnlen(const char *, __kernel_size_t) __RENAME(strnlen);
/**
 * strnlen - Return bounded count of characters in a NUL-terminated string
 *
 * @p: pointer to NUL-terminated string to count.
 * @maxlen: maximum number of characters to count.
 *
 * Returns number of characters in @p (NOT including the final NUL), or
 * @maxlen, if no NUL has been found up to there.
 *
 */
__FORTIFY_INLINE __kernel_size_t strnlen(const char * const POS p, __kernel_size_t maxlen)
{
	const size_t p_size = __member_size(p);
	const size_t p_len = __compiletime_strlen(p);
	size_t ret;

	/* We can take compile-time actions when maxlen is const. */
	if (__builtin_constant_p(maxlen) && p_len != SIZE_MAX) {
		/* If p is const, we can use its compile-time-known len. */
		if (maxlen >= p_size)
			return p_len;
	}

	/* Do not check characters beyond the end of p. */
	ret = __real_strnlen(p, maxlen < p_size ? maxlen : p_size);
	if (p_size <= ret && maxlen != ret)
		fortify_panic(__func__);
	return ret;
}

/*
 * Defined after fortified strnlen to reuse it. However, it must still be
 * possible for strlen() to be used on compile-time strings for use in
 * static initializers (i.e. as a constant expression).
 */
/**
 * strlen - Return count of characters in a NUL-terminated string
 *
 * @p: pointer to NUL-terminated string to count.
 *
 * Do not use this function unless the string length is known at
 * compile-time. When @p is unterminated, this function may crash
 * or return unexpected counts that could lead to memory content
 * exposures. Prefer strnlen().
 *
 * Returns number of characters in @p (NOT including the final NUL).
 *
 */
#define strlen(p)							\
	__builtin_choose_expr(__is_constexpr(__builtin_strlen(p)),	\
		__builtin_strlen(p), __fortify_strlen(p))
__FORTIFY_INLINE __diagnose_as(__builtin_strlen, 1)
__kernel_size_t __fortify_strlen(const char * const POS p)
{
	const size_t p_size = __member_size(p);
	__kernel_size_t ret;

	/* Give up if we don't know how large p is. */
	if (p_size == SIZE_MAX)
		return __underlying_strlen(p);
	ret = strnlen(p, p_size);
	if (p_size <= ret)
		fortify_panic(__func__);
	return ret;
}

/* Defined after fortified strlen() to reuse it. */
extern size_t __real_strlcpy(char *, const char *, size_t) __RENAME(strlcpy);
/**
 * strlcpy - Copy a string into another string buffer
 *
 * @p: pointer to destination of copy
 * @q: pointer to NUL-terminated source string to copy
 * @size: maximum number of bytes to write at @p
 *
 * If strlen(@q) >= @size, the copy of @q will be truncated at
 * @size - 1 bytes. @p will always be NUL-terminated.
 *
 * Do not use this function. While FORTIFY_SOURCE tries to avoid
 * over-reads when calculating strlen(@q), it is still possible.
 * Prefer strscpy(), though note its different return values for
 * detecting truncation.
 *
 * Returns total number of bytes written to @p, including terminating NUL.
 *
 */
__FORTIFY_INLINE size_t strlcpy(char * const POS p, const char * const POS q, size_t size)
{
	const size_t p_size = __member_size(p);
	const size_t q_size = __member_size(q);
	size_t q_len;	/* Full count of source string length. */
	size_t len;	/* Count of characters going into destination. */

	if (p_size == SIZE_MAX && q_size == SIZE_MAX)
		return __real_strlcpy(p, q, size);
	q_len = strlen(q);
	len = (q_len >= size) ? size - 1 : q_len;
	if (__builtin_constant_p(size) && __builtin_constant_p(q_len) && size) {
		/* Write size is always larger than destination. */
		if (len >= p_size)
			__write_overflow();
	}
	if (size) {
		if (len >= p_size)
			fortify_panic(__func__);
		__underlying_memcpy(p, q, len);
		p[len] = '\0';
	}
	return q_len;
}

/* Defined after fortified strnlen() to reuse it. */
extern ssize_t __real_strscpy(char *, const char *, size_t) __RENAME(strscpy);
/**
 * strscpy - Copy a C-string into a sized buffer
 *
 * @p: Where to copy the string to
 * @q: Where to copy the string from
 * @size: Size of destination buffer
 *
 * Copy the source string @q, or as much of it as fits, into the destination
 * @p buffer. The behavior is undefined if the string buffers overlap. The
 * destination @p buffer is always NUL terminated, unless it's zero-sized.
 *
 * Preferred to strlcpy() since the API doesn't require reading memory
 * from the source @q string beyond the specified @size bytes, and since
 * the return value is easier to error-check than strlcpy()'s.
 * In addition, the implementation is robust to the string changing out
 * from underneath it, unlike the current strlcpy() implementation.
 *
 * Preferred to strncpy() since it always returns a valid string, and
 * doesn't unnecessarily force the tail of the destination buffer to be
 * zero padded. If padding is desired please use strscpy_pad().
 *
 * Returns the number of characters copied in @p (not including the
 * trailing %NUL) or -E2BIG if @size is 0 or the copy of @q was truncated.
 */
__FORTIFY_INLINE ssize_t strscpy(char * const POS p, const char * const POS q, size_t size)
{
	/* Use string size rather than possible enclosing struct size. */
	const size_t p_size = __member_size(p);
	const size_t q_size = __member_size(q);
	size_t len;

	/* If we cannot get size of p and q default to call strscpy. */
	if (p_size == SIZE_MAX && q_size == SIZE_MAX)
		return __real_strscpy(p, q, size);

	/*
	 * If size can be known at compile time and is greater than
	 * p_size, generate a compile time write overflow error.
	 */
	if (__compiletime_lessthan(p_size, size))
		__write_overflow();

	/* Short-circuit for compile-time known-safe lengths. */
	if (__compiletime_lessthan(p_size, SIZE_MAX)) {
		len = __compiletime_strlen(q);

		if (len < SIZE_MAX && __compiletime_lessthan(len, size)) {
			__underlying_memcpy(p, q, len + 1);
			return len;
		}
	}

	/*
	 * This call protects from read overflow, because len will default to q
	 * length if it smaller than size.
	 */
	len = strnlen(q, size);
	/*
	 * If len equals size, we will copy only size bytes which leads to
	 * -E2BIG being returned.
	 * Otherwise we will copy len + 1 because of the final '\O'.
	 */
	len = len == size ? size : len + 1;

	/*
	 * Generate a runtime write overflow error if len is greater than
	 * p_size.
	 */
	if (len > p_size)
		fortify_panic(__func__);

	/*
	 * We can now safely call vanilla strscpy because we are protected from:
	 * 1. Read overflow thanks to call to strnlen().
	 * 2. Write overflow thanks to above ifs.
	 */
	return __real_strscpy(p, q, len);
}

/* Defined after fortified strlen() to reuse it. */
extern size_t __real_strlcat(char *p, const char *q, size_t avail) __RENAME(strlcat);
/**
 * strlcat - Append a string to an existing string
 *
 * @p: pointer to %NUL-terminated string to append to
 * @q: pointer to %NUL-terminated string to append from
 * @avail: Maximum bytes available in @p
 *
 * Appends %NUL-terminated string @q after the %NUL-terminated
 * string at @p, but will not write beyond @avail bytes total,
 * potentially truncating the copy from @q. @p will stay
 * %NUL-terminated only if a %NUL already existed within
 * the @avail bytes of @p. If so, the resulting number of
 * bytes copied from @q will be at most "@avail - strlen(@p) - 1".
 *
 * Do not use this function. While FORTIFY_SOURCE tries to avoid
 * read and write overflows, this is only possible when the sizes
 * of @p and @q are known to the compiler. Prefer building the
 * string with formatting, via scnprintf(), seq_buf, or similar.
 *
 * Returns total bytes that _would_ have been contained by @p
 * regardless of truncation, similar to snprintf(). If return
 * value is >= @avail, the string has been truncated.
 *
 */
__FORTIFY_INLINE
size_t strlcat(char * const POS p, const char * const POS q, size_t avail)
{
	const size_t p_size = __member_size(p);
	const size_t q_size = __member_size(q);
	size_t p_len, copy_len;
	size_t actual, wanted;

	/* Give up immediately if both buffer sizes are unknown. */
	if (p_size == SIZE_MAX && q_size == SIZE_MAX)
		return __real_strlcat(p, q, avail);

	p_len = strnlen(p, avail);
	copy_len = strlen(q);
	wanted = actual = p_len + copy_len;

	/* Cannot append any more: report truncation. */
	if (avail <= p_len)
		return wanted;

	/* Give up if string is already overflowed. */
	if (p_size <= p_len)
		fortify_panic(__func__);

	if (actual >= avail) {
		copy_len = avail - p_len - 1;
		actual = p_len + copy_len;
	}

	/* Give up if copy will overflow. */
	if (p_size <= actual)
		fortify_panic(__func__);
	__underlying_memcpy(p + p_len, q, copy_len);
	p[actual] = '\0';

	return wanted;
}

/* Defined after fortified strlcat() to reuse it. */
/**
 * strcat - Append a string to an existing string
 *
 * @p: pointer to NUL-terminated string to append to
 * @q: pointer to NUL-terminated source string to append from
 *
 * Do not use this function. While FORTIFY_SOURCE tries to avoid
 * read and write overflows, this is only possible when the
 * destination buffer size is known to the compiler. Prefer
 * building the string with formatting, via scnprintf() or similar.
 * At the very least, use strncat().
 *
 * Returns @p.
 *
 */
__FORTIFY_INLINE __diagnose_as(__builtin_strcat, 1, 2)
char *strcat(char * const POS p, const char *q)
{
	const size_t p_size = __member_size(p);

	if (strlcat(p, q, p_size) >= p_size)
		fortify_panic(__func__);
	return p;
}

/**
 * strncat - Append a string to an existing string
 *
 * @p: pointer to NUL-terminated string to append to
 * @q: pointer to source string to append from
 * @count: Maximum bytes to read from @q
 *
 * Appends at most @count bytes from @q (stopping at the first
 * NUL byte) after the NUL-terminated string at @p. @p will be
 * NUL-terminated.
 *
 * Do not use this function. While FORTIFY_SOURCE tries to avoid
 * read and write overflows, this is only possible when the sizes
 * of @p and @q are known to the compiler. Prefer building the
 * string with formatting, via scnprintf() or similar.
 *
 * Returns @p.
 *
 */
/* Defined after fortified strlen() and strnlen() to reuse them. */
__FORTIFY_INLINE __diagnose_as(__builtin_strncat, 1, 2, 3)
char *strncat(char * const POS p, const char * const POS q, __kernel_size_t count)
{
	const size_t p_size = __member_size(p);
	const size_t q_size = __member_size(q);
	size_t p_len, copy_len;

	if (p_size == SIZE_MAX && q_size == SIZE_MAX)
		return __underlying_strncat(p, q, count);
	p_len = strlen(p);
	copy_len = strnlen(q, count);
	if (p_size < p_len + copy_len + 1)
		fortify_panic(__func__);
	__underlying_memcpy(p + p_len, q, copy_len);
	p[p_len + copy_len] = '\0';
	return p;
}

__FORTIFY_INLINE void fortify_memset_chk(__kernel_size_t size,
					 const size_t p_size,
					 const size_t p_size_field)
{
	if (__builtin_constant_p(size)) {
		/*
		 * Length argument is a constant expression, so we
		 * can perform compile-time bounds checking where
		 * buffer sizes are also known at compile time.
		 */

		/* Error when size is larger than enclosing struct. */
		if (__compiletime_lessthan(p_size_field, p_size) &&
		    __compiletime_lessthan(p_size, size))
			__write_overflow();

		/* Warn when write size is larger than dest field. */
		if (__compiletime_lessthan(p_size_field, size))
			__write_overflow_field(p_size_field, size);
	}
	/*
	 * At this point, length argument may not be a constant expression,
	 * so run-time bounds checking can be done where buffer sizes are
	 * known. (This is not an "else" because the above checks may only
	 * be compile-time warnings, and we want to still warn for run-time
	 * overflows.)
	 */

	/*
	 * Always stop accesses beyond the struct that contains the
	 * field, when the buffer's remaining size is known.
	 * (The SIZE_MAX test is to optimize away checks where the buffer
	 * lengths are unknown.)
	 */
	if (p_size != SIZE_MAX && p_size < size)
		fortify_panic("memset");
}

#define __fortify_memset_chk(p, c, size, p_size, p_size_field) ({	\
	size_t __fortify_size = (size_t)(size);				\
	fortify_memset_chk(__fortify_size, p_size, p_size_field),	\
	__underlying_memset(p, c, __fortify_size);			\
})

/*
 * __struct_size() vs __member_size() must be captured here to avoid
 * evaluating argument side-effects further into the macro layers.
 */
#ifndef CONFIG_KMSAN
#define memset(p, c, s) __fortify_memset_chk(p, c, s,			\
		__struct_size(p), __member_size(p))
#endif

/*
 * To make sure the compiler can enforce protection against buffer overflows,
 * memcpy(), memmove(), and memset() must not be used beyond individual
 * struct members. If you need to copy across multiple members, please use
 * struct_group() to create a named mirror of an anonymous struct union.
 * (e.g. see struct sk_buff.) Read overflow checking is currently only
 * done when a write overflow is also present, or when building with W=1.
 *
 * Mitigation coverage matrix
 *					Bounds checking at:
 *					+-------+-------+-------+-------+
 *					| Compile time  |   Run time    |
 * memcpy() argument sizes:		| write | read  | write | read  |
 *        dest     source   length      +-------+-------+-------+-------+
 * memcpy(known,   known,   constant)	|   y   |   y   |  n/a  |  n/a  |
 * memcpy(known,   unknown, constant)	|   y   |   n   |  n/a  |   V   |
 * memcpy(known,   known,   dynamic)	|   n   |   n   |   B   |   B   |
 * memcpy(known,   unknown, dynamic)	|   n   |   n   |   B   |   V   |
 * memcpy(unknown, known,   constant)	|   n   |   y   |   V   |  n/a  |
 * memcpy(unknown, unknown, constant)	|   n   |   n   |   V   |   V   |
 * memcpy(unknown, known,   dynamic)	|   n   |   n   |   V   |   B   |
 * memcpy(unknown, unknown, dynamic)	|   n   |   n   |   V   |   V   |
 *					+-------+-------+-------+-------+
 *
 * y = perform deterministic compile-time bounds checking
 * n = cannot perform deterministic compile-time bounds checking
 * n/a = no run-time bounds checking needed since compile-time deterministic
 * B = can perform run-time bounds checking (currently unimplemented)
 * V = vulnerable to run-time overflow (will need refactoring to solve)
 *
 */
__FORTIFY_INLINE bool fortify_memcpy_chk(__kernel_size_t size,
					 const size_t p_size,
					 const size_t q_size,
					 const size_t p_size_field,
					 const size_t q_size_field,
					 const char *func)
{
	if (__builtin_constant_p(size)) {
		/*
		 * Length argument is a constant expression, so we
		 * can perform compile-time bounds checking where
		 * buffer sizes are also known at compile time.
		 */

		/* Error when size is larger than enclosing struct. */
		if (__compiletime_lessthan(p_size_field, p_size) &&
		    __compiletime_lessthan(p_size, size))
			__write_overflow();
		if (__compiletime_lessthan(q_size_field, q_size) &&
		    __compiletime_lessthan(q_size, size))
			__read_overflow2();

		/* Warn when write size argument larger than dest field. */
		if (__compiletime_lessthan(p_size_field, size))
			__write_overflow_field(p_size_field, size);
		/*
		 * Warn for source field over-read when building with W=1
		 * or when an over-write happened, so both can be fixed at
		 * the same time.
		 */
		if ((IS_ENABLED(KBUILD_EXTRA_WARN1) ||
		     __compiletime_lessthan(p_size_field, size)) &&
		    __compiletime_lessthan(q_size_field, size))
			__read_overflow2_field(q_size_field, size);
	}
	/*
	 * At this point, length argument may not be a constant expression,
	 * so run-time bounds checking can be done where buffer sizes are
	 * known. (This is not an "else" because the above checks may only
	 * be compile-time warnings, and we want to still warn for run-time
	 * overflows.)
	 */

	/*
	 * Always stop accesses beyond the struct that contains the
	 * field, when the buffer's remaining size is known.
	 * (The SIZE_MAX test is to optimize away checks where the buffer
	 * lengths are unknown.)
	 */
	if ((p_size != SIZE_MAX && p_size < size) ||
	    (q_size != SIZE_MAX && q_size < size))
		fortify_panic(func);

	/*
	 * Warn when writing beyond destination field size.
	 *
	 * We must ignore p_size_field == 0 for existing 0-element
	 * fake flexible arrays, until they are all converted to
	 * proper flexible arrays.
	 *
	 * The implementation of __builtin_*object_size() behaves
	 * like sizeof() when not directly referencing a flexible
	 * array member, which means there will be many bounds checks
	 * that will appear at run-time, without a way for them to be
	 * detected at compile-time (as can be done when the destination
	 * is specifically the flexible array member).
	 * https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101832
	 */
	if (p_size_field != 0 && p_size_field != SIZE_MAX &&
	    p_size != p_size_field && p_size_field < size)
		return true;

	return false;
}

#define __fortify_memcpy_chk(p, q, size, p_size, q_size,		\
			     p_size_field, q_size_field, op) ({		\
	const size_t __fortify_size = (size_t)(size);			\
	const size_t __p_size = (p_size);				\
	const size_t __q_size = (q_size);				\
	const size_t __p_size_field = (p_size_field);			\
	const size_t __q_size_field = (q_size_field);			\
	WARN_ONCE(fortify_memcpy_chk(__fortify_size, __p_size,		\
				     __q_size, __p_size_field,		\
				     __q_size_field, #op),		\
		  #op ": detected field-spanning write (size %zu) of single %s (size %zu)\n", \
		  __fortify_size,					\
		  "field \"" #p "\" at " __FILE__ ":" __stringify(__LINE__), \
		  __p_size_field);					\
	__underlying_##op(p, q, __fortify_size);			\
})

/*
 * Notes about compile-time buffer size detection:
 *
 * With these types...
 *
 *	struct middle {
 *		u16 a;
 *		u8 middle_buf[16];
 *		int b;
 *	};
 *	struct end {
 *		u16 a;
 *		u8 end_buf[16];
 *	};
 *	struct flex {
 *		int a;
 *		u8 flex_buf[];
 *	};
 *
 *	void func(TYPE *ptr) { ... }
 *
 * Cases where destination size cannot be currently detected:
 * - the size of ptr's object (seemingly by design, gcc & clang fail):
 *	__builtin_object_size(ptr, 1) == SIZE_MAX
 * - the size of flexible arrays in ptr's obj (by design, dynamic size):
 *	__builtin_object_size(ptr->flex_buf, 1) == SIZE_MAX
 * - the size of ANY array at the end of ptr's obj (gcc and clang bug):
 *	__builtin_object_size(ptr->end_buf, 1) == SIZE_MAX
 *	https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101836
 *
 * Cases where destination size is currently detected:
 * - the size of non-array members within ptr's object:
 *	__builtin_object_size(ptr->a, 1) == 2
 * - the size of non-flexible-array in the middle of ptr's obj:
 *	__builtin_object_size(ptr->middle_buf, 1) == 16
 *
 */

/*
 * __struct_size() vs __member_size() must be captured here to avoid
 * evaluating argument side-effects further into the macro layers.
 */
#define memcpy(p, q, s)  __fortify_memcpy_chk(p, q, s,			\
		__struct_size(p), __struct_size(q),			\
		__member_size(p), __member_size(q),			\
		memcpy)
#define memmove(p, q, s)  __fortify_memcpy_chk(p, q, s,			\
		__struct_size(p), __struct_size(q),			\
		__member_size(p), __member_size(q),			\
		memmove)

extern void *__real_memscan(void *, int, __kernel_size_t) __RENAME(memscan);
__FORTIFY_INLINE void *memscan(void * const POS0 p, int c, __kernel_size_t size)
{
	const size_t p_size = __struct_size(p);

	if (__compiletime_lessthan(p_size, size))
		__read_overflow();
	if (p_size < size)
		fortify_panic(__func__);
	return __real_memscan(p, c, size);
}

__FORTIFY_INLINE __diagnose_as(__builtin_memcmp, 1, 2, 3)
int memcmp(const void * const POS0 p, const void * const POS0 q, __kernel_size_t size)
{
	const size_t p_size = __struct_size(p);
	const size_t q_size = __struct_size(q);

	if (__builtin_constant_p(size)) {
		if (__compiletime_lessthan(p_size, size))
			__read_overflow();
		if (__compiletime_lessthan(q_size, size))
			__read_overflow2();
	}
	if (p_size < size || q_size < size)
		fortify_panic(__func__);
	return __underlying_memcmp(p, q, size);
}

__FORTIFY_INLINE __diagnose_as(__builtin_memchr, 1, 2, 3)
void *memchr(const void * const POS0 p, int c, __kernel_size_t size)
{
	const size_t p_size = __struct_size(p);

	if (__compiletime_lessthan(p_size, size))
		__read_overflow();
	if (p_size < size)
		fortify_panic(__func__);
	return __underlying_memchr(p, c, size);
}

void *__real_memchr_inv(const void *s, int c, size_t n) __RENAME(memchr_inv);
__FORTIFY_INLINE void *memchr_inv(const void * const POS0 p, int c, size_t size)
{
	const size_t p_size = __struct_size(p);

	if (__compiletime_lessthan(p_size, size))
		__read_overflow();
	if (p_size < size)
		fortify_panic(__func__);
	return __real_memchr_inv(p, c, size);
}

extern void *__real_kmemdup(const void *src, size_t len, gfp_t gfp) __RENAME(kmemdup)
								    __realloc_size(2);
__FORTIFY_INLINE void *kmemdup(const void * const POS0 p, size_t size, gfp_t gfp)
{
	const size_t p_size = __struct_size(p);

	if (__compiletime_lessthan(p_size, size))
		__read_overflow();
	if (p_size < size)
		fortify_panic(__func__);
	return __real_kmemdup(p, size, gfp);
}

/**
 * strcpy - Copy a string into another string buffer
 *
 * @p: pointer to destination of copy
 * @q: pointer to NUL-terminated source string to copy
 *
 * Do not use this function. While FORTIFY_SOURCE tries to avoid
 * overflows, this is only possible when the sizes of @q and @p are
 * known to the compiler. Prefer strscpy(), though note its different
 * return values for detecting truncation.
 *
 * Returns @p.
 *
 */
/* Defined after fortified strlen to reuse it. */
__FORTIFY_INLINE __diagnose_as(__builtin_strcpy, 1, 2)
char *strcpy(char * const POS p, const char * const POS q)
{
	const size_t p_size = __member_size(p);
	const size_t q_size = __member_size(q);
	size_t size;

	/* If neither buffer size is known, immediately give up. */
	if (__builtin_constant_p(p_size) &&
	    __builtin_constant_p(q_size) &&
	    p_size == SIZE_MAX && q_size == SIZE_MAX)
		return __underlying_strcpy(p, q);
	size = strlen(q) + 1;
	/* Compile-time check for const size overflow. */
	if (__compiletime_lessthan(p_size, size))
		__write_overflow();
	/* Run-time check for dynamic size overflow. */
	if (p_size < size)
		fortify_panic(__func__);
	__underlying_memcpy(p, q, size);
	return p;
}

/* Don't use these outside the FORITFY_SOURCE implementation */
#undef __underlying_memchr
#undef __underlying_memcmp
#undef __underlying_strcat
#undef __underlying_strcpy
#undef __underlying_strlen
#undef __underlying_strncat
#undef __underlying_strncpy

#undef POS
#undef POS0

#endif /* _LINUX_FORTIFY_STRING_H_ */