1 /* SPDX-License-Identifier: GPL-2.0 */
2
3 #ifndef _KERNEL_KCSAN_ENCODING_H
4 #define _KERNEL_KCSAN_ENCODING_H
5
6 #include <linux/bits.h>
7 #include <linux/log2.h>
8 #include <linux/mm.h>
9
10 #include "kcsan.h"
11
12 #define SLOT_RANGE PAGE_SIZE
13
14 #define INVALID_WATCHPOINT 0
15 #define CONSUMED_WATCHPOINT 1
16
17 /*
18 * The maximum useful size of accesses for which we set up watchpoints is the
19 * max range of slots we check on an access.
20 */
21 #define MAX_ENCODABLE_SIZE (SLOT_RANGE * (1 + KCSAN_CHECK_ADJACENT))
22
23 /*
24 * Number of bits we use to store size info.
25 */
26 #define WATCHPOINT_SIZE_BITS bits_per(MAX_ENCODABLE_SIZE)
27 /*
28 * This encoding for addresses discards the upper (1 for is-write + SIZE_BITS);
29 * however, most 64-bit architectures do not use the full 64-bit address space.
30 * Also, in order for a false positive to be observable 2 things need to happen:
31 *
32 * 1. different addresses but with the same encoded address race;
33 * 2. and both map onto the same watchpoint slots;
34 *
35 * Both these are assumed to be very unlikely. However, in case it still
36 * happens, the report logic will filter out the false positive (see report.c).
37 */
38 #define WATCHPOINT_ADDR_BITS (BITS_PER_LONG-1 - WATCHPOINT_SIZE_BITS)
39
40 /*
41 * Masks to set/retrieve the encoded data.
42 */
43 #define WATCHPOINT_WRITE_MASK BIT(BITS_PER_LONG-1)
44 #define WATCHPOINT_SIZE_MASK \
45 GENMASK(BITS_PER_LONG-2, BITS_PER_LONG-2 - WATCHPOINT_SIZE_BITS)
46 #define WATCHPOINT_ADDR_MASK \
47 GENMASK(BITS_PER_LONG-3 - WATCHPOINT_SIZE_BITS, 0)
48
check_encodable(unsigned long addr,size_t size)49 static inline bool check_encodable(unsigned long addr, size_t size)
50 {
51 return size <= MAX_ENCODABLE_SIZE;
52 }
53
54 static inline long
encode_watchpoint(unsigned long addr,size_t size,bool is_write)55 encode_watchpoint(unsigned long addr, size_t size, bool is_write)
56 {
57 return (long)((is_write ? WATCHPOINT_WRITE_MASK : 0) |
58 (size << WATCHPOINT_ADDR_BITS) |
59 (addr & WATCHPOINT_ADDR_MASK));
60 }
61
decode_watchpoint(long watchpoint,unsigned long * addr_masked,size_t * size,bool * is_write)62 static __always_inline bool decode_watchpoint(long watchpoint,
63 unsigned long *addr_masked,
64 size_t *size,
65 bool *is_write)
66 {
67 if (watchpoint == INVALID_WATCHPOINT ||
68 watchpoint == CONSUMED_WATCHPOINT)
69 return false;
70
71 *addr_masked = (unsigned long)watchpoint & WATCHPOINT_ADDR_MASK;
72 *size = ((unsigned long)watchpoint & WATCHPOINT_SIZE_MASK) >> WATCHPOINT_ADDR_BITS;
73 *is_write = !!((unsigned long)watchpoint & WATCHPOINT_WRITE_MASK);
74
75 return true;
76 }
77
78 /*
79 * Return watchpoint slot for an address.
80 */
watchpoint_slot(unsigned long addr)81 static __always_inline int watchpoint_slot(unsigned long addr)
82 {
83 return (addr / PAGE_SIZE) % CONFIG_KCSAN_NUM_WATCHPOINTS;
84 }
85
matching_access(unsigned long addr1,size_t size1,unsigned long addr2,size_t size2)86 static __always_inline bool matching_access(unsigned long addr1, size_t size1,
87 unsigned long addr2, size_t size2)
88 {
89 unsigned long end_range1 = addr1 + size1 - 1;
90 unsigned long end_range2 = addr2 + size2 - 1;
91
92 return addr1 <= end_range2 && addr2 <= end_range1;
93 }
94
95 #endif /* _KERNEL_KCSAN_ENCODING_H */
96
