1 /* SPDX-License-Identifier: GPL-2.0 */ 1 /* SPDX-License-Identifier: GPL-2.0 */
2 /* 2 /*
3 * KCSAN watchpoint encoding. 3 * KCSAN watchpoint encoding.
4 * 4 *
5 * Copyright (C) 2019, Google LLC. 5 * Copyright (C) 2019, Google LLC.
6 */ 6 */
7 7
8 #ifndef _KERNEL_KCSAN_ENCODING_H 8 #ifndef _KERNEL_KCSAN_ENCODING_H
9 #define _KERNEL_KCSAN_ENCODING_H 9 #define _KERNEL_KCSAN_ENCODING_H
10 10
11 #include <linux/bits.h> 11 #include <linux/bits.h>
12 #include <linux/log2.h> 12 #include <linux/log2.h>
13 #include <linux/mm.h> 13 #include <linux/mm.h>
14 14
15 #include "kcsan.h" 15 #include "kcsan.h"
16 16
17 #define SLOT_RANGE PAGE_SIZE 17 #define SLOT_RANGE PAGE_SIZE
18 18
19 #define INVALID_WATCHPOINT 0 19 #define INVALID_WATCHPOINT 0
20 #define CONSUMED_WATCHPOINT 1 20 #define CONSUMED_WATCHPOINT 1
21 21
22 /* 22 /*
23 * The maximum useful size of accesses for whi 23 * The maximum useful size of accesses for which we set up watchpoints is the
24 * max range of slots we check on an access. 24 * max range of slots we check on an access.
25 */ 25 */
26 #define MAX_ENCODABLE_SIZE (SLOT_RANGE * (1 + 26 #define MAX_ENCODABLE_SIZE (SLOT_RANGE * (1 + KCSAN_CHECK_ADJACENT))
27 27
28 /* 28 /*
29 * Number of bits we use to store size info. 29 * Number of bits we use to store size info.
30 */ 30 */
31 #define WATCHPOINT_SIZE_BITS bits_per(MAX_ENCO 31 #define WATCHPOINT_SIZE_BITS bits_per(MAX_ENCODABLE_SIZE)
32 /* 32 /*
33 * This encoding for addresses discards the up 33 * This encoding for addresses discards the upper (1 for is-write + SIZE_BITS);
34 * however, most 64-bit architectures do not u 34 * however, most 64-bit architectures do not use the full 64-bit address space.
35 * Also, in order for a false positive to be o 35 * Also, in order for a false positive to be observable 2 things need to happen:
36 * 36 *
37 * 1. different addresses but with the sa 37 * 1. different addresses but with the same encoded address race;
38 * 2. and both map onto the same watchpoi 38 * 2. and both map onto the same watchpoint slots;
39 * 39 *
40 * Both these are assumed to be very unlikely. 40 * Both these are assumed to be very unlikely. However, in case it still
41 * happens, the report logic will filter out t 41 * happens, the report logic will filter out the false positive (see report.c).
42 */ 42 */
43 #define WATCHPOINT_ADDR_BITS (BITS_PER_LONG-1 43 #define WATCHPOINT_ADDR_BITS (BITS_PER_LONG-1 - WATCHPOINT_SIZE_BITS)
44 44
45 /* Bitmasks for the encoded watchpoint access 45 /* Bitmasks for the encoded watchpoint access information. */
46 #define WATCHPOINT_WRITE_MASK BIT(BITS_PER_L 46 #define WATCHPOINT_WRITE_MASK BIT(BITS_PER_LONG-1)
47 #define WATCHPOINT_SIZE_MASK GENMASK(BITS_P 47 #define WATCHPOINT_SIZE_MASK GENMASK(BITS_PER_LONG-2, WATCHPOINT_ADDR_BITS)
48 #define WATCHPOINT_ADDR_MASK GENMASK(WATCHP 48 #define WATCHPOINT_ADDR_MASK GENMASK(WATCHPOINT_ADDR_BITS-1, 0)
49 static_assert(WATCHPOINT_ADDR_MASK == (1UL << 49 static_assert(WATCHPOINT_ADDR_MASK == (1UL << WATCHPOINT_ADDR_BITS) - 1);
50 static_assert((WATCHPOINT_WRITE_MASK ^ WATCHPO 50 static_assert((WATCHPOINT_WRITE_MASK ^ WATCHPOINT_SIZE_MASK ^ WATCHPOINT_ADDR_MASK) == ~0UL);
51 51
52 static inline bool check_encodable(unsigned lo 52 static inline bool check_encodable(unsigned long addr, size_t size)
53 { 53 {
54 /* 54 /*
55 * While we can encode addrs<PAGE_SIZE 55 * While we can encode addrs<PAGE_SIZE, avoid crashing with a NULL
56 * pointer deref inside KCSAN. 56 * pointer deref inside KCSAN.
57 */ 57 */
58 return addr >= PAGE_SIZE && size <= MA 58 return addr >= PAGE_SIZE && size <= MAX_ENCODABLE_SIZE;
59 } 59 }
60 60
61 static inline long 61 static inline long
62 encode_watchpoint(unsigned long addr, size_t s 62 encode_watchpoint(unsigned long addr, size_t size, bool is_write)
63 { 63 {
64 return (long)((is_write ? WATCHPOINT_W 64 return (long)((is_write ? WATCHPOINT_WRITE_MASK : 0) |
65 (size << WATCHPOINT_ADDR 65 (size << WATCHPOINT_ADDR_BITS) |
66 (addr & WATCHPOINT_ADDR_ 66 (addr & WATCHPOINT_ADDR_MASK));
67 } 67 }
68 68
69 static __always_inline bool decode_watchpoint( 69 static __always_inline bool decode_watchpoint(long watchpoint,
70 70 unsigned long *addr_masked,
71 71 size_t *size,
72 72 bool *is_write)
73 { 73 {
74 if (watchpoint == INVALID_WATCHPOINT | 74 if (watchpoint == INVALID_WATCHPOINT ||
75 watchpoint == CONSUMED_WATCHPOINT) 75 watchpoint == CONSUMED_WATCHPOINT)
76 return false; 76 return false;
77 77
78 *addr_masked = (unsigned long)watch 78 *addr_masked = (unsigned long)watchpoint & WATCHPOINT_ADDR_MASK;
79 *size = ((unsigned long)watch 79 *size = ((unsigned long)watchpoint & WATCHPOINT_SIZE_MASK) >> WATCHPOINT_ADDR_BITS;
80 *is_write = !!((unsigned long)watch 80 *is_write = !!((unsigned long)watchpoint & WATCHPOINT_WRITE_MASK);
81 81
82 return true; 82 return true;
83 } 83 }
84 84
85 /* 85 /*
86 * Return watchpoint slot for an address. 86 * Return watchpoint slot for an address.
87 */ 87 */
88 static __always_inline int watchpoint_slot(uns 88 static __always_inline int watchpoint_slot(unsigned long addr)
89 { 89 {
90 return (addr / PAGE_SIZE) % CONFIG_KCS 90 return (addr / PAGE_SIZE) % CONFIG_KCSAN_NUM_WATCHPOINTS;
91 } 91 }
92 92
93 static __always_inline bool matching_access(un 93 static __always_inline bool matching_access(unsigned long addr1, size_t size1,
94 un 94 unsigned long addr2, size_t size2)
95 { 95 {
96 unsigned long end_range1 = addr1 + siz 96 unsigned long end_range1 = addr1 + size1 - 1;
97 unsigned long end_range2 = addr2 + siz 97 unsigned long end_range2 = addr2 + size2 - 1;
98 98
99 return addr1 <= end_range2 && addr2 <= 99 return addr1 <= end_range2 && addr2 <= end_range1;
100 } 100 }
101 101
102 #endif /* _KERNEL_KCSAN_ENCODING_H */ 102 #endif /* _KERNEL_KCSAN_ENCODING_H */
103 103
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