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