1 | /* SPDX-License-Identifier: GPL-2.0 */ |
2 | /* |
3 | * KCSAN watchpoint encoding. |
4 | * |
5 | * Copyright (C) 2019, Google LLC. |
6 | */ |
7 | |
8 | #ifndef _KERNEL_KCSAN_ENCODING_H |
9 | #define _KERNEL_KCSAN_ENCODING_H |
10 | |
11 | #include <linux/bits.h> |
12 | #include <linux/log2.h> |
13 | #include <linux/mm.h> |
14 | |
15 | #include "kcsan.h" |
16 | |
17 | #define SLOT_RANGE PAGE_SIZE |
18 | |
19 | #define INVALID_WATCHPOINT 0 |
20 | #define CONSUMED_WATCHPOINT 1 |
21 | |
22 | /* |
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. |
25 | */ |
26 | #define MAX_ENCODABLE_SIZE (SLOT_RANGE * (1 + KCSAN_CHECK_ADJACENT)) |
27 | |
28 | /* |
29 | * Number of bits we use to store size info. |
30 | */ |
31 | #define WATCHPOINT_SIZE_BITS bits_per(MAX_ENCODABLE_SIZE) |
32 | /* |
33 | * This encoding for addresses discards the upper (1 for is-write + SIZE_BITS); |
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 observable 2 things need to happen: |
36 | * |
37 | * 1. different addresses but with the same encoded address race; |
38 | * 2. and both map onto the same watchpoint slots; |
39 | * |
40 | * Both these are assumed to be very unlikely. However, in case it still |
41 | * happens, the report logic will filter out the false positive (see report.c). |
42 | */ |
43 | #define WATCHPOINT_ADDR_BITS (BITS_PER_LONG-1 - WATCHPOINT_SIZE_BITS) |
44 | |
45 | /* Bitmasks for the encoded watchpoint access information. */ |
46 | #define WATCHPOINT_WRITE_MASK BIT(BITS_PER_LONG-1) |
47 | #define WATCHPOINT_SIZE_MASK GENMASK(BITS_PER_LONG-2, WATCHPOINT_ADDR_BITS) |
48 | #define WATCHPOINT_ADDR_MASK GENMASK(WATCHPOINT_ADDR_BITS-1, 0) |
49 | static_assert(WATCHPOINT_ADDR_MASK == (1UL << WATCHPOINT_ADDR_BITS) - 1); |
50 | static_assert((WATCHPOINT_WRITE_MASK ^ WATCHPOINT_SIZE_MASK ^ WATCHPOINT_ADDR_MASK) == ~0UL); |
51 | |
52 | static inline bool check_encodable(unsigned long addr, size_t size) |
53 | { |
54 | /* |
55 | * While we can encode addrs<PAGE_SIZE, avoid crashing with a NULL |
56 | * pointer deref inside KCSAN. |
57 | */ |
58 | return addr >= PAGE_SIZE && size <= MAX_ENCODABLE_SIZE; |
59 | } |
60 | |
61 | static inline long |
62 | encode_watchpoint(unsigned long addr, size_t size, bool is_write) |
63 | { |
64 | return (long)((is_write ? WATCHPOINT_WRITE_MASK : 0) | |
65 | (size << WATCHPOINT_ADDR_BITS) | |
66 | (addr & WATCHPOINT_ADDR_MASK)); |
67 | } |
68 | |
69 | static __always_inline bool decode_watchpoint(long watchpoint, |
70 | unsigned long *addr_masked, |
71 | size_t *size, |
72 | bool *is_write) |
73 | { |
74 | if (watchpoint == INVALID_WATCHPOINT || |
75 | watchpoint == CONSUMED_WATCHPOINT) |
76 | return false; |
77 | |
78 | *addr_masked = (unsigned long)watchpoint & WATCHPOINT_ADDR_MASK; |
79 | *size = ((unsigned long)watchpoint & WATCHPOINT_SIZE_MASK) >> WATCHPOINT_ADDR_BITS; |
80 | *is_write = !!((unsigned long)watchpoint & WATCHPOINT_WRITE_MASK); |
81 | |
82 | return true; |
83 | } |
84 | |
85 | /* |
86 | * Return watchpoint slot for an address. |
87 | */ |
88 | static __always_inline int watchpoint_slot(unsigned long addr) |
89 | { |
90 | return (addr / PAGE_SIZE) % CONFIG_KCSAN_NUM_WATCHPOINTS; |
91 | } |
92 | |
93 | static __always_inline bool matching_access(unsigned long addr1, size_t size1, |
94 | unsigned long addr2, size_t size2) |
95 | { |
96 | unsigned long end_range1 = addr1 + size1 - 1; |
97 | unsigned long end_range2 = addr2 + size2 - 1; |
98 | |
99 | return addr1 <= end_range2 && addr2 <= end_range1; |
100 | } |
101 | |
102 | #endif /* _KERNEL_KCSAN_ENCODING_H */ |
103 | |