Merge branch 'next' into for-linus
[linux-2.6-microblaze.git] / kernel / kcsan / encoding.h
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 /* Bitmasks for the encoded watchpoint access information. */
41 #define WATCHPOINT_WRITE_MASK   BIT(BITS_PER_LONG-1)
42 #define WATCHPOINT_SIZE_MASK    GENMASK(BITS_PER_LONG-2, WATCHPOINT_ADDR_BITS)
43 #define WATCHPOINT_ADDR_MASK    GENMASK(WATCHPOINT_ADDR_BITS-1, 0)
44 static_assert(WATCHPOINT_ADDR_MASK == (1UL << WATCHPOINT_ADDR_BITS) - 1);
45 static_assert((WATCHPOINT_WRITE_MASK ^ WATCHPOINT_SIZE_MASK ^ WATCHPOINT_ADDR_MASK) == ~0UL);
46
47 static inline bool check_encodable(unsigned long addr, size_t size)
48 {
49         /*
50          * While we can encode addrs<PAGE_SIZE, avoid crashing with a NULL
51          * pointer deref inside KCSAN.
52          */
53         return addr >= PAGE_SIZE && size <= MAX_ENCODABLE_SIZE;
54 }
55
56 static inline long
57 encode_watchpoint(unsigned long addr, size_t size, bool is_write)
58 {
59         return (long)((is_write ? WATCHPOINT_WRITE_MASK : 0) |
60                       (size << WATCHPOINT_ADDR_BITS) |
61                       (addr & WATCHPOINT_ADDR_MASK));
62 }
63
64 static __always_inline bool decode_watchpoint(long watchpoint,
65                                               unsigned long *addr_masked,
66                                               size_t *size,
67                                               bool *is_write)
68 {
69         if (watchpoint == INVALID_WATCHPOINT ||
70             watchpoint == CONSUMED_WATCHPOINT)
71                 return false;
72
73         *addr_masked =    (unsigned long)watchpoint & WATCHPOINT_ADDR_MASK;
74         *size        =   ((unsigned long)watchpoint & WATCHPOINT_SIZE_MASK) >> WATCHPOINT_ADDR_BITS;
75         *is_write    = !!((unsigned long)watchpoint & WATCHPOINT_WRITE_MASK);
76
77         return true;
78 }
79
80 /*
81  * Return watchpoint slot for an address.
82  */
83 static __always_inline int watchpoint_slot(unsigned long addr)
84 {
85         return (addr / PAGE_SIZE) % CONFIG_KCSAN_NUM_WATCHPOINTS;
86 }
87
88 static __always_inline bool matching_access(unsigned long addr1, size_t size1,
89                                             unsigned long addr2, size_t size2)
90 {
91         unsigned long end_range1 = addr1 + size1 - 1;
92         unsigned long end_range2 = addr2 + size2 - 1;
93
94         return addr1 <= end_range2 && addr2 <= end_range1;
95 }
96
97 #endif /* _KERNEL_KCSAN_ENCODING_H */