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 happens
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
49static inline bool check_encodable(unsigned long addr, size_t size)
50{
51	return size <= MAX_ENCODABLE_SIZE;
52}
53
54static inline long
55encode_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
62static __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 */
81static __always_inline int watchpoint_slot(unsigned long addr)
82{
83	return (addr / PAGE_SIZE) % CONFIG_KCSAN_NUM_WATCHPOINTS;
84}
85
86static __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 */