Marco Elver | dfd402a | 2019-11-14 19:02:54 +0100 | [diff] [blame] | 1 | /* SPDX-License-Identifier: GPL-2.0 */ |
Marco Elver | bd0ccc4 | 2021-01-15 18:09:53 +0100 | [diff] [blame] | 2 | /* |
| 3 | * KCSAN watchpoint encoding. |
| 4 | * |
| 5 | * Copyright (C) 2019, Google LLC. |
| 6 | */ |
Marco Elver | dfd402a | 2019-11-14 19:02:54 +0100 | [diff] [blame] | 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 |
Ingo Molnar | 5cbaefe | 2019-11-20 10:41:43 +0100 | [diff] [blame] | 18 | |
| 19 | #define INVALID_WATCHPOINT 0 |
Marco Elver | dfd402a | 2019-11-14 19:02:54 +0100 | [diff] [blame] | 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 | * |
Randy Dunlap | 7b7b8a2 | 2020-10-15 20:10:28 -0700 | [diff] [blame] | 40 | * Both these are assumed to be very unlikely. However, in case it still |
Marco Elver | dfd402a | 2019-11-14 19:02:54 +0100 | [diff] [blame] | 41 | * happens, the report logic will filter out the false positive (see report.c). |
| 42 | */ |
Ingo Molnar | 5cbaefe | 2019-11-20 10:41:43 +0100 | [diff] [blame] | 43 | #define WATCHPOINT_ADDR_BITS (BITS_PER_LONG-1 - WATCHPOINT_SIZE_BITS) |
Marco Elver | dfd402a | 2019-11-14 19:02:54 +0100 | [diff] [blame] | 44 | |
Marco Elver | 1d094ce | 2020-11-06 10:34:56 +0100 | [diff] [blame] | 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); |
Marco Elver | dfd402a | 2019-11-14 19:02:54 +0100 | [diff] [blame] | 51 | |
| 52 | static inline bool check_encodable(unsigned long addr, size_t size) |
| 53 | { |
Marco Elver | 55a2346 | 2020-10-22 13:45:53 +0200 | [diff] [blame] | 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; |
Marco Elver | dfd402a | 2019-11-14 19:02:54 +0100 | [diff] [blame] | 59 | } |
| 60 | |
Ingo Molnar | 5cbaefe | 2019-11-20 10:41:43 +0100 | [diff] [blame] | 61 | static inline long |
| 62 | encode_watchpoint(unsigned long addr, size_t size, bool is_write) |
Marco Elver | dfd402a | 2019-11-14 19:02:54 +0100 | [diff] [blame] | 63 | { |
| 64 | return (long)((is_write ? WATCHPOINT_WRITE_MASK : 0) | |
| 65 | (size << WATCHPOINT_ADDR_BITS) | |
| 66 | (addr & WATCHPOINT_ADDR_MASK)); |
| 67 | } |
| 68 | |
Marco Elver | 5c36142 | 2020-01-07 17:31:04 +0100 | [diff] [blame] | 69 | static __always_inline bool decode_watchpoint(long watchpoint, |
| 70 | unsigned long *addr_masked, |
| 71 | size_t *size, |
| 72 | bool *is_write) |
Marco Elver | dfd402a | 2019-11-14 19:02:54 +0100 | [diff] [blame] | 73 | { |
| 74 | if (watchpoint == INVALID_WATCHPOINT || |
| 75 | watchpoint == CONSUMED_WATCHPOINT) |
| 76 | return false; |
| 77 | |
Ingo Molnar | 5cbaefe | 2019-11-20 10:41:43 +0100 | [diff] [blame] | 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); |
Marco Elver | dfd402a | 2019-11-14 19:02:54 +0100 | [diff] [blame] | 81 | |
| 82 | return true; |
| 83 | } |
| 84 | |
| 85 | /* |
| 86 | * Return watchpoint slot for an address. |
| 87 | */ |
Marco Elver | 5c36142 | 2020-01-07 17:31:04 +0100 | [diff] [blame] | 88 | static __always_inline int watchpoint_slot(unsigned long addr) |
Marco Elver | dfd402a | 2019-11-14 19:02:54 +0100 | [diff] [blame] | 89 | { |
| 90 | return (addr / PAGE_SIZE) % CONFIG_KCSAN_NUM_WATCHPOINTS; |
| 91 | } |
| 92 | |
Marco Elver | 5c36142 | 2020-01-07 17:31:04 +0100 | [diff] [blame] | 93 | static __always_inline bool matching_access(unsigned long addr1, size_t size1, |
| 94 | unsigned long addr2, size_t size2) |
Marco Elver | dfd402a | 2019-11-14 19:02:54 +0100 | [diff] [blame] | 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 */ |