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