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 check_encodable(unsigned long addr,size_t size)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 encode_watchpoint(unsigned long addr,size_t size,bool is_write)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 decode_watchpoint(long watchpoint,unsigned long * addr_masked,size_t * size,bool * is_write)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 */ watchpoint_slot(unsigned long addr)88 static __always_inline int watchpoint_slot(unsigned long addr) 89 { 90 return (addr / PAGE_SIZE) % CONFIG_KCSAN_NUM_WATCHPOINTS; 91 } 92 matching_access(unsigned long addr1,size_t size1,unsigned long addr2,size_t size2)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