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 */ 98