kernel/kcsan/encoding.h

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