LXR linux/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
  49static inline bool check_encodable(unsigned long addr, size_t size)
  50{
  51        return size <= MAX_ENCODABLE_SIZE;
  52}
  53
  54static inline long
  55encode_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
  62static __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 */
  81static __always_inline int watchpoint_slot(unsigned long addr)
  82{
  83        return (addr / PAGE_SIZE) % CONFIG_KCSAN_NUM_WATCHPOINTS;
  84}
  85
  86static __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 */
  96