1//===-- dfsan_origin.h ----------------------------------*- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This file is a part of DataFlowSanitizer.
10//
11// Origin id utils.
12//===----------------------------------------------------------------------===//
13
14#ifndef DFSAN_ORIGIN_H
15#define DFSAN_ORIGIN_H
16
17#include "dfsan_chained_origin_depot.h"
18#include "dfsan_flags.h"
19#include "sanitizer_common/sanitizer_stackdepot.h"
20
21namespace __dfsan {
22
23// Origin handling.
24//
25// Origin is a 32-bit identifier that is attached to any taint value in the
26// program and describes how this memory came to be tainted.
27//
28// Chained origin id is like:
29// zzzz xxxx xxxx xxxx
30//
31// Chained origin id describes an event of storing a taint value to
32// memory. The xxx part is a value of ChainedOriginDepot, which is a mapping of
33// (stack_id, prev_id) -> id, where
34//  * stack_id describes the event.
35//    StackDepot keeps a mapping between those and corresponding stack traces.
36//  * prev_id is another origin id that describes the earlier part of the
37//    taint value history. 0 prev_id indicates the start of a chain.
38// Following a chain of prev_id provides the full recorded history of a taint
39// value.
40//
41// This, effectively, defines a forest where nodes are points in value history
42// marked with origin ids, and edges are events that are marked with stack_id.
43//
44// The "zzzz" bits of chained origin id are used to store the length of the
45// origin chain.
46
47class Origin {
48 public:
49  static bool isValidId(u32 id) { return id != 0; }
50
51  u32 raw_id() const { return raw_id_; }
52
53  bool isChainedOrigin() const { return Origin::isValidId(raw_id_); }
54
55  u32 getChainedId() const {
56    CHECK(Origin::isValidId(raw_id_));
57    return raw_id_ & kChainedIdMask;
58  }
59
60  // Returns the next origin in the chain and the current stack trace.
61  //
62  // It scans a partition of StackDepot linearly, and is used only by origin
63  // tracking report.
64  Origin getNextChainedOrigin(StackTrace *stack) const {
65    CHECK(Origin::isValidId(raw_id_));
66    u32 prev_id;
67    u32 stack_id = GetChainedOriginDepot()->Get(getChainedId(), &prev_id);
68    if (stack)
69      *stack = StackDepotGet(stack_id);
70    return Origin(prev_id);
71  }
72
73  static Origin CreateChainedOrigin(Origin prev, StackTrace *stack) {
74    int depth = prev.isChainedOrigin() ? prev.depth() : -1;
75    // depth is the length of the chain minus 1.
76    // origin_history_size of 0 means unlimited depth.
77    if (flags().origin_history_size > 0) {
78      ++depth;
79      if (depth >= flags().origin_history_size || depth > kMaxDepth)
80        return prev;
81    }
82
83    StackDepotHandle h = StackDepotPut_WithHandle(*stack);
84    if (!h.valid())
85      return prev;
86
87    if (flags().origin_history_per_stack_limit > 0) {
88      int use_count = h.use_count();
89      if (use_count > flags().origin_history_per_stack_limit)
90        return prev;
91    }
92
93    u32 chained_id;
94    bool inserted =
95        GetChainedOriginDepot()->Put(h.id(), prev.raw_id(), &chained_id);
96    CHECK((chained_id & kChainedIdMask) == chained_id);
97
98    if (inserted && flags().origin_history_per_stack_limit > 0)
99      h.inc_use_count_unsafe();
100
101    return Origin((depth << kDepthShift) | chained_id);
102  }
103
104  static Origin FromRawId(u32 id) { return Origin(id); }
105
106 private:
107  static const int kDepthBits = 4;
108  static const int kDepthShift = 32 - kDepthBits;
109
110  static const u32 kChainedIdMask = ((u32)-1) >> kDepthBits;
111
112  u32 raw_id_;
113
114  explicit Origin(u32 raw_id) : raw_id_(raw_id) {}
115
116  int depth() const {
117    CHECK(isChainedOrigin());
118    return (raw_id_ >> kDepthShift) & ((1 << kDepthBits) - 1);
119  }
120
121 public:
122  static const int kMaxDepth = (1 << kDepthBits) - 1;
123};
124
125}  // namespace __dfsan
126
127#endif  // DFSAN_ORIGIN_H
128