1 // Copyright (c) 2020 Google LLC
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License");
4 // you may not use this file except in compliance with the License.
5 // You may obtain a copy of the License at
6 //
7 // http://www.apache.org/licenses/LICENSE-2.0
8 //
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS,
11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 // See the License for the specific language governing permissions and
13 // limitations under the License.
14
15 #include "source/fuzz/fuzzer_pass_add_stores.h"
16
17 #include "source/fuzz/fuzzer_util.h"
18 #include "source/fuzz/transformation_store.h"
19
20 namespace spvtools {
21 namespace fuzz {
22
FuzzerPassAddStores(opt::IRContext * ir_context,TransformationContext * transformation_context,FuzzerContext * fuzzer_context,protobufs::TransformationSequence * transformations)23 FuzzerPassAddStores::FuzzerPassAddStores(
24 opt::IRContext* ir_context, TransformationContext* transformation_context,
25 FuzzerContext* fuzzer_context,
26 protobufs::TransformationSequence* transformations)
27 : FuzzerPass(ir_context, transformation_context, fuzzer_context,
28 transformations) {}
29
Apply()30 void FuzzerPassAddStores::Apply() {
31 ForEachInstructionWithInstructionDescriptor(
32 [this](opt::Function* function, opt::BasicBlock* block,
33 opt::BasicBlock::iterator inst_it,
34 const protobufs::InstructionDescriptor& instruction_descriptor)
35 -> void {
36 assert(inst_it->opcode() ==
37 instruction_descriptor.target_instruction_opcode() &&
38 "The opcode of the instruction we might insert before must be "
39 "the same as the opcode in the descriptor for the instruction");
40
41 // Check whether it is legitimate to insert a store before this
42 // instruction.
43 if (!fuzzerutil::CanInsertOpcodeBeforeInstruction(SpvOpStore,
44 inst_it)) {
45 return;
46 }
47
48 // Randomly decide whether to try inserting a store here.
49 if (!GetFuzzerContext()->ChoosePercentage(
50 GetFuzzerContext()->GetChanceOfAddingStore())) {
51 return;
52 }
53
54 // Look for pointers we might consider storing to.
55 std::vector<opt::Instruction*> relevant_pointers =
56 FindAvailableInstructions(
57 function, block, inst_it,
58 [this, block](opt::IRContext* context,
59 opt::Instruction* instruction) -> bool {
60 if (!instruction->result_id() || !instruction->type_id()) {
61 return false;
62 }
63 auto type_inst = context->get_def_use_mgr()->GetDef(
64 instruction->type_id());
65 if (type_inst->opcode() != SpvOpTypePointer) {
66 // Not a pointer.
67 return false;
68 }
69 if (instruction->IsReadOnlyPointer()) {
70 // Read only: cannot store to it.
71 return false;
72 }
73 switch (instruction->opcode()) {
74 case SpvOpConstantNull:
75 case SpvOpUndef:
76 // Do not allow storing to a null or undefined pointer;
77 // this might be OK if the block is dead, but for now we
78 // conservatively avoid it.
79 return false;
80 default:
81 break;
82 }
83 return GetTransformationContext()
84 ->GetFactManager()
85 ->BlockIsDead(block->id()) ||
86 GetTransformationContext()
87 ->GetFactManager()
88 ->PointeeValueIsIrrelevant(
89 instruction->result_id());
90 });
91
92 // At this point, |relevant_pointers| contains all the pointers we might
93 // think of storing to.
94 if (relevant_pointers.empty()) {
95 return;
96 }
97
98 auto pointer = relevant_pointers[GetFuzzerContext()->RandomIndex(
99 relevant_pointers)];
100
101 std::vector<opt::Instruction*> relevant_values =
102 FindAvailableInstructions(
103 function, block, inst_it,
104 [pointer](opt::IRContext* context,
105 opt::Instruction* instruction) -> bool {
106 if (!instruction->result_id() || !instruction->type_id()) {
107 return false;
108 }
109 return instruction->type_id() ==
110 context->get_def_use_mgr()
111 ->GetDef(pointer->type_id())
112 ->GetSingleWordInOperand(1);
113 });
114
115 if (relevant_values.empty()) {
116 return;
117 }
118
119 // Choose a value at random, and create and apply a storing
120 // transformation based on it and the pointer.
121 ApplyTransformation(TransformationStore(
122 pointer->result_id(),
123 relevant_values[GetFuzzerContext()->RandomIndex(relevant_values)]
124 ->result_id(),
125 instruction_descriptor));
126 });
127 }
128
129 } // namespace fuzz
130 } // namespace spvtools
131