1 /*
2 * Copyright (C) 2014 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 #include "fault_handler.h"
18
19 #include <sys/ucontext.h>
20
21 #include "art_method.h"
22 #include "base/enums.h"
23 #include "base/hex_dump.h"
24 #include "base/logging.h" // For VLOG.
25 #include "base/macros.h"
26 #include "globals.h"
27 #include "registers_arm64.h"
28 #include "thread-current-inl.h"
29
30 extern "C" void art_quick_throw_stack_overflow();
31 extern "C" void art_quick_throw_null_pointer_exception_from_signal();
32 extern "C" void art_quick_implicit_suspend();
33
34 //
35 // ARM64 specific fault handler functions.
36 //
37
38 namespace art {
39
GetMethodAndReturnPcAndSp(siginfo_t * siginfo ATTRIBUTE_UNUSED,void * context,ArtMethod ** out_method,uintptr_t * out_return_pc,uintptr_t * out_sp)40 void FaultManager::GetMethodAndReturnPcAndSp(siginfo_t* siginfo ATTRIBUTE_UNUSED, void* context,
41 ArtMethod** out_method,
42 uintptr_t* out_return_pc, uintptr_t* out_sp) {
43 struct ucontext *uc = reinterpret_cast<struct ucontext *>(context);
44 struct sigcontext *sc = reinterpret_cast<struct sigcontext*>(&uc->uc_mcontext);
45 *out_sp = static_cast<uintptr_t>(sc->sp);
46 VLOG(signals) << "sp: " << *out_sp;
47 if (*out_sp == 0) {
48 return;
49 }
50
51 // In the case of a stack overflow, the stack is not valid and we can't
52 // get the method from the top of the stack. However it's in x0.
53 uintptr_t* fault_addr = reinterpret_cast<uintptr_t*>(sc->fault_address);
54 uintptr_t* overflow_addr = reinterpret_cast<uintptr_t*>(
55 reinterpret_cast<uint8_t*>(*out_sp) - GetStackOverflowReservedBytes(InstructionSet::kArm64));
56 if (overflow_addr == fault_addr) {
57 *out_method = reinterpret_cast<ArtMethod*>(sc->regs[0]);
58 } else {
59 // The method is at the top of the stack.
60 *out_method = *reinterpret_cast<ArtMethod**>(*out_sp);
61 }
62
63 // Work out the return PC. This will be the address of the instruction
64 // following the faulting ldr/str instruction.
65 VLOG(signals) << "pc: " << std::hex
66 << static_cast<void*>(reinterpret_cast<uint8_t*>(sc->pc));
67
68 *out_return_pc = sc->pc + 4;
69 }
70
Action(int sig ATTRIBUTE_UNUSED,siginfo_t * info,void * context)71 bool NullPointerHandler::Action(int sig ATTRIBUTE_UNUSED, siginfo_t* info, void* context) {
72 if (!IsValidImplicitCheck(info)) {
73 return false;
74 }
75 // The code that looks for the catch location needs to know the value of the
76 // PC at the point of call. For Null checks we insert a GC map that is immediately after
77 // the load/store instruction that might cause the fault.
78
79 struct ucontext *uc = reinterpret_cast<struct ucontext*>(context);
80 struct sigcontext *sc = reinterpret_cast<struct sigcontext*>(&uc->uc_mcontext);
81
82 // Push the gc map location to the stack and pass the fault address in LR.
83 sc->sp -= sizeof(uintptr_t);
84 *reinterpret_cast<uintptr_t*>(sc->sp) = sc->pc + 4;
85 sc->regs[30] = reinterpret_cast<uintptr_t>(info->si_addr);
86
87 sc->pc = reinterpret_cast<uintptr_t>(art_quick_throw_null_pointer_exception_from_signal);
88 VLOG(signals) << "Generating null pointer exception";
89 return true;
90 }
91
92 // A suspend check is done using the following instruction sequence:
93 // 0xf7223228: f9405640 ldr x0, [x18, #168]
94 // .. some intervening instructions
95 // 0xf7223230: f9400000 ldr x0, [x0]
96
97 // The offset from r18 is Thread::ThreadSuspendTriggerOffset().
98 // To check for a suspend check, we examine the instructions that caused
99 // the fault (at PC-4 and PC).
Action(int sig ATTRIBUTE_UNUSED,siginfo_t * info ATTRIBUTE_UNUSED,void * context)100 bool SuspensionHandler::Action(int sig ATTRIBUTE_UNUSED, siginfo_t* info ATTRIBUTE_UNUSED,
101 void* context) {
102 // These are the instructions to check for. The first one is the ldr x0,[r18,#xxx]
103 // where xxx is the offset of the suspend trigger.
104 uint32_t checkinst1 = 0xf9400240 |
105 (Thread::ThreadSuspendTriggerOffset<PointerSize::k64>().Int32Value() << 7);
106 uint32_t checkinst2 = 0xf9400000;
107
108 struct ucontext *uc = reinterpret_cast<struct ucontext *>(context);
109 struct sigcontext *sc = reinterpret_cast<struct sigcontext*>(&uc->uc_mcontext);
110 uint8_t* ptr2 = reinterpret_cast<uint8_t*>(sc->pc);
111 uint8_t* ptr1 = ptr2 - 4;
112 VLOG(signals) << "checking suspend";
113
114 uint32_t inst2 = *reinterpret_cast<uint32_t*>(ptr2);
115 VLOG(signals) << "inst2: " << std::hex << inst2 << " checkinst2: " << checkinst2;
116 if (inst2 != checkinst2) {
117 // Second instruction is not good, not ours.
118 return false;
119 }
120
121 // The first instruction can a little bit up the stream due to load hoisting
122 // in the compiler.
123 uint8_t* limit = ptr1 - 80; // Compiler will hoist to a max of 20 instructions.
124 bool found = false;
125 while (ptr1 > limit) {
126 uint32_t inst1 = *reinterpret_cast<uint32_t*>(ptr1);
127 VLOG(signals) << "inst1: " << std::hex << inst1 << " checkinst1: " << checkinst1;
128 if (inst1 == checkinst1) {
129 found = true;
130 break;
131 }
132 ptr1 -= 4;
133 }
134 if (found) {
135 VLOG(signals) << "suspend check match";
136 // This is a suspend check. Arrange for the signal handler to return to
137 // art_quick_implicit_suspend. Also set LR so that after the suspend check it
138 // will resume the instruction (current PC + 4). PC points to the
139 // ldr x0,[x0,#0] instruction (r0 will be 0, set by the trigger).
140
141 sc->regs[30] = sc->pc + 4;
142 sc->pc = reinterpret_cast<uintptr_t>(art_quick_implicit_suspend);
143
144 // Now remove the suspend trigger that caused this fault.
145 Thread::Current()->RemoveSuspendTrigger();
146 VLOG(signals) << "removed suspend trigger invoking test suspend";
147 return true;
148 }
149 return false;
150 }
151
Action(int sig ATTRIBUTE_UNUSED,siginfo_t * info ATTRIBUTE_UNUSED,void * context)152 bool StackOverflowHandler::Action(int sig ATTRIBUTE_UNUSED, siginfo_t* info ATTRIBUTE_UNUSED,
153 void* context) {
154 struct ucontext *uc = reinterpret_cast<struct ucontext *>(context);
155 struct sigcontext *sc = reinterpret_cast<struct sigcontext*>(&uc->uc_mcontext);
156 VLOG(signals) << "stack overflow handler with sp at " << std::hex << &uc;
157 VLOG(signals) << "sigcontext: " << std::hex << sc;
158
159 uintptr_t sp = sc->sp;
160 VLOG(signals) << "sp: " << std::hex << sp;
161
162 uintptr_t fault_addr = sc->fault_address;
163 VLOG(signals) << "fault_addr: " << std::hex << fault_addr;
164 VLOG(signals) << "checking for stack overflow, sp: " << std::hex << sp <<
165 ", fault_addr: " << fault_addr;
166
167 uintptr_t overflow_addr = sp - GetStackOverflowReservedBytes(InstructionSet::kArm64);
168
169 // Check that the fault address is the value expected for a stack overflow.
170 if (fault_addr != overflow_addr) {
171 VLOG(signals) << "Not a stack overflow";
172 return false;
173 }
174
175 VLOG(signals) << "Stack overflow found";
176
177 // Now arrange for the signal handler to return to art_quick_throw_stack_overflow.
178 // The value of LR must be the same as it was when we entered the code that
179 // caused this fault. This will be inserted into a callee save frame by
180 // the function to which this handler returns (art_quick_throw_stack_overflow).
181 sc->pc = reinterpret_cast<uintptr_t>(art_quick_throw_stack_overflow);
182
183 // The kernel will now return to the address in sc->pc.
184 return true;
185 }
186 } // namespace art
187
188