1 /*
2 * Copyright (C) 2008 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
18 #include "fault_handler.h"
19
20 #include <sys/ucontext.h>
21 #include "base/macros.h"
22 #include "base/hex_dump.h"
23 #include "globals.h"
24 #include "base/logging.h"
25 #include "base/hex_dump.h"
26 #include "instruction_set.h"
27 #include "mirror/art_method.h"
28 #include "mirror/art_method-inl.h"
29 #include "thread.h"
30 #include "thread-inl.h"
31
32 //
33 // ARM specific fault handler functions.
34 //
35
36 namespace art {
37
38 extern "C" void art_quick_throw_null_pointer_exception();
39 extern "C" void art_quick_throw_stack_overflow();
40 extern "C" void art_quick_implicit_suspend();
41
42 // Get the size of a thumb2 instruction in bytes.
GetInstructionSize(uint8_t * pc)43 static uint32_t GetInstructionSize(uint8_t* pc) {
44 uint16_t instr = pc[0] | pc[1] << 8;
45 bool is_32bit = ((instr & 0xF000) == 0xF000) || ((instr & 0xF800) == 0xE800);
46 uint32_t instr_size = is_32bit ? 4 : 2;
47 return instr_size;
48 }
49
HandleNestedSignal(int sig,siginfo_t * info,void * context)50 void FaultManager::HandleNestedSignal(int sig, siginfo_t* info, void* context) {
51 // Note that in this handler we set up the registers and return to
52 // longjmp directly rather than going through an assembly language stub. The
53 // reason for this is that longjmp is (currently) in ARM mode and that would
54 // require switching modes in the stub - incurring an unwanted relocation.
55
56 struct ucontext *uc = reinterpret_cast<struct ucontext*>(context);
57 struct sigcontext *sc = reinterpret_cast<struct sigcontext*>(&uc->uc_mcontext);
58 Thread* self = Thread::Current();
59 CHECK(self != nullptr); // This will cause a SIGABRT if self is nullptr.
60
61 sc->arm_r0 = reinterpret_cast<uintptr_t>(*self->GetNestedSignalState());
62 sc->arm_r1 = 1;
63 sc->arm_pc = reinterpret_cast<uintptr_t>(longjmp);
64 VLOG(signals) << "longjmp address: " << reinterpret_cast<void*>(sc->arm_pc);
65 }
66
GetMethodAndReturnPcAndSp(siginfo_t * siginfo,void * context,mirror::ArtMethod ** out_method,uintptr_t * out_return_pc,uintptr_t * out_sp)67 void FaultManager::GetMethodAndReturnPcAndSp(siginfo_t* siginfo, void* context,
68 mirror::ArtMethod** out_method,
69 uintptr_t* out_return_pc, uintptr_t* out_sp) {
70 struct ucontext* uc = reinterpret_cast<struct ucontext*>(context);
71 struct sigcontext *sc = reinterpret_cast<struct sigcontext*>(&uc->uc_mcontext);
72 *out_sp = static_cast<uintptr_t>(sc->arm_sp);
73 VLOG(signals) << "sp: " << *out_sp;
74 if (*out_sp == 0) {
75 return;
76 }
77
78 // In the case of a stack overflow, the stack is not valid and we can't
79 // get the method from the top of the stack. However it's in r0.
80 uintptr_t* fault_addr = reinterpret_cast<uintptr_t*>(sc->fault_address);
81 uintptr_t* overflow_addr = reinterpret_cast<uintptr_t*>(
82 reinterpret_cast<uint8_t*>(*out_sp) - GetStackOverflowReservedBytes(kArm));
83 if (overflow_addr == fault_addr) {
84 *out_method = reinterpret_cast<mirror::ArtMethod*>(sc->arm_r0);
85 } else {
86 // The method is at the top of the stack.
87 *out_method = reinterpret_cast<mirror::ArtMethod*>(reinterpret_cast<uintptr_t*>(*out_sp)[0]);
88 }
89
90 // Work out the return PC. This will be the address of the instruction
91 // following the faulting ldr/str instruction. This is in thumb mode so
92 // the instruction might be a 16 or 32 bit one. Also, the GC map always
93 // has the bottom bit of the PC set so we also need to set that.
94
95 // Need to work out the size of the instruction that caused the exception.
96 uint8_t* ptr = reinterpret_cast<uint8_t*>(sc->arm_pc);
97 VLOG(signals) << "pc: " << std::hex << static_cast<void*>(ptr);
98 uint32_t instr_size = GetInstructionSize(ptr);
99
100 *out_return_pc = (sc->arm_pc + instr_size) | 1;
101 }
102
Action(int sig,siginfo_t * info,void * context)103 bool NullPointerHandler::Action(int sig, siginfo_t* info, void* context) {
104 // The code that looks for the catch location needs to know the value of the
105 // ARM PC at the point of call. For Null checks we insert a GC map that is immediately after
106 // the load/store instruction that might cause the fault. However the mapping table has
107 // the low bits set for thumb mode so we need to set the bottom bit for the LR
108 // register in order to find the mapping.
109
110 // Need to work out the size of the instruction that caused the exception.
111 struct ucontext *uc = reinterpret_cast<struct ucontext*>(context);
112 struct sigcontext *sc = reinterpret_cast<struct sigcontext*>(&uc->uc_mcontext);
113 uint8_t* ptr = reinterpret_cast<uint8_t*>(sc->arm_pc);
114
115 uint32_t instr_size = GetInstructionSize(ptr);
116 sc->arm_lr = (sc->arm_pc + instr_size) | 1; // LR needs to point to gc map location
117 sc->arm_pc = reinterpret_cast<uintptr_t>(art_quick_throw_null_pointer_exception);
118 VLOG(signals) << "Generating null pointer exception";
119 return true;
120 }
121
122 // A suspend check is done using the following instruction sequence:
123 // 0xf723c0b2: f8d902c0 ldr.w r0, [r9, #704] ; suspend_trigger_
124 // .. some intervening instruction
125 // 0xf723c0b6: 6800 ldr r0, [r0, #0]
126
127 // The offset from r9 is Thread::ThreadSuspendTriggerOffset().
128 // To check for a suspend check, we examine the instructions that caused
129 // the fault (at PC-4 and PC).
Action(int sig,siginfo_t * info,void * context)130 bool SuspensionHandler::Action(int sig, siginfo_t* info, void* context) {
131 // These are the instructions to check for. The first one is the ldr r0,[r9,#xxx]
132 // where xxx is the offset of the suspend trigger.
133 uint32_t checkinst1 = 0xf8d90000 + Thread::ThreadSuspendTriggerOffset<4>().Int32Value();
134 uint16_t checkinst2 = 0x6800;
135
136 struct ucontext* uc = reinterpret_cast<struct ucontext*>(context);
137 struct sigcontext *sc = reinterpret_cast<struct sigcontext*>(&uc->uc_mcontext);
138 uint8_t* ptr2 = reinterpret_cast<uint8_t*>(sc->arm_pc);
139 uint8_t* ptr1 = ptr2 - 4;
140 VLOG(signals) << "checking suspend";
141
142 uint16_t inst2 = ptr2[0] | ptr2[1] << 8;
143 VLOG(signals) << "inst2: " << std::hex << inst2 << " checkinst2: " << checkinst2;
144 if (inst2 != checkinst2) {
145 // Second instruction is not good, not ours.
146 return false;
147 }
148
149 // The first instruction can a little bit up the stream due to load hoisting
150 // in the compiler.
151 uint8_t* limit = ptr1 - 40; // Compiler will hoist to a max of 20 instructions.
152 bool found = false;
153 while (ptr1 > limit) {
154 uint32_t inst1 = ((ptr1[0] | ptr1[1] << 8) << 16) | (ptr1[2] | ptr1[3] << 8);
155 VLOG(signals) << "inst1: " << std::hex << inst1 << " checkinst1: " << checkinst1;
156 if (inst1 == checkinst1) {
157 found = true;
158 break;
159 }
160 ptr1 -= 2; // Min instruction size is 2 bytes.
161 }
162 if (found) {
163 VLOG(signals) << "suspend check match";
164 // This is a suspend check. Arrange for the signal handler to return to
165 // art_quick_implicit_suspend. Also set LR so that after the suspend check it
166 // will resume the instruction (current PC + 2). PC points to the
167 // ldr r0,[r0,#0] instruction (r0 will be 0, set by the trigger).
168
169 // NB: remember that we need to set the bottom bit of the LR register
170 // to switch to thumb mode.
171 VLOG(signals) << "arm lr: " << std::hex << sc->arm_lr;
172 VLOG(signals) << "arm pc: " << std::hex << sc->arm_pc;
173 sc->arm_lr = sc->arm_pc + 3; // +2 + 1 (for thumb)
174 sc->arm_pc = reinterpret_cast<uintptr_t>(art_quick_implicit_suspend);
175
176 // Now remove the suspend trigger that caused this fault.
177 Thread::Current()->RemoveSuspendTrigger();
178 VLOG(signals) << "removed suspend trigger invoking test suspend";
179 return true;
180 }
181 return false;
182 }
183
184 // Stack overflow fault handler.
185 //
186 // This checks that the fault address is equal to the current stack pointer
187 // minus the overflow region size (16K typically). The instruction sequence
188 // that generates this signal is:
189 //
190 // sub r12,sp,#16384
191 // ldr.w r12,[r12,#0]
192 //
193 // The second instruction will fault if r12 is inside the protected region
194 // on the stack.
195 //
196 // If we determine this is a stack overflow we need to move the stack pointer
197 // to the overflow region below the protected region.
198
Action(int sig,siginfo_t * info,void * context)199 bool StackOverflowHandler::Action(int sig, siginfo_t* info, void* context) {
200 struct ucontext* uc = reinterpret_cast<struct ucontext*>(context);
201 struct sigcontext *sc = reinterpret_cast<struct sigcontext*>(&uc->uc_mcontext);
202 VLOG(signals) << "stack overflow handler with sp at " << std::hex << &uc;
203 VLOG(signals) << "sigcontext: " << std::hex << sc;
204
205 uintptr_t sp = sc->arm_sp;
206 VLOG(signals) << "sp: " << std::hex << sp;
207
208 uintptr_t fault_addr = sc->fault_address;
209 VLOG(signals) << "fault_addr: " << std::hex << fault_addr;
210 VLOG(signals) << "checking for stack overflow, sp: " << std::hex << sp <<
211 ", fault_addr: " << fault_addr;
212
213 uintptr_t overflow_addr = sp - GetStackOverflowReservedBytes(kArm);
214
215 // Check that the fault address is the value expected for a stack overflow.
216 if (fault_addr != overflow_addr) {
217 VLOG(signals) << "Not a stack overflow";
218 return false;
219 }
220
221 VLOG(signals) << "Stack overflow found";
222
223 // Now arrange for the signal handler to return to art_quick_throw_stack_overflow_from.
224 // The value of LR must be the same as it was when we entered the code that
225 // caused this fault. This will be inserted into a callee save frame by
226 // the function to which this handler returns (art_quick_throw_stack_overflow).
227 sc->arm_pc = reinterpret_cast<uintptr_t>(art_quick_throw_stack_overflow);
228
229 // The kernel will now return to the address in sc->arm_pc.
230 return true;
231 }
232 } // namespace art
233