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 #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 "thread-current-inl.h" 28 29 // 30 // ARM specific fault handler functions. 31 // 32 33 namespace art { 34 35 extern "C" void art_quick_throw_null_pointer_exception_from_signal(); 36 extern "C" void art_quick_throw_stack_overflow(); 37 extern "C" void art_quick_implicit_suspend(); 38 39 // Get the size of a thumb2 instruction in bytes. 40 static uint32_t GetInstructionSize(uint8_t* pc) { 41 uint16_t instr = pc[0] | pc[1] << 8; 42 bool is_32bit = ((instr & 0xF000) == 0xF000) || ((instr & 0xF800) == 0xE800); 43 uint32_t instr_size = is_32bit ? 4 : 2; 44 return instr_size; 45 } 46 47 void FaultManager::GetMethodAndReturnPcAndSp(siginfo_t* siginfo ATTRIBUTE_UNUSED, void* context, 48 ArtMethod** out_method, 49 uintptr_t* out_return_pc, uintptr_t* out_sp) { 50 struct ucontext* uc = reinterpret_cast<struct ucontext*>(context); 51 struct sigcontext *sc = reinterpret_cast<struct sigcontext*>(&uc->uc_mcontext); 52 *out_sp = static_cast<uintptr_t>(sc->arm_sp); 53 VLOG(signals) << "sp: " << std::hex << *out_sp; 54 if (*out_sp == 0) { 55 return; 56 } 57 58 // In the case of a stack overflow, the stack is not valid and we can't 59 // get the method from the top of the stack. However it's in r0. 60 uintptr_t* fault_addr = reinterpret_cast<uintptr_t*>(sc->fault_address); 61 uintptr_t* overflow_addr = reinterpret_cast<uintptr_t*>( 62 reinterpret_cast<uint8_t*>(*out_sp) - GetStackOverflowReservedBytes(InstructionSet::kArm)); 63 if (overflow_addr == fault_addr) { 64 *out_method = reinterpret_cast<ArtMethod*>(sc->arm_r0); 65 } else { 66 // The method is at the top of the stack. 67 *out_method = reinterpret_cast<ArtMethod*>(reinterpret_cast<uintptr_t*>(*out_sp)[0]); 68 } 69 70 // Work out the return PC. This will be the address of the instruction 71 // following the faulting ldr/str instruction. This is in thumb mode so 72 // the instruction might be a 16 or 32 bit one. Also, the GC map always 73 // has the bottom bit of the PC set so we also need to set that. 74 75 // Need to work out the size of the instruction that caused the exception. 76 uint8_t* ptr = reinterpret_cast<uint8_t*>(sc->arm_pc); 77 VLOG(signals) << "pc: " << std::hex << static_cast<void*>(ptr); 78 79 if (ptr == nullptr) { 80 // Somebody jumped to 0x0. Definitely not ours, and will definitely segfault below. 81 *out_method = nullptr; 82 return; 83 } 84 85 uint32_t instr_size = GetInstructionSize(ptr); 86 87 *out_return_pc = (sc->arm_pc + instr_size) | 1; 88 } 89 90 bool NullPointerHandler::Action(int sig ATTRIBUTE_UNUSED, siginfo_t* info, void* context) { 91 if (!IsValidImplicitCheck(info)) { 92 return false; 93 } 94 // The code that looks for the catch location needs to know the value of the 95 // ARM PC at the point of call. For Null checks we insert a GC map that is immediately after 96 // the load/store instruction that might cause the fault. However the mapping table has 97 // the low bits set for thumb mode so we need to set the bottom bit for the LR 98 // register in order to find the mapping. 99 100 // Need to work out the size of the instruction that caused the exception. 101 struct ucontext *uc = reinterpret_cast<struct ucontext*>(context); 102 struct sigcontext *sc = reinterpret_cast<struct sigcontext*>(&uc->uc_mcontext); 103 uint8_t* ptr = reinterpret_cast<uint8_t*>(sc->arm_pc); 104 uint32_t instr_size = GetInstructionSize(ptr); 105 uintptr_t gc_map_location = (sc->arm_pc + instr_size) | 1; 106 107 // Push the gc map location to the stack and pass the fault address in LR. 108 sc->arm_sp -= sizeof(uintptr_t); 109 *reinterpret_cast<uintptr_t*>(sc->arm_sp) = gc_map_location; 110 sc->arm_lr = reinterpret_cast<uintptr_t>(info->si_addr); 111 sc->arm_pc = reinterpret_cast<uintptr_t>(art_quick_throw_null_pointer_exception_from_signal); 112 // Pass the faulting address as the first argument of 113 // art_quick_throw_null_pointer_exception_from_signal. 114 VLOG(signals) << "Generating null pointer exception"; 115 return true; 116 } 117 118 // A suspend check is done using the following instruction sequence: 119 // 0xf723c0b2: f8d902c0 ldr.w r0, [r9, #704] ; suspend_trigger_ 120 // .. some intervening instruction 121 // 0xf723c0b6: 6800 ldr r0, [r0, #0] 122 123 // The offset from r9 is Thread::ThreadSuspendTriggerOffset(). 124 // To check for a suspend check, we examine the instructions that caused 125 // the fault (at PC-4 and PC). 126 bool SuspensionHandler::Action(int sig ATTRIBUTE_UNUSED, siginfo_t* info ATTRIBUTE_UNUSED, 127 void* context) { 128 // These are the instructions to check for. The first one is the ldr r0,[r9,#xxx] 129 // where xxx is the offset of the suspend trigger. 130 uint32_t checkinst1 = 0xf8d90000 131 + Thread::ThreadSuspendTriggerOffset<PointerSize::k32>().Int32Value(); 132 uint16_t checkinst2 = 0x6800; 133 134 struct ucontext* uc = reinterpret_cast<struct ucontext*>(context); 135 struct sigcontext *sc = reinterpret_cast<struct sigcontext*>(&uc->uc_mcontext); 136 uint8_t* ptr2 = reinterpret_cast<uint8_t*>(sc->arm_pc); 137 uint8_t* ptr1 = ptr2 - 4; 138 VLOG(signals) << "checking suspend"; 139 140 uint16_t inst2 = ptr2[0] | ptr2[1] << 8; 141 VLOG(signals) << "inst2: " << std::hex << inst2 << " checkinst2: " << checkinst2; 142 if (inst2 != checkinst2) { 143 // Second instruction is not good, not ours. 144 return false; 145 } 146 147 // The first instruction can a little bit up the stream due to load hoisting 148 // in the compiler. 149 uint8_t* limit = ptr1 - 40; // Compiler will hoist to a max of 20 instructions. 150 bool found = false; 151 while (ptr1 > limit) { 152 uint32_t inst1 = ((ptr1[0] | ptr1[1] << 8) << 16) | (ptr1[2] | ptr1[3] << 8); 153 VLOG(signals) << "inst1: " << std::hex << inst1 << " checkinst1: " << checkinst1; 154 if (inst1 == checkinst1) { 155 found = true; 156 break; 157 } 158 ptr1 -= 2; // Min instruction size is 2 bytes. 159 } 160 if (found) { 161 VLOG(signals) << "suspend check match"; 162 // This is a suspend check. Arrange for the signal handler to return to 163 // art_quick_implicit_suspend. Also set LR so that after the suspend check it 164 // will resume the instruction (current PC + 2). PC points to the 165 // ldr r0,[r0,#0] instruction (r0 will be 0, set by the trigger). 166 167 // NB: remember that we need to set the bottom bit of the LR register 168 // to switch to thumb mode. 169 VLOG(signals) << "arm lr: " << std::hex << sc->arm_lr; 170 VLOG(signals) << "arm pc: " << std::hex << sc->arm_pc; 171 sc->arm_lr = sc->arm_pc + 3; // +2 + 1 (for thumb) 172 sc->arm_pc = reinterpret_cast<uintptr_t>(art_quick_implicit_suspend); 173 174 // Now remove the suspend trigger that caused this fault. 175 Thread::Current()->RemoveSuspendTrigger(); 176 VLOG(signals) << "removed suspend trigger invoking test suspend"; 177 return true; 178 } 179 return false; 180 } 181 182 // Stack overflow fault handler. 183 // 184 // This checks that the fault address is equal to the current stack pointer 185 // minus the overflow region size (16K typically). The instruction sequence 186 // that generates this signal is: 187 // 188 // sub r12,sp,#16384 189 // ldr.w r12,[r12,#0] 190 // 191 // The second instruction will fault if r12 is inside the protected region 192 // on the stack. 193 // 194 // If we determine this is a stack overflow we need to move the stack pointer 195 // to the overflow region below the protected region. 196 197 bool StackOverflowHandler::Action(int sig ATTRIBUTE_UNUSED, siginfo_t* info ATTRIBUTE_UNUSED, 198 void* context) { 199 struct ucontext* uc = reinterpret_cast<struct ucontext*>(context); 200 struct sigcontext *sc = reinterpret_cast<struct sigcontext*>(&uc->uc_mcontext); 201 VLOG(signals) << "stack overflow handler with sp at " << std::hex << &uc; 202 VLOG(signals) << "sigcontext: " << std::hex << sc; 203 204 uintptr_t sp = sc->arm_sp; 205 VLOG(signals) << "sp: " << std::hex << sp; 206 207 uintptr_t fault_addr = sc->fault_address; 208 VLOG(signals) << "fault_addr: " << std::hex << fault_addr; 209 VLOG(signals) << "checking for stack overflow, sp: " << std::hex << sp << 210 ", fault_addr: " << fault_addr; 211 212 uintptr_t overflow_addr = sp - GetStackOverflowReservedBytes(InstructionSet::kArm); 213 214 // Check that the fault address is the value expected for a stack overflow. 215 if (fault_addr != overflow_addr) { 216 VLOG(signals) << "Not a stack overflow"; 217 return false; 218 } 219 220 VLOG(signals) << "Stack overflow found"; 221 222 // Now arrange for the signal handler to return to art_quick_throw_stack_overflow_from. 223 // The value of LR must be the same as it was when we entered the code that 224 // caused this fault. This will be inserted into a callee save frame by 225 // the function to which this handler returns (art_quick_throw_stack_overflow). 226 sc->arm_pc = reinterpret_cast<uintptr_t>(art_quick_throw_stack_overflow); 227 228 // The kernel will now return to the address in sc->arm_pc. 229 return true; 230 } 231 } // namespace art 232
