1 /*
2 * Copyright (C) 2023 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 "arch/instruction_set.h"
22 #include "base/logging.h" // For VLOG.
23
24 extern "C" void art_quick_throw_stack_overflow();
25 extern "C" void art_quick_throw_null_pointer_exception_from_signal();
26 extern "C" void art_quick_implicit_suspend();
27
28 // RISCV64 specific fault handler functions (or stubs if unimplemented yet).
29
30 namespace art HIDDEN {
31
GetFaultPc(siginfo_t *,void * context)32 uintptr_t FaultManager::GetFaultPc(siginfo_t*, void* context) {
33 ucontext_t* uc = reinterpret_cast<ucontext_t*>(context);
34 mcontext_t* mc = reinterpret_cast<mcontext_t*>(&uc->uc_mcontext);
35 if (mc->__gregs[REG_SP] == 0) {
36 VLOG(signals) << "Missing SP";
37 return 0u;
38 }
39 return mc->__gregs[REG_PC];
40 }
41
GetFaultSp(void * context)42 uintptr_t FaultManager::GetFaultSp(void* context) {
43 ucontext_t* uc = reinterpret_cast<ucontext_t*>(context);
44 mcontext_t* mc = reinterpret_cast<mcontext_t*>(&uc->uc_mcontext);
45 return mc->__gregs[REG_SP];
46 }
47
Action(int sig,siginfo_t * info,void * context)48 bool NullPointerHandler::Action([[maybe_unused]] int sig, siginfo_t* info, void* context) {
49 uintptr_t fault_address = reinterpret_cast<uintptr_t>(info->si_addr);
50 if (!IsValidFaultAddress(fault_address)) {
51 return false;
52 }
53
54 ucontext_t* uc = reinterpret_cast<ucontext_t*>(context);
55 mcontext_t* mc = reinterpret_cast<mcontext_t*>(&uc->uc_mcontext);
56 ArtMethod** sp = reinterpret_cast<ArtMethod**>(mc->__gregs[REG_SP]);
57 if (!IsValidMethod(*sp)) {
58 return false;
59 }
60
61 // For null checks in compiled code we insert a stack map that is immediately
62 // after the load/store instruction that might cause the fault and we need to
63 // pass the return PC to the handler. For null checks in Nterp, we similarly
64 // need the return PC to recognize that this was a null check in Nterp, so
65 // that the handler can get the needed data from the Nterp frame.
66
67 // Need to work out the size of the instruction that caused the exception.
68 uintptr_t old_pc = mc->__gregs[REG_PC];
69 uintptr_t instr_size = (reinterpret_cast<uint16_t*>(old_pc)[0] & 3u) == 3u ? 4u : 2u;
70 uintptr_t return_pc = old_pc + instr_size;
71 if (!IsValidReturnPc(sp, return_pc)) {
72 return false;
73 }
74
75 // Push the return PC to the stack and pass the fault address in RA.
76 mc->__gregs[REG_SP] -= sizeof(uintptr_t);
77 *reinterpret_cast<uintptr_t*>(mc->__gregs[REG_SP]) = return_pc;
78 mc->__gregs[REG_RA] = fault_address;
79
80 // Arrange for the signal handler to return to the NPE entrypoint.
81 mc->__gregs[REG_PC] =
82 reinterpret_cast<uintptr_t>(art_quick_throw_null_pointer_exception_from_signal);
83 VLOG(signals) << "Generating null pointer exception";
84 return true;
85 }
86
Action(int,siginfo_t *,void *)87 bool SuspensionHandler::Action(int, siginfo_t*, void*) {
88 LOG(FATAL) << "SuspensionHandler::Action is not implemented for RISC-V";
89 return false;
90 }
91
Action(int sig,siginfo_t * info,void * context)92 bool StackOverflowHandler::Action([[maybe_unused]] int sig,
93 siginfo_t* info,
94 void* context) {
95 ucontext_t* uc = reinterpret_cast<ucontext_t*>(context);
96 mcontext_t* mc = reinterpret_cast<mcontext_t*>(&uc->uc_mcontext);
97 VLOG(signals) << "stack overflow handler with sp at " << std::hex << &uc;
98 VLOG(signals) << "sigcontext: " << std::hex << mc;
99
100 uintptr_t sp = mc->__gregs[REG_SP];
101 VLOG(signals) << "sp: " << std::hex << sp;
102
103 uintptr_t fault_addr = reinterpret_cast<uintptr_t>(info->si_addr);
104 VLOG(signals) << "fault_addr: " << std::hex << fault_addr;
105 VLOG(signals) << "checking for stack overflow, sp: " << std::hex << sp <<
106 ", fault_addr: " << fault_addr;
107
108 uintptr_t overflow_addr = sp - GetStackOverflowReservedBytes(InstructionSet::kRiscv64);
109
110 // Check that the fault address is the value expected for a stack overflow.
111 if (fault_addr != overflow_addr) {
112 VLOG(signals) << "Not a stack overflow";
113 return false;
114 }
115
116 VLOG(signals) << "Stack overflow found";
117
118 // Now arrange for the signal handler to return to art_quick_throw_stack_overflow.
119 // The value of RA must be the same as it was when we entered the code that
120 // caused this fault. This will be inserted into a callee save frame by
121 // the function to which this handler returns (art_quick_throw_stack_overflow).
122 mc->__gregs[REG_PC] = reinterpret_cast<uintptr_t>(art_quick_throw_stack_overflow);
123
124 // The kernel will now return to the address in `mc->__gregs[REG_PC]`.
125 return true;
126 }
127
128 } // namespace art
129