Avoid undefined behavior: member access within misaligned address

Before this change we see the following UBSAN stack trace in Fuchsia:

  #0    0x000020d00518f81a in AcpiRsConvertAmlToResources(UINT8*, UINT32, UINT32, UINT8, void**) ../../third_party/acpica/source/components/resources/rslist.c:104 <platform-bus-x86.so>+0x2cd81a
  #1.2  0x00002348b567277f in ubsan_GetStackTrace() compiler-rt/lib/ubsan/ubsan_diag.cpp:41 <libclang_rt.asan.so>+0x3d77f
  #1.1  0x00002348b567277f in MaybePrintStackTrace() compiler-rt/lib/ubsan/ubsan_diag.cpp:51 <libclang_rt.asan.so>+0x3d77f
  #1    0x00002348b567277f in ~ScopedReport() compiler-rt/lib/ubsan/ubsan_diag.cpp:387 <libclang_rt.asan.so>+0x3d77f
  #2    0x00002348b5673385 in handleTypeMismatchImpl() compiler-rt/lib/ubsan/ubsan_handlers.cpp:137 <libclang_rt.asan.so>+0x3e385
  #3    0x00002348b5672ead in compiler-rt/lib/ubsan/ubsan_handlers.cpp:142 <libclang_rt.asan.so>+0x3dead
  #4    0x000020d00518f81a in AcpiRsConvertAmlToResources(UINT8*, UINT32, UINT32, UINT8, void**) ../../third_party/acpica/source/components/resources/rslist.c:104 <platform-bus-x86.so>+0x2cd81a
  #5    0x000020d0051b8ea9 in AcpiUtWalkAmlResources(ACPI_WALK_STATE*, UINT8*, ACPI_SIZE, ACPI_WALK_AML_CALLBACK, void**) ../../third_party/acpica/source/components/utilities/utresrc.c:234 <platform-bus-x86.so>+0x2f6ea9
  #6    0x000020d00518a806 in AcpiRsCreateResourceList(ACPI_OPERAND_OBJECT*, ACPI_BUFFER*) ../../third_party/acpica/source/components/resources/rscreate.c:199 <platform-bus-x86.so>+0x2c8806
  #7    0x000020d005195ff2 in AcpiRsGetMethodData(ACPI_HANDLE, const char*, ACPI_BUFFER*) ../../third_party/acpica/source/components/resources/rsutils.c:770 <platform-bus-x86.so>+0x2d3ff2
  #8    0x000020d00519636d in AcpiWalkResources(ACPI_HANDLE, char*, ACPI_WALK_RESOURCE_CALLBACK, void*) ../../third_party/acpica/source/components/resources/rsxface.c:731 <platform-bus-x86.so>+0x2d436d
  #9    0x000020d004fadd48 in acpi::AcpiImpl::WalkResources(acpi::AcpiImpl*, ACPI_HANDLE, const char*, acpi::Acpi::ResourcesCallable) ../../src/devices/board/lib/acpi/acpi-impl.cc:41 <platform-bus-x86.so>+0xebd48
  #10   0x000020d004fb394d in acpi::DeviceBuilder::GatherResources(acpi::DeviceBuilder*, acpi::Acpi*, fidl::AnyArena&, acpi::Manager*, acpi::DeviceBuilder::GatherResourcesCallback) ../../src/devices/board/lib/acpi/device-builder.cc:52 <platform-bus-x86.so>+0xf194d
  #11   0x000020d00503faf2 in acpi::Manager::ConfigureDiscoveredDevices(acpi::Manager*) ../../src/devices/board/lib/acpi/manager.cc:75 <platform-bus-x86.so>+0x17daf2
  #12   0x000020d004f67b44 in publish_acpi_devices(acpi::Manager*, zx_device_t*, zx_device_t*) ../../src/devices/board/drivers/x86/acpi-nswalk.cc:102 <platform-bus-x86.so>+0xa5b44
  #13   0x000020d004f796f7 in x86::X86::DoInit(x86::X86*) ../../src/devices/board/drivers/x86/x86.cc:65 <platform-bus-x86.so>+0xb76f7
  #14.1 0x000020d004f838ea in λ(x86::X86::DdkInit::(anon class)*) ../../src/devices/board/drivers/x86/x86.cc:82 <platform-bus-x86.so>+0xc18ea
  #14   0x000020d004f838ea in fit::internal::target<(lambda at../../src/devices/board/drivers/x86/x86.cc:81:19), false, false, void>::invoke(void*) ../../sdk/lib/fit/include/lib/fit/internal/function.h:181 <platform-bus-x86.so>+0xc18ea
  #15.2 0x000020d0051c896c in fit::internal::function_base<16UL, false, void()>::invoke(const fit::internal::function_base<16UL, false, void ()>*) ../../sdk/lib/fit/include/lib/fit/internal/function.h:505 <platform-bus-x86.so>+0x30696c
  #15.1 0x000020d0051c896c in fit::function_impl<16UL, false, void()>::operator()(const fit::function_impl<16UL, false, void ()>*) ../../sdk/lib/fit/include/lib/fit/function.h:300 <platform-bus-x86.so>+0x30696c
  #15   0x000020d0051c896c in async::internal::RetainedTask::Handler(async_dispatcher_t*, async_task_t*, zx_status_t) ../../zircon/system/ulib/async/task.cc:25 <platform-bus-x86.so>+0x30696c
  #16.1 0x00002061a33d3d91 in λ(const driver_runtime::Dispatcher::PostTask::(anon class)*, std::__2::unique_ptr<driver_runtime::CallbackRequest, std::__2::default_delete<driver_runtime::CallbackRequest> >, zx_status_t) ../../src/devices/bin/driver_runtime/dispatcher.cc:715 <libdriver_runtime.so>+0x4bd91
  #16   0x00002061a33d3d91 in fit::internal::target<(lambda at../../src/devices/bin/driver_runtime/dispatcher.cc:714:7), true, false, void, std::__2::unique_ptr<driver_runtime::CallbackRequest, std::__2::default_delete<driver_runtime::CallbackRequest>>, int>::invoke(void*, std::__2::unique_ptr<driver_runtime::CallbackRequest, std::__2::default_delete<driver_runtime::CallbackRequest> >, int) ../../sdk/lib/fit/include/lib/fit/internal/function.h:128 <libdriver_runtime.so>+0x4bd91
  #17   0x00002061a33ccbc9 in fit::internal::function_base<24UL, true, void(std::__2::unique_ptr<driver_runtime::CallbackRequest, std::__2::default_delete<driver_runtime::CallbackRequest>>, int)>::invoke(const fit::internal::function_base<24UL, true, void (std::__2::unique_ptr<driver_runtime::CallbackRequest, std::__2::default_delete<driver_runtime::CallbackRequest> >, int)>*, std::__2::unique_ptr<driver_runtime::CallbackRequest, std::__2::default_delete<driver_runtime::CallbackRequest> >, int) ../../sdk/lib/fit/include/lib/fit/internal/function.h:505 <libdriver_runtime.so>+0x44bc9
  #18   0x00002061a33cc8dd in fit::callback_impl<24UL, true, void(std::__2::unique_ptr<driver_runtime::CallbackRequest, std::__2::default_delete<driver_runtime::CallbackRequest>>, int)>::operator()(fit::callback_impl<24UL, true, void (std::__2::unique_ptr<driver_runtime::CallbackRequest, std::__2::default_delete<driver_runtime::CallbackRequest> >, int)>*, std::__2::unique_ptr<driver_runtime::CallbackRequest, std::__2::default_delete<driver_runtime::CallbackRequest> >, int) ../../sdk/lib/fit/include/lib/fit/function.h:451 <libdriver_runtime.so>+0x448dd
  #19   0x00002061a33bd6a6 in driver_runtime::CallbackRequest::Call(driver_runtime::CallbackRequest*, std::__2::unique_ptr<driver_runtime::CallbackRequest, std::__2::default_delete<driver_runtime::CallbackRequest> >, zx_status_t) ../../src/devices/bin/driver_runtime/callback_request.h:67 <libdriver_runtime.so>+0x356a6
  #20   0x00002061a33c44c8 in driver_runtime::Dispatcher::DispatchCallback(driver_runtime::Dispatcher*, std::__2::unique_ptr<driver_runtime::CallbackRequest, std::__2::default_delete<driver_runtime::CallbackRequest> >) ../../src/devices/bin/driver_runtime/dispatcher.cc:1093 <libdriver_runtime.so>+0x3c4c8
  #21   0x00002061a33c52c1 in driver_runtime::Dispatcher::DispatchCallbacks(driver_runtime::Dispatcher*, std::__2::unique_ptr<driver_runtime::Dispatcher::EventWaiter, std::__2::default_delete<driver_runtime::Dispatcher::EventWaiter> >, fbl::RefPtr<driver_runtime::Dispatcher>) ../../src/devices/bin/driver_runtime/dispatcher.cc:1169 <libdriver_runtime.so>+0x3d2c1
  #22.1 0x00002061a33d081e in λ(std::__2::unique_ptr<driver_runtime::Dispatcher::EventWaiter, std::__2::default_delete<driver_runtime::Dispatcher::EventWaiter> >, fbl::RefPtr<driver_runtime::Dispatcher>, const driver_runtime::Dispatcher::CreateWithAdder::(anon class)*) ../../src/devices/bin/driver_runtime/dispatcher.cc:338 <libdriver_runtime.so>+0x4881e
  #22   0x00002061a33d081e in fit::internal::target<(lambda at../../src/devices/bin/driver_runtime/dispatcher.cc:337:7), true, false, void, std::__2::unique_ptr<driver_runtime::Dispatcher::EventWaiter, std::__2::default_delete<driver_runtime::Dispatcher::EventWaiter>>, fbl::RefPtr<driver_runtime::Dispatcher>>::invoke(void*, std::__2::unique_ptr<driver_runtime::Dispatcher::EventWaiter, std::__2::default_delete<driver_runtime::Dispatcher::EventWaiter> >, fbl::RefPtr<driver_runtime::Dispatcher>) ../../sdk/lib/fit/include/lib/fit/internal/function.h:128 <libdriver_runtime.so>+0x4881e
  #23   0x00002061a33cce7e in fit::internal::function_base<8UL, true, void(std::__2::unique_ptr<driver_runtime::Dispatcher::EventWaiter, std::__2::default_delete<driver_runtime::Dispatcher::EventWaiter>>, fbl::RefPtr<driver_runtime::Dispatcher>)>::invoke(const fit::internal::function_base<8UL, true, void (std::__2::unique_ptr<driver_runtime::Dispatcher::EventWaiter, std::__2::default_delete<driver_runtime::Dispatcher::EventWaiter> >, fbl::RefPtr<driver_runtime::Dispatcher>)>*, std::__2::unique_ptr<driver_runtime::Dispatcher::EventWaiter, std::__2::default_delete<driver_runtime::Dispatcher::EventWaiter> >, fbl::RefPtr<driver_runtime::Dispatcher>) ../../sdk/lib/fit/include/lib/fit/internal/function.h:505 <libdriver_runtime.so>+0x44e7e
  #24.1 0x00002061a33c6964 in fit::function_impl<8UL, true, void(std::__2::unique_ptr<driver_runtime::Dispatcher::EventWaiter, std::__2::default_delete<driver_runtime::Dispatcher::EventWaiter>>, fbl::RefPtr<driver_runtime::Dispatcher>)>::operator()(const fit::function_impl<8UL, true, void (std::__2::unique_ptr<driver_runtime::Dispatcher::EventWaiter, std::__2::default_delete<driver_runtime::Dispatcher::EventWaiter> >, fbl::RefPtr<driver_runtime::Dispatcher>)>*, std::__2::unique_ptr<driver_runtime::Dispatcher::EventWaiter, std::__2::default_delete<driver_runtime::Dispatcher::EventWaiter> >, fbl::RefPtr<driver_runtime::Dispatcher>) ../../sdk/lib/fit/include/lib/fit/function.h:300 <libdriver_runtime.so>+0x3e964
  #24   0x00002061a33c6964 in driver_runtime::Dispatcher::EventWaiter::InvokeCallback(driver_runtime::Dispatcher::EventWaiter*, std::__2::unique_ptr<driver_runtime::Dispatcher::EventWaiter, std::__2::default_delete<driver_runtime::Dispatcher::EventWaiter> >, fbl::RefPtr<driver_runtime::Dispatcher>) ../../src/devices/bin/driver_runtime/dispatcher.h:299 <libdriver_runtime.so>+0x3e964
  #25   0x00002061a33c635d in driver_runtime::Dispatcher::EventWaiter::HandleEvent(std::__2::unique_ptr<driver_runtime::Dispatcher::EventWaiter, std::__2::default_delete<driver_runtime::Dispatcher::EventWaiter> >, async_dispatcher_t*, async::WaitBase*, zx_status_t, zx_packet_signal_t const*) ../../src/devices/bin/driver_runtime/dispatcher.cc:1259 <libdriver_runtime.so>+0x3e35d
  #26.1 0x00002061a33d0c00 in AsyncLoopOwnedEventHandler<driver_runtime::Dispatcher::EventWaiter>::HandleEvent(AsyncLoopOwnedEventHandler<driver_runtime::Dispatcher::EventWaiter>*, zx_status_t, zx_packet_signal_t const*, async_dispatcher_t*, async::WaitBase*) ../../src/devices/bin/driver_runtime/async_loop_owned_event_handler.h:59 <libdriver_runtime.so>+0x48c00
  #26   0x00002061a33d0c00 in async::WaitMethod<AsyncLoopOwnedEventHandler<driver_runtime::Dispatcher::EventWaiter>, &AsyncLoopOwnedEventHandler<driver_runtime::Dispatcher::EventWaiter>::HandleEvent>::CallHandler(async_dispatcher_t*, async_wait_t*, zx_status_t, zx_packet_signal_t const*) ../../zircon/system/ulib/async/include/lib/async/cpp/wait.h:201 <libdriver_runtime.so>+0x48c00
  #27.1 0x00002061a33f2ead in async_loop_run_once(async_loop_t*, zx_time_t) ../../zircon/system/ulib/async-loop/loop.c:415 <libdriver_runtime.so>+0x6aead
  #27   0x00002061a33f2ead in async_loop_run(async_loop_t*, zx_time_t, _Bool) ../../zircon/system/ulib/async-loop/loop.c:288 <libdriver_runtime.so>+0x6aead
  #28   0x00002061a33f478f in async_loop_run_thread(void*) ../../zircon/system/ulib/async-loop/loop.c:840 <libdriver_runtime.so>+0x6c78f
  #29   0x00004262135b7edc in start_c11(void*) ../../zircon/third_party/ulib/musl/pthread/pthread_create.c:55 <libc.so>+0xd7edc
  #30   0x00004262136e896d in thread_trampoline(uintptr_t, uintptr_t) ../../zircon/system/ulib/runtime/thread.cc:100 <libc.so>+0x20896d

1 files changed, 7 insertions, 2 deletions

diff --git a/source/components/resources/rslist.c b/source/components/resources/rslist.c
index bce499170..cb408197e 100644
--- a/source/components/resources/rslist.c
+++ b/source/components/resources/rslist.c
@@ -209,7 +209,12 @@ AcpiRsConvertAmlToResources (
     if (AcpiUtGetResourceType (Aml) ==
         ACPI_RESOURCE_NAME_SERIAL_BUS)
     {
-        if (AmlResource->CommonSerialBus.Type >
+        /* Avoid undefined behavior: member access within misaligned address */
+
+        AML_RESOURCE_COMMON_SERIALBUS CommonSerialBus;
+        memcpy(&CommonSerialBus, AmlResource, sizeof(CommonSerialBus));
+
+        if (CommonSerialBus.Type >
             AML_RESOURCE_MAX_SERIALBUSTYPE)
         {
             ConversionTable = NULL;
@@ -219,7 +224,7 @@ AcpiRsConvertAmlToResources (
             /* This is an I2C, SPI, UART, or CSI2 SerialBus descriptor */
 
             ConversionTable = AcpiGbl_ConvertResourceSerialBusDispatch [
-                AmlResource->CommonSerialBus.Type];
+                CommonSerialBus.Type];
         }
     }
     else