ACPICA: Fix race in generic_serial_bus (I2C) and GPIO op_region parameter handling

ACPICA commit c9e0116952363b0fa815143dca7e9a2eb4fefa61

The handling of the generic_serial_bus (I2C) and GPIO op_regions in
acpi_ev_address_space_dispatch() passes a number of extra parameters
to the address-space handler through the address-space Context pointer
(instead of using more function parameters).

The Context is shared between threads, so if multiple threads try to
call the handler for the same address-space at the same time, then
a second thread could change the parameters of a first thread while
the handler is running for the first thread.

An example of this race hitting is the Lenovo Yoga Tablet2 1015L,
where there are both attrib_bytes accesses and attrib_byte accesses
to the same address-space. The attrib_bytes access stores the number
of bytes to transfer in Context->access_length. Where as for the
attrib_byte access the number of bytes to transfer is always 1 and
field_obj->Field.access_length is unused (so 0). Both types of
accesses racing from different threads leads to the following problem:

 1. Thread a. starts an attrib_bytes access, stores a non 0 value
    from field_obj->Field.access_length in Context->access_length

 2. Thread b. starts an attrib_byte access, stores 0 in
    Context->access_length

 3. Thread a. calls i2c_acpi_space_handler() (under Linux). Which
    sees that the access-type is ACPI_GSB_ACCESS_ATTRIB_MULTIBYTE
    and calls acpi_gsb_i2c_read_bytes(..., Context->access_length)

 4. At this point Context->access_length is 0 (set by thread b.)

rather then the field_obj->Field.access_length value from thread a.
This 0 length reads leads to the following errors being logged:

 i2c i2c-0: adapter quirk: no zero length (addr 0x0078, size 0, read)
 i2c i2c-0: i2c read 0 bytes from client@0x78 starting at reg 0x0 failed, error: -95

Note this is just an example of the problems which this race can cause.

There are likely many more (sporadic) problems caused by this race.

This commit adds a new context_mutex to struct acpi_object_addr_handler
and makes acpi_ev_address_space_dispatch() take that mutex when
using the shared Context to pass extra parameters to an address-space
handler, fixing this race.

Note the new mutex must be taken *after* exiting the interpreter,
therefor the existing acpi_ex_exit_interpreter() call is moved to above
the code which stores the extra parameters in the Context.

Link: https://github.com/acpica/acpica/commit/c9e01169
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Erik Kaneda <erik.kaneda@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/acpica/acobject.h

@@ -284,6 +284,7 @@ struct acpi_object_addr_handler {
 	acpi_adr_space_handler handler;
 	struct acpi_namespace_node *node;	/* Parent device */
 	void *context;
+	acpi_mutex context_mutex;
 	acpi_adr_space_setup setup;
 	union acpi_operand_object *region_list;	/* Regions using this handler */
 	union acpi_operand_object *next;

drivers/acpi/acpica/evhandler.c

@@ -489,6 +489,13 @@ acpi_ev_install_space_handler(struct acpi_namespace_node *node,
 
 	/* Init handler obj */
 
+	status =
+	    acpi_os_create_mutex(&handler_obj->address_space.context_mutex);
+	if (ACPI_FAILURE(status)) {
+		acpi_ut_remove_reference(handler_obj);
+		goto unlock_and_exit;
+	}
+
 	handler_obj->address_space.space_id = (u8)space_id;
 	handler_obj->address_space.handler_flags = flags;
 	handler_obj->address_space.region_list = NULL;

drivers/acpi/acpica/evregion.c

@@ -112,6 +112,8 @@ acpi_ev_address_space_dispatch(union acpi_operand_object *region_obj,
 	union acpi_operand_object *region_obj2;
 	void *region_context = NULL;
 	struct acpi_connection_info *context;
+	acpi_mutex context_mutex;
+	u8 context_locked;
 	acpi_physical_address address;
 
 	ACPI_FUNCTION_TRACE(ev_address_space_dispatch);
@@ -136,6 +138,8 @@ acpi_ev_address_space_dispatch(union acpi_operand_object *region_obj,
 	}
 
 	context = handler_desc->address_space.context;
+	context_mutex = handler_desc->address_space.context_mutex;
+	context_locked = FALSE;
 
 	/*
 	 * It may be the case that the region has never been initialized.
@@ -204,41 +208,6 @@ acpi_ev_address_space_dispatch(union acpi_operand_object *region_obj,
 	handler = handler_desc->address_space.handler;
 	address = (region_obj->region.address + region_offset);
 
-	/*
-	 * Special handling for generic_serial_bus and general_purpose_io:
-	 * There are three extra parameters that must be passed to the
-	 * handler via the context:
-	 *   1) Connection buffer, a resource template from Connection() op
-	 *   2) Length of the above buffer
-	 *   3) Actual access length from the access_as() op
-	 *
-	 * In addition, for general_purpose_io, the Address and bit_width fields
-	 * are defined as follows:
-	 *   1) Address is the pin number index of the field (bit offset from
-	 *      the previous Connection)
-	 *   2) bit_width is the actual bit length of the field (number of pins)
-	 */
-	if ((region_obj->region.space_id == ACPI_ADR_SPACE_GSBUS) &&
-	    context && field_obj) {
-
-		/* Get the Connection (resource_template) buffer */
-
-		context->connection = field_obj->field.resource_buffer;
-		context->length = field_obj->field.resource_length;
-		context->access_length = field_obj->field.access_length;
-	}
-	if ((region_obj->region.space_id == ACPI_ADR_SPACE_GPIO) &&
-	    context && field_obj) {
-
-		/* Get the Connection (resource_template) buffer */
-
-		context->connection = field_obj->field.resource_buffer;
-		context->length = field_obj->field.resource_length;
-		context->access_length = field_obj->field.access_length;
-		address = field_obj->field.pin_number_index;
-		bit_width = field_obj->field.bit_length;
-	}
-
 	ACPI_DEBUG_PRINT((ACPI_DB_OPREGION,
 			  "Handler %p (@%p) Address %8.8X%8.8X [%s]\n",
 			  &region_obj->region.handler->address_space, handler,
@@ -256,11 +225,71 @@ acpi_ev_address_space_dispatch(union acpi_operand_object *region_obj,
 		acpi_ex_exit_interpreter();
 	}
 
+	/*
+	 * Special handling for generic_serial_bus and general_purpose_io:
+	 * There are three extra parameters that must be passed to the
+	 * handler via the context:
+	 *   1) Connection buffer, a resource template from Connection() op
+	 *   2) Length of the above buffer
+	 *   3) Actual access length from the access_as() op
+	 *
+	 * Since we pass these extra parameters via the context, which is
+	 * shared between threads, we must lock the context to avoid these
+	 * parameters being changed from another thread before the handler
+	 * has completed running.
+	 *
+	 * In addition, for general_purpose_io, the Address and bit_width fields
+	 * are defined as follows:
+	 *   1) Address is the pin number index of the field (bit offset from
+	 *      the previous Connection)
+	 *   2) bit_width is the actual bit length of the field (number of pins)
+	 */
+	if ((region_obj->region.space_id == ACPI_ADR_SPACE_GSBUS) &&
+	    context && field_obj) {
+
+		status =
+		    acpi_os_acquire_mutex(context_mutex, ACPI_WAIT_FOREVER);
+		if (ACPI_FAILURE(status)) {
+			goto re_enter_interpreter;
+		}
+
+		context_locked = TRUE;
+
+		/* Get the Connection (resource_template) buffer */
+
+		context->connection = field_obj->field.resource_buffer;
+		context->length = field_obj->field.resource_length;
+		context->access_length = field_obj->field.access_length;
+	}
+	if ((region_obj->region.space_id == ACPI_ADR_SPACE_GPIO) &&
+	    context && field_obj) {
+
+		status =
+		    acpi_os_acquire_mutex(context_mutex, ACPI_WAIT_FOREVER);
+		if (ACPI_FAILURE(status)) {
+			goto re_enter_interpreter;
+		}
+
+		context_locked = TRUE;
+
+		/* Get the Connection (resource_template) buffer */
+
+		context->connection = field_obj->field.resource_buffer;
+		context->length = field_obj->field.resource_length;
+		context->access_length = field_obj->field.access_length;
+		address = field_obj->field.pin_number_index;
+		bit_width = field_obj->field.bit_length;
+	}
+
 	/* Call the handler */
 
 	status = handler(function, address, bit_width, value, context,
 			 region_obj2->extra.region_context);
 
+	if (context_locked) {
+		acpi_os_release_mutex(context_mutex);
+	}
+
 	if (ACPI_FAILURE(status)) {
 		ACPI_EXCEPTION((AE_INFO, status, "Returned by Handler for [%s]",
 				acpi_ut_get_region_name(region_obj->region.
@@ -277,6 +306,7 @@ acpi_ev_address_space_dispatch(union acpi_operand_object *region_obj,
 		}
 	}
 
+re_enter_interpreter:
 	if (!(handler_desc->address_space.handler_flags &
 	      ACPI_ADDR_HANDLER_DEFAULT_INSTALLED)) {
 		/*

drivers/acpi/acpica/evxfregn.c

@@ -201,6 +201,8 @@ acpi_remove_address_space_handler(acpi_handle device,
 
 			/* Now we can delete the handler object */
 
+			acpi_os_release_mutex(handler_obj->address_space.
+					      context_mutex);
 			acpi_ut_remove_reference(handler_obj);
 			goto unlock_and_exit;
 		}