ACPICA: Add a mechanism to escape infinite AML While() loops

Add a loop counter to force exit from AML While loops if the
count becomes too large. This can occur in poorly written AML
when the hardware does not respond within a while loop and the
loop does not implement a timeout. The maximum loop count is
configurable. A new exception code is returned when a loop is
broken, AE_AML_INFINITE_LOOP.  Bob Moore, Alexey Starikovskiy.

Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Lin Ming <ming.m.lin@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>

1 files changed, 21 insertions, 3 deletions

diff --git a/drivers/acpi/dispatcher/dsopcode.c b/drivers/acpi/dispatcher/dsopcode.c
index 5cd406676c2c..50c892a49fa3 100644
--- a/drivers/acpi/dispatcher/dsopcode.c
+++ b/drivers/acpi/dispatcher/dsopcode.c
@@ -1262,13 +1262,31 @@ acpi_ds_exec_end_control_op(struct acpi_walk_state * walk_state,
 
                 ACPI_DEBUG_PRINT((ACPI_DB_DISPATCH, "[WHILE_OP] Op=%p\n", op));
 
-                if (walk_state->control_state->common.value) {
+                control_state = walk_state->control_state;
+                if (control_state->common.value) {
 
-                        /* Predicate was true, go back and evaluate it again! */
+                        /* Predicate was true, the body of the loop was just executed */
 
+                        /*
+                         * This loop counter mechanism allows the interpreter to escape
+                         * possibly infinite loops. This can occur in poorly written AML
+                         * when the hardware does not respond within a while loop and the
+                         * loop does not implement a timeout.
+                         */
+                        control_state->control.loop_count++;
+                        if (control_state->control.loop_count >
+                                ACPI_MAX_LOOP_ITERATIONS) {
+                                status = AE_AML_INFINITE_LOOP;
+                                break;
+                        }
+
+                        /*
+                         * Go back and evaluate the predicate and maybe execute the loop
+                         * another time
+                         */
                         status = AE_CTRL_PENDING;
                         walk_state->aml_last_while =
-                            walk_state->control_state->control.aml_predicate_start;
+                            control_state->control.aml_predicate_start;
                         break;
                 }