feat(core): introduce systask id & task count limit

[no changelog]

core/embed/sys/task/inc/sys/systask.h

@@ -17,8 +17,7 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 
-#ifndef TREZORHAL_SYSTASK_H
-#define TREZORHAL_SYSTASK_H
+#pragma once
 
 #include <trezor_types.h>
 
@@ -97,6 +96,12 @@ typedef void (*systask_error_handler_t)(const systask_postmortem_t* pminfo);
 
 #ifdef KERNEL_MODE
 
+// Maximum number of tasks that can be created
+#define SYSTASK_MAX_TASKS 2
+
+// Zero-based task ID (up SYSTASK_MAX_TASKS - 1)
+typedef uint8_t systask_id_t;
+
 // Task context used by the kernel to save the state of each task
 // when switching between them
 typedef struct {
@@ -111,6 +116,8 @@ typedef struct {
   // Set to nonzero, if the task is killed
   uint32_t killed;
 
+  // Task id
+  systask_id_t id;
   // MPU mode the task is running in
   mpu_mode_t mpu_mode;
   // Task post-mortem information
@@ -134,7 +141,7 @@ void systask_yield_to(systask_t* task);
 // Initializes a task with the given stack pointer, stack size
 //
 // The task must be not be running when the function is called
-void systask_init(systask_t* task, uint32_t stack_ptr, uint32_t stack_size,
+bool systask_init(systask_t* task, uint32_t stack_ptr, uint32_t stack_size,
                   void* context);
 
 // Pushes data onto the stack of the task
@@ -154,6 +161,9 @@ void systask_pop_data(systask_t* task, size_t size);
 bool systask_push_call(systask_t* task, void* fn, uint32_t arg1, uint32_t arg2,
                        uint32_t arg3);
 
+// Gets the Id (zero-based index up SYSTASK_MAX_TASKS - 1) of the given task
+systask_id_t systask_id(systask_t* task);
+
 // Terminates the task with the given exit code
 //
 // If the task is not specified (NULL), it's automatically determined:
@@ -181,5 +191,3 @@ void systask_exit_fatal(systask_t* task, const char* message,
                         int line);
 
 #endif  // KERNEL_MODE
-
-#endif  // TREZORHAL_SYSTASK_H

core/embed/sys/task/stm32/applet.c

@@ -56,8 +56,10 @@ bool applet_reset(applet_t* applet, uint32_t cmd, const void* arg,
   applet_clear_memory(applet);
 
   // Reset the applet task (stack pointer, etc.)
-  systask_init(&applet->task, applet->header->stack.start,
-               applet->header->stack.size, applet);
+  if (!systask_init(&applet->task, applet->header->stack.start,
+                    applet->header->stack.size, applet)) {
+    return false;
+  }
 
   // Copy the arguments onto the applet stack
   void* arg_copy = NULL;

core/embed/sys/task/stm32/systask.c

@@ -53,6 +53,8 @@ typedef struct {
   systask_t* active_task;
   // Task to be scheduled next
   systask_t* waiting_task;
+  // Bitmap of used task IDs
+  uint32_t task_id_map;
 } systask_scheduler_t;
 
 // Global task manager state
@@ -61,8 +63,10 @@ static systask_scheduler_t g_systask_scheduler = {
     // to function correctly before the scheduler is initialized.
     .active_task = &g_systask_scheduler.kernel_task,
     .waiting_task = &g_systask_scheduler.kernel_task,
+    .task_id_map = 0x00000001,  // Kernel task is always present
     .kernel_task = {
         .sp_lim = (uint32_t)&_stack_section_start,
+        .id = 0,  // Kernel task ID == 0
     }};
 
 void systask_scheduler_init(systask_error_handler_t error_handler) {
@@ -73,6 +77,7 @@ void systask_scheduler_init(systask_error_handler_t error_handler) {
   scheduler->error_handler = error_handler;
   scheduler->active_task = &scheduler->kernel_task;
   scheduler->waiting_task = scheduler->active_task;
+  scheduler->task_id_map = 0x00000001;  // Kernel task is always present
 
   scheduler->kernel_task.sp_lim = (uint32_t)&_stack_section_start;
 
@@ -117,16 +122,36 @@ void systask_yield_to(systask_t* task) {
   systask_yield();
 }
 
-void systask_init(systask_t* task, uint32_t stack_ptr, uint32_t stack_size,
+static systask_id_t systask_get_unused_id(void) {
+  systask_id_t id = 0;
+  while (++id < SYSTASK_MAX_TASKS) {
+    if ((g_systask_scheduler.task_id_map & (1 << id)) == 0) {
+      break;
+    }
+  }
+  return id;
+}
+
+bool systask_init(systask_t* task, uint32_t stack_ptr, uint32_t stack_size,
                   void* applet) {
+  systask_id_t id = systask_get_unused_id();
+  if (id >= SYSTASK_MAX_TASKS) {
+    return false;
+  }
+
   memset(task, 0, sizeof(systask_t));
   task->sp = stack_ptr + stack_size;
   task->sp_lim = stack_ptr + 256;
   task->exc_return = 0xFFFFFFED;  // Thread mode, use PSP, pop FP context
+  task->id = id;
   task->mpu_mode = MPU_MODE_APP;
   task->applet = applet;
+
+  return true;
 }
 
+systask_id_t systask_id(const systask_t* task) { return task->id; }
+
 uint32_t* systask_push_data(systask_t* task, const void* data, size_t size) {
   if (task->sp < task->sp_lim) {
     // Stack overflow
@@ -211,6 +236,9 @@ static void systask_kill(systask_t* task) {
     // if it returns. Neither is expected to happen.
     reboot_device();
   } else if (task == scheduler->active_task) {
+    // Free task ID
+    scheduler->task_id_map &= ~(1 << task->id);
+
     // Switch to the kernel task
     systask_yield_to(&scheduler->kernel_task);
   }