fix(core): properly cache last successful unlock time

core/src/apps/common/request_pin.py

@@ -1,5 +1,6 @@
 import utime
 
+import storage.cache
 import storage.sd_salt
 from trezor import config, ui, wire
 from trezor.messages import ButtonRequestType
@@ -14,9 +15,6 @@ if False:
     from typing import Any, NoReturn
 
 
-_last_successful_unlock = 0
-
-
 def can_lock_device() -> bool:
     """Return True if the device has a PIN set or SD-protect enabled."""
     return config.has_pin() or storage.sd_salt.is_enabled()
@@ -79,6 +77,19 @@ async def request_pin_and_sd_salt(
     return pin, salt
 
 
+def _set_last_unlock_time() -> None:
+    now = utime.ticks_ms()
+    storage.cache.set(
+        storage.cache.APP_COMMON_REQUEST_PIN_LAST_UNLOCK, now.to_bytes(4, "big")
+    )
+
+
+def _get_last_unlock_time() -> int:
+    return int.from_bytes(
+        storage.cache.get(storage.cache.APP_COMMON_REQUEST_PIN_LAST_UNLOCK), "big"
+    )
+
+
 async def verify_user_pin(
     ctx: wire.GenericContext = wire.DUMMY_CONTEXT,
     prompt: str = "Enter your PIN",
@@ -86,11 +97,11 @@ async def verify_user_pin(
     retry: bool = True,
     cache_time_ms: int = 0,
 ) -> None:
-    global _last_successful_unlock
+    last_unlock = _get_last_unlock_time()
     if (
         cache_time_ms
-        and _last_successful_unlock
-        and utime.ticks_ms() - _last_successful_unlock <= cache_time_ms
+        and last_unlock
+        and utime.ticks_ms() - last_unlock <= cache_time_ms
         and config.is_unlocked()
     ):
         return
@@ -106,7 +117,7 @@ async def verify_user_pin(
     except SdCardUnavailable:
         raise wire.PinCancelled("SD salt is unavailable")
     if config.unlock(pin, salt):
-        _last_successful_unlock = utime.ticks_ms()
+        _set_last_unlock_time()
         return
     elif not config.has_pin():
         raise RuntimeError
@@ -116,7 +127,7 @@ async def verify_user_pin(
             ctx, "Wrong PIN, enter again", config.get_pin_rem(), allow_cancel
         )
         if config.unlock(pin, salt):
-            _last_successful_unlock = utime.ticks_ms()
+            _set_last_unlock_time()
             return
 
     raise wire.PinInvalid

core/src/storage/cache.py

@@ -21,6 +21,7 @@ APP_COMMON_AUTHORIZATION_DATA = 4
 APP_COMMON_SEED_WITHOUT_PASSPHRASE = 0 | _SESSIONLESS_FLAG
 APP_COMMON_SAFETY_CHECKS_TEMPORARY = 1 | _SESSIONLESS_FLAG
 STORAGE_DEVICE_EXPERIMENTAL_FEATURES = 2 | _SESSIONLESS_FLAG
+APP_COMMON_REQUEST_PIN_LAST_UNLOCK = 3 | _SESSIONLESS_FLAG
 
 
 # === Homescreen storage ===
@@ -90,6 +91,7 @@ class SessionlessCache(DataCache):
             64,  # APP_COMMON_SEED_WITHOUT_PASSPHRASE
             1,  # APP_COMMON_SAFETY_CHECKS_TEMPORARY
             1,  # STORAGE_DEVICE_EXPERIMENTAL_FEATURES
+            4,  # APP_COMMON_REQUEST_PIN_LAST_UNLOCK
         )
         super().__init__()