[lib][uefi] implement missing protocols required by GBL

lib/uefi/blockio_protocols.cpp

@@ -103,21 +103,38 @@ __WEAK EfiStatus open_block_device(EfiHandle handle, const void** intf) {
   return EFI_STATUS_SUCCESS;
 }
 
-EfiStatus list_block_devices(size_t *num_handles, EfiHandle **buf) {
+EfiStatus list_block_devices(size_t *num_handles, EfiHandle *buf) {
+  if (num_handles == nullptr) {
+    return EFI_STATUS_INVALID_PARAMETER;
+  }
+
   size_t device_count = 0;
   bio_iter_devices([&device_count](bdev_t *dev) {
     device_count++;
     return true;
   });
-  auto devices =
-      reinterpret_cast<EfiHandle *>(uefi_malloc(sizeof(EfiHandle) * device_count));
+
+  if (device_count == 0) {
+    *num_handles = 0;
+    return EFI_STATUS_NOT_FOUND;
+  }
+
+  if (*num_handles < device_count) {
+    *num_handles = device_count;
+    return EFI_STATUS_BUFFER_TOO_SMALL;
+  }
+
+  // Allow null buffers for size queries, but require storage before writing.
+  if (buf == nullptr) {
+    return EFI_STATUS_INVALID_PARAMETER;
+  }
+
   size_t i = 0;
-  bio_iter_devices([&i, devices, device_count](bdev_t *dev) {
-    devices[i] = dev->name;
+  bio_iter_devices([&i, buf, device_count](bdev_t *dev) {
+    buf[i] = dev->name;
     i++;
     return i < device_count;
   });
   *num_handles = i;
-  *buf = devices;
   return EFI_STATUS_SUCCESS;
 }

lib/uefi/blockio_protocols.h

@@ -5,6 +5,6 @@
 
 EfiStatus open_block_device(EfiHandle handle, const void **intf);
 
-EfiStatus list_block_devices(size_t *num_handles, EfiHandle **buf);
+EfiStatus list_block_devices(size_t *num_handles, EfiHandle *buf);
 
 #endif