console: add a clear_screen() primitive

Several places in e.g. MokManager and our console library use
ST->ConOut->ClearScreen directly, without checking for the existence of
a console output device.

This patch adds function to our console library to do that correctly,
instead of using the bug-prone ad hoc implementation everywhere.

Signed-off-by: Peter Jones <pjones@redhat.com>

MokManager.c

@@ -1005,7 +1005,7 @@ static EFI_STATUS mok_reset_prompt(BOOLEAN MokX)
 	EFI_STATUS efi_status;
 	CHAR16 *prompt[] = { NULL, NULL };
 
-	ST->ConOut->ClearScreen(ST->ConOut);
+	clear_screen();
 
 	if (MokX)
 		prompt[0] = L"Erase all stored keys in MokListX?";
@@ -1468,7 +1468,7 @@ static EFI_STATUS mok_sb_prompt(void *MokSB, UINTN MokSBSize)
 		return EFI_INVALID_PARAMETER;
 	}
 
-	ST->ConOut->ClearScreen(ST->ConOut);
+	clear_screen();
 
 	message[0] = L"Change Secure Boot state";
 	message[1] = NULL;
@@ -1583,7 +1583,7 @@ static EFI_STATUS mok_db_prompt(void *MokDB, UINTN MokDBSize)
 		return EFI_INVALID_PARAMETER;
 	}
 
-	ST->ConOut->ClearScreen(ST->ConOut);
+	clear_screen();
 
 	message[0] = L"Change DB state";
 	message[1] = NULL;
@@ -1691,7 +1691,7 @@ static EFI_STATUS mok_pw_prompt(void *MokPW, UINTN MokPWSize)
 		return EFI_INVALID_PARAMETER;
 	}
 
-	ST->ConOut->ClearScreen(ST->ConOut);
+	clear_screen();
 
 	SetMem(hash, PASSWORD_CRYPT_SIZE, 0);
 
@@ -2008,7 +2008,7 @@ static BOOLEAN verify_pw(BOOLEAN * protected)
 	if (attributes & EFI_VARIABLE_RUNTIME_ACCESS)
 		return TRUE;
 
-	ST->ConOut->ClearScreen(ST->ConOut);
+	clear_screen();
 
 	/* Draw the background */
 	console_save_and_set_mode(&SavedMode);

include/console.h

@@ -50,6 +50,9 @@ void
 console_reset(void);
 void
 console_mode_handle(void);
+void
+clear_screen(void);
+
 #define NOSEL 0x7fffffff
 
 typedef struct _EFI_CONSOLE_CONTROL_PROTOCOL   EFI_CONSOLE_CONTROL_PROTOCOL;

lib/console.c

@@ -580,7 +580,7 @@ console_mode_handle(VOID)
 		efi_status = co->SetMode(co, mode_set);
 	}
 
-	co->ClearScreen(co);
+	clear_screen();
 
 	if (EFI_ERROR(efi_status)) {
 		console_error(L"Console set mode fail", efi_status);
@@ -683,6 +683,17 @@ console_reset(void)
 	co->ClearScreen(co);
 }
 
+void
+clear_screen(void)
+{
+	SIMPLE_TEXT_OUTPUT_INTERFACE *co = ST->ConOut;
+
+	if (!co)
+		return;
+
+	co->ClearScreen(co);
+}
+
 VOID
 setup_verbosity(VOID)
 {