arm64: entry: use stackleak_erase_on_task_stack()

On arm64 we always call stackleak_erase() on a task stack, and never
call it on another stack. We can avoid some redundant work by using
stackleak_erase_on_task_stack(), telling the stackleak code that it's
being called on a task stack.

Signed-off-by: Mark Rutland <[e-mail]>
Cc: Alexander Popov <[e-mail]>
Cc: Andrew Morton <[e-mail]>
Cc: Andy Lutomirski <[e-mail]>
Cc: Catalin Marinas <[e-mail]>
Cc: Kees Cook <[e-mail]>
Cc: Will Deacon <[e-mail]>
Acked-by: Catalin Marinas <[e-mail]>
Signed-off-by: Kees Cook <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

arch/arm64/kernel/entry.S

···
 	ldr	x19, [tsk, #TSK_TI_FLAGS]	// re-check for single-step
 	enable_step_tsk x19, x2
 #ifdef CONFIG_GCC_PLUGIN_STACKLEAK
-	bl	stackleak_erase
+	bl	stackleak_erase_on_task_stack
 #endif
 	kernel_exit 0
 SYM_CODE_END(ret_to_user)