stackleak: Disable function tracing and kprobes for stackleak_erase()

The stackleak_erase() function is called on the trampoline stack at the
end of syscall. This stack is not big enough for ftrace and kprobes
operations, e.g. it can be exhausted if we use kprobe_events for
stackleak_erase().

So let's disable function tracing and kprobes of stackleak_erase().

Reported-by: kernel test robot <lkp@intel.com>
Fixes: 10e9ae9 ("gcc-plugins: Add STACKLEAK plugin for tracking the kernel stack")
Signed-off-by: Alexander Popov <alex.popov@linux.com>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>

kernel/stackleak.c

@@ -11,6 +11,7 @@
  */
 
 #include <linux/stackleak.h>
+#include <linux/kprobes.h>
 
 #ifdef CONFIG_STACKLEAK_RUNTIME_DISABLE
 #include <linux/jump_label.h>
@@ -47,7 +48,7 @@ int stack_erasing_sysctl(struct ctl_table *table, int write,
 #define skip_erasing()	false
 #endif /* CONFIG_STACKLEAK_RUNTIME_DISABLE */
 
-asmlinkage void stackleak_erase(void)
+asmlinkage void notrace stackleak_erase(void)
 {
 	/* It would be nice not to have 'kstack_ptr' and 'boundary' on stack */
 	unsigned long kstack_ptr = current->lowest_stack;
@@ -101,6 +102,7 @@ asmlinkage void stackleak_erase(void)
 	/* Reset the 'lowest_stack' value for the next syscall */
 	current->lowest_stack = current_top_of_stack() - THREAD_SIZE/64;
 }
+NOKPROBE_SYMBOL(stackleak_erase);
 
 void __used stackleak_track_stack(void)
 {