gcc-plugins/stackleak: Use noinstr in favor of notrace

While the stackleak plugin was already using notrace, objtool is now a
bit more picky.  Update the notrace uses to noinstr.  Silences the
following objtool warnings when building with:

CONFIG_DEBUG_ENTRY=y
CONFIG_STACK_VALIDATION=y
CONFIG_VMLINUX_VALIDATION=y
CONFIG_GCC_PLUGIN_STACKLEAK=y

  vmlinux.o: warning: objtool: do_syscall_64()+0x9: call to stackleak_track_stack() leaves .noinstr.text section
  vmlinux.o: warning: objtool: do_int80_syscall_32()+0x9: call to stackleak_track_stack() leaves .noinstr.text section
  vmlinux.o: warning: objtool: exc_general_protection()+0x22: call to stackleak_track_stack() leaves .noinstr.text section
  vmlinux.o: warning: objtool: fixup_bad_iret()+0x20: call to stackleak_track_stack() leaves .noinstr.text section
  vmlinux.o: warning: objtool: do_machine_check()+0x27: call to stackleak_track_stack() leaves .noinstr.text section
  vmlinux.o: warning: objtool: .text+0x5346e: call to stackleak_erase() leaves .noinstr.text section
  vmlinux.o: warning: objtool: .entry.text+0x143: call to stackleak_erase() leaves .noinstr.text section
  vmlinux.o: warning: objtool: .entry.text+0x10eb: call to stackleak_erase() leaves .noinstr.text section
  vmlinux.o: warning: objtool: .entry.text+0x17f9: call to stackleak_erase() leaves .noinstr.text section

Note that the plugin's addition of calls to stackleak_track_stack() from
noinstr functions is expected to be safe, as it isn't runtime
instrumentation and is self-contained.

Cc: Alexander Popov <alex.popov@linux.com>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/stackleak.c

@@ -70,7 +70,7 @@ late_initcall(stackleak_sysctls_init);
 #define skip_erasing()	false
 #endif /* CONFIG_STACKLEAK_RUNTIME_DISABLE */
 
-asmlinkage void notrace stackleak_erase(void)
+asmlinkage void noinstr stackleak_erase(void)
 {
 	/* It would be nice not to have 'kstack_ptr' and 'boundary' on stack */
 	unsigned long kstack_ptr = current->lowest_stack;
@@ -124,9 +124,8 @@ asmlinkage void notrace 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 __no_caller_saved_registers notrace stackleak_track_stack(void)
+void __used __no_caller_saved_registers noinstr stackleak_track_stack(void)
 {
 	unsigned long sp = current_stack_pointer;