Commit 8646698a authored by Steven Rostedt (VMware)'s avatar Steven Rostedt (VMware)
Browse files

x86/ftrace: Remove fault protection code in prepare_ftrace_return 

Removing the fault protection code when writing return_hooker
to stack. As Steven noted:

> That protection was there from the beginning due to being "paranoid",
> considering ftrace was bricking network cards. But that protection
> would not have even protected against that.

Link: https://lkml.kernel.org/r/20211008091336.33616-3-jolsa@kernel.org



Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: default avatarJiri Olsa <jolsa@kernel.org>
Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
parent 1e85010e

arch/x86/kernel/ftrace.c

+3 −35
Original line number Diff line number Diff line
@@ -620,12 +620,10 @@ int ftrace_disable_ftrace_graph_caller(void) 
 * Hook the return address and push it in the stack of return addrs

 * in current thread info.

 */

void prepare_ftrace_return(unsigned long self_addr, unsigned long *parent,

void prepare_ftrace_return(unsigned long ip, unsigned long *parent,

			   unsigned long frame_pointer)

{

	unsigned long return_hooker = (unsigned long)&return_to_handler;

	unsigned long old;

	int faulted;



	/*

	 * When resuming from suspend-to-ram, this function can be indirectly
@@ -645,37 +643,7 @@ void prepare_ftrace_return(unsigned long self_addr, unsigned long *parent, 
	if (unlikely(atomic_read(&current->tracing_graph_pause)))

		return;



	/*

	 * Protect against fault, even if it shouldn't

	 * happen. This tool is too much intrusive to

	 * ignore such a protection.

	 */

	asm volatile(

		"1: " _ASM_MOV " (%[parent]), %[old]\n"

		"2: " _ASM_MOV " %[return_hooker], (%[parent])\n"

		"   movl $0, %[faulted]\n"

		"3:\n"



		".section .fixup, \"ax\"\n"

		"4: movl $1, %[faulted]\n"

		"   jmp 3b\n"

		".previous\n"



		_ASM_EXTABLE(1b, 4b)

		_ASM_EXTABLE(2b, 4b)



		: [old] "=&r" (old), [faulted] "=r" (faulted)

		: [parent] "r" (parent), [return_hooker] "r" (return_hooker)

		: "memory"

	);



	if (unlikely(faulted)) {

		ftrace_graph_stop();

		WARN_ON(1);

		return;

	}



	if (function_graph_enter(old, self_addr, frame_pointer, parent))

		*parent = old;

	if (!function_graph_enter(*parent, ip, frame_pointer, parent))

		*parent = return_hooker;

}

#endif /* CONFIG_FUNCTION_GRAPH_TRACER */