Commit 84022cff authored by Douglas Anderson's avatar Douglas Anderson Committed by Kees Cook
Browse files

lkdtm: Make lkdtm_do_action() return to avoid tail call optimization 



The comments for lkdtm_do_action() explicitly call out that it
shouldn't be inlined because we want it to show up in stack
crawls. However, at least with some compilers / options it's still
vanishing due to tail call optimization. Let's add a return value to
the function to make it harder for the compiler to do tail call
optimization here.

Now that we have a return value, we can actually use it in the
callers, which is a minor improvement in the code.

Signed-off-by: default avatarDouglas Anderson <dianders@chromium.org>
Link: https://lore.kernel.org/r/20240122164935.1.I345e485f36babad76370c59659a706723750d950@changeid


Signed-off-by: default avatarKees Cook <keescook@chromium.org>
parent 41bccc98

drivers/misc/lkdtm/core.c

+14 −8
Original line number Diff line number Diff line
@@ -153,12 +153,17 @@ static const struct crashtype *find_crashtype(const char *name) 
/*

 * This is forced noinline just so it distinctly shows up in the stackdump

 * which makes validation of expected lkdtm crashes easier.

 *

 * NOTE: having a valid return value helps prevent the compiler from doing

 * tail call optimizations and taking this out of the stack trace.

 */

static noinline void lkdtm_do_action(const struct crashtype *crashtype)

static noinline int lkdtm_do_action(const struct crashtype *crashtype)

{

	if (WARN_ON(!crashtype || !crashtype->func))

		return;

		return -EINVAL;

	crashtype->func();



	return 0;

}



static int lkdtm_register_cpoint(struct crashpoint *crashpoint,
@@ -167,10 +172,8 @@ static int lkdtm_register_cpoint(struct crashpoint *crashpoint, 
	int ret;



	/* If this doesn't have a symbol, just call immediately. */

	if (!crashpoint->kprobe.symbol_name) {

		lkdtm_do_action(crashtype);

		return 0;

	}

	if (!crashpoint->kprobe.symbol_name)

		return lkdtm_do_action(crashtype);



	if (lkdtm_kprobe != NULL)

		unregister_kprobe(lkdtm_kprobe);
@@ -216,7 +219,7 @@ static int lkdtm_kprobe_handler(struct kprobe *kp, struct pt_regs *regs) 
	spin_unlock_irqrestore(&crash_count_lock, flags);



	if (do_it)

		lkdtm_do_action(lkdtm_crashtype);

		return lkdtm_do_action(lkdtm_crashtype);



	return 0;

}
@@ -303,6 +306,7 @@ static ssize_t direct_entry(struct file *f, const char __user *user_buf, 
{

	const struct crashtype *crashtype;

	char *buf;

	int err;



	if (count >= PAGE_SIZE)

		return -EINVAL;
@@ -326,9 +330,11 @@ static ssize_t direct_entry(struct file *f, const char __user *user_buf, 
		return -EINVAL;



	pr_info("Performing direct entry %s\n", crashtype->name);

	lkdtm_do_action(crashtype);

	err = lkdtm_do_action(crashtype);

	*off += count;



	if (err)

		return err;

	return count;

}