From 84022cff50511e28bf96a407979ff7ea809b532c Mon Sep 17 00:00:00 2001 From: Douglas Anderson Date: Mon, 22 Jan 2024 16:49:34 -0800 Subject: 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: Douglas Anderson Link: https://lore.kernel.org/r/20240122164935.1.I345e485f36babad76370c59659a706723750d950@changeid Signed-off-by: Kees Cook --- drivers/misc/lkdtm/core.c | 22 ++++++++++++++-------- 1 file changed, 14 insertions(+), 8 deletions(-) (limited to 'drivers/misc') diff --git a/drivers/misc/lkdtm/core.c b/drivers/misc/lkdtm/core.c index 0772e4a4757e..5732fd59a227 100644 --- a/drivers/misc/lkdtm/core.c +++ b/drivers/misc/lkdtm/core.c @@ -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; } -- cgit v1.2.3