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

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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 <dianders@chromium.org>
Link: https://lore.kernel.org/r/20240122164935.1.I345e485f36babad76370c59659a706723750d950@changeid
Signed-off-by: Kees Cook <keescook@chromium.org>
This commit is contained in:
Douglas Anderson 2024-01-22 16:49:34 -08:00 committed by Kees Cook
parent 41bccc98fb
commit 84022cff50
1 changed files with 14 additions and 8 deletions
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22
drivers/misc/lkdtm/core.c
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@ -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;
}