kprobes: Reduce preempt disable scope in check_kprobe_access_safe()

Commit a189d0350f387 ("kprobes: disable preempt for module_text_address() and kernel_text_address()")
introduced a preempt_disable() region to protect against concurrent
module unloading. However this region also includes the call to
jump_label_text_reserved() which takes a long time;
up to 400us, iterating over approx 6000 jump tables.

The scope protected by preempt_disable() is largen than necessary.
core_kernel_text() does not need to be protected as it does not interact
with module code at all.
Only the scope from __module_text_address() to try_module_get() needs to
be protected.
By limiting the critical section to __module_text_address() and
try_module_get() the function responsible for the latency spike remains
preemptible.

This works fine even when !CONFIG_MODULES as in that case
try_module_get() will always return true and that block can be optimized
away.

Limit the critical section to __module_text_address() and
try_module_get(). Use guard(preempt)() for easier error handling.

While at it also remove a spurious *probed_mod = NULL in an error
path. On errors the output parameter is never inspected by the caller.
Some error paths were clearing the parameters, some didn't.
Align them for clarity.

Link: https://lore.kernel.org/all/20241121-kprobes-preempt-v1-1-fd581ee7fcbb@linutronix.de/

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

0 files changed, 0 insertions, 0 deletions