ARM: 9064/1: hw_breakpoint: Do not directly check the event's overflow_handler hook

In the Linux kernel, the following vulnerability has been resolved:

ARM: 9064/1: hw_breakpoint: Do not directly check the event's overflow_handler hook

The commit 1879445dfa7b ("perf/core: Set event's default

::overflow_handler()") set a default event->overflow_handler in

perf_event_alloc(), and replace the check event->overflow_handler with

is_default_overflow_handler(), but one is missing.

Currently, the bp->overflow_handler can not be NULL. As a result,

enable_single_step() is always not invoked.

Comments from Zhen Lei:

https://patchwork.kernel.org/project/linux-arm-kernel/patch/[email protected]/