x86/kprobes: Prohibit probing on IRQ handlers directly

x86/kprobes: Prohibit probing on IRQ handlers directly

Prohibit probing on IRQ handlers in irqentry_text because
if it interrupts user mode, at that point we haven't changed
to kernel space yet and which eventually leads a double fault.
E.g.

 # echo p apic_timer_interrupt > kprobe_events
 # echo 1 > events/kprobes/enable
 PANIC: double fault, error_code: 0x0
 CPU: 1 PID: 814 Comm: less Not tainted 4.20.0-rc3+ #30
 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996)
 RIP: 0010:error_entry+0x12/0xf0
 [snip]
 Call Trace:
  <ENTRY_TRAMPOLINE>
  ? native_iret+0x7/0x7
  ? async_page_fault+0x8/0x30
  ? trace_hardirqs_on_thunk+0x1c/0x1c
  ? error_entry+0x7c/0xf0
  ? async_page_fault+0x8/0x30
  ? native_iret+0x7/0x7
  ? int3+0xa/0x20
  ? trace_hardirqs_on_thunk+0x1c/0x1c
  ? error_entry+0x7c/0xf0
  ? int3+0xa/0x20
  ? apic_timer_interrupt+0x1/0x20
  </ENTRY_TRAMPOLINE>
 Kernel panic - not syncing: Machine halted.
 Kernel Offset: disabled
 ---[ end Kernel panic - not syncing: Machine halted. ]---

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andrea Righi <righi.andrea@gmail.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/154998796400.31052.8406236614820687840.stgit@devbox
Signed-off-by: Ingo Molnar <mingo@kernel.org>