[PATCH] parisc: Avoid kernel panic triggered by invalid kprobe

[Helge Deller <deller@xxxxxx>]

When running gdb I was able to trigger this kernel panic:

 Kernel Fault: Code=26 (Data memory access rights trap) at addr 0000000000000060
 CPU: 0 PID: 1401 Comm: gdb-crash Not tainted 5.2.0-rc7-64bit+ #1053

      YZrvWESTHLNXBCVMcbcbcbcbOGFRQPDI
 PSW: 00001000000001000000000000001111 Not tainted
 r00-03  000000000804000f 0000000040dee1a0 0000000040c78cf0 00000000b8d50160
 r04-07  0000000040d2b1a0 000000004360a098 00000000bbbe87b8 0000000000000003
 r08-11  00000000fac20a70 00000000fac24160 00000000fac1bbe0 0000000000000000
 r12-15  00000000fabfb79a 00000000fac244a4 0000000000010000 0000000000000001
 r16-19  00000000bbbe87b8 00000000f8f02910 0000000000010034 0000000000000000
 r20-23  00000000fac24630 00000000fac24630 000000006474e552 00000000fac1aa52
 r24-27  0000000000000028 00000000bbbe87b8 00000000bbbe87b8 0000000040d2b1a0
 r28-31  0000000000000000 00000000b8d501c0 00000000b8d501f0 0000000003424000
 sr00-03  0000000000423000 0000000000000000 0000000000000000 0000000000423000
 sr04-07  0000000000000000 0000000000000000 0000000000000000 0000000000000000

 IASQ: 0000000000000000 0000000000000000 IAOQ: 0000000040c78cf0 0000000040c78cf4
  IIR: 539f00c0    ISR: 0000000000000000  IOR: 0000000000000060
  CPU:        0   CR30: 00000000b8d50000 CR31: 00000000d22345e2
  ORIG_R28: 0000000040250798
  IAOQ[0]: parisc_kprobe_ss_handler+0x58/0x170
  IAOQ[1]: parisc_kprobe_ss_handler+0x5c/0x170
  RP(r2): parisc_kprobe_ss_handler+0x58/0x170
 Backtrace:
  [<0000000040206ff8>] handle_interruption+0x178/0xbb8
 Kernel panic - not syncing: Kernel Fault

Avoid this panic by checking the return value of kprobe_running() and
skip kprobe if none is currently active.

Signed-off-by: Helge Deller <deller@xxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # v5.2

diff --git a/arch/parisc/kernel/kprobes.c b/arch/parisc/kernel/kprobes.c
index d58960b33bda..0385a8fd74aa 100644
--- a/arch/parisc/kernel/kprobes.c
+++ b/arch/parisc/kernel/kprobes.c
@@ -133,6 +133,9 @@ int __kprobes parisc_kprobe_ss_handler(struct pt_regs *regs)
 	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 	struct kprobe *p = kprobe_running();

+	if (!p)
+		return 0;
+
 	if (regs->iaoq[0] != (unsigned long)p->ainsn.insn+4)
 		return 0;