[PATCH 5.12 147/178] powerpc/perf: Fix crash in perf_instruction_pointer() when ppmu is not set

[Greg Kroah-Hartman]

From: Athira Rajeev <atrajeev@xxxxxxxxxxxxxxxxxx>

commit 60b7ed54a41b550d50caf7f2418db4a7e75b5bdc upstream.

On systems without any specific PMU driver support registered, running
perf record causes Oops.

The relevant portion from call trace:

  BUG: Kernel NULL pointer dereference on read at 0x00000040
  Faulting instruction address: 0xc0021f0c
  Oops: Kernel access of bad area, sig: 11 [#1]
  BE PAGE_SIZE=4K PREEMPT CMPCPRO
  SAF3000 DIE NOTIFICATION
  CPU: 0 PID: 442 Comm: null_syscall Not tainted 5.13.0-rc6-s3k-dev-01645-g7649ee3d2957 #5164
  NIP:  c0021f0c LR: c00e8ad8 CTR: c00d8a5c
  NIP perf_instruction_pointer+0x10/0x60
  LR  perf_prepare_sample+0x344/0x674
  Call Trace:
    perf_prepare_sample+0x7c/0x674 (unreliable)
    perf_event_output_forward+0x3c/0x94
    __perf_event_overflow+0x74/0x14c
    perf_swevent_hrtimer+0xf8/0x170
    __hrtimer_run_queues.constprop.0+0x160/0x318
    hrtimer_interrupt+0x148/0x3b0
    timer_interrupt+0xc4/0x22c
    Decrementer_virt+0xb8/0xbc

During perf record session, perf_instruction_pointer() is called to
capture the sample IP. This function in core-book3s accesses
ppmu->flags. If a platform specific PMU driver is not registered, ppmu
is set to NULL and accessing its members results in a crash. Fix this
crash by checking if ppmu is set.

Fixes: 2ca13a4cc56c ("powerpc/perf: Use regs->nip when SIAR is zero")
Cc: stable@xxxxxxxxxxxxxxx # v5.11+
Reported-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
Signed-off-by: Athira Rajeev <atrajeev@xxxxxxxxxxxxxxxxxx>
Tested-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/1623952506-1431-1-git-send-email-atrajeev@xxxxxxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 arch/powerpc/perf/core-book3s.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c
@@ -2242,7 +2242,7 @@ unsigned long perf_instruction_pointer(s
 	bool use_siar = regs_use_siar(regs);
 	unsigned long siar = mfspr(SPRN_SIAR);
 
-	if (ppmu->flags & PPMU_P10_DD1) {
+	if (ppmu && (ppmu->flags & PPMU_P10_DD1)) {
 		if (siar)
 			return siar;
 		else