This is a note to let you know that I've just added the patch titled powerpc/perf: Fix crash in perf_instruction_pointer() when ppmu is not set to the 5.12-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: powerpc-perf-fix-crash-in-perf_instruction_pointer-when-ppmu-is-not-set.patch and it can be found in the queue-5.12 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 60b7ed54a41b550d50caf7f2418db4a7e75b5bdc Mon Sep 17 00:00:00 2001 From: Athira Rajeev <atrajeev@xxxxxxxxxxxxxxxxxx> Date: Thu, 17 Jun 2021 13:55:06 -0400 Subject: powerpc/perf: Fix crash in perf_instruction_pointer() when ppmu is not set 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 Patches currently in stable-queue which might be from atrajeev@xxxxxxxxxxxxxxxxxx are queue-5.12/powerpc-perf-fix-crash-in-perf_instruction_pointer-when-ppmu-is-not-set.patch