4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Thomas Gleixner <tglx@xxxxxxxxxxxxx> [ Upstream commit d2753e6b4882a637a0e8fb3b9c2e15f33265300e ] Paul Menzel reported the following bug: > Enabling the undefined behavior sanitizer and building GNU/Linux 4.18-rc5+ > (with some unrelated commits) with GCC 8.1.0 from Debian Sid/unstable, the > warning below is shown. > > > [ 2.111913] > > ================================================================================ > > [ 2.111917] UBSAN: Undefined behaviour in arch/x86/events/amd/ibs.c:582:24 > > [ 2.111919] member access within null pointer of type 'struct perf_event' > > [ 2.111926] CPU: 0 PID: 144 Comm: udevadm Not tainted 4.18.0-rc5-00316-g4864b68cedf2 #104 > > [ 2.111928] Hardware name: ASROCK E350M1/E350M1, BIOS TIMELESS 01/01/1970 > > [ 2.111930] Call Trace: > > [ 2.111943] dump_stack+0x55/0x89 > > [ 2.111949] ubsan_epilogue+0xb/0x33 > > [ 2.111953] handle_null_ptr_deref+0x7f/0x90 > > [ 2.111958] __ubsan_handle_type_mismatch_v1+0x55/0x60 > > [ 2.111964] perf_ibs_handle_irq+0x596/0x620 The code dereferences event before checking the STARTED bit. Patch below should cure the issue. The warning should not trigger, if I analyzed the thing correctly. (And Paul's testing confirms this.) Reported-by: Paul Menzel <pmenzel@xxxxxxxxxxxxx> Tested-by: Paul Menzel <pmenzel@xxxxxxxxxxxxx> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx> Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx> Cc: Borislav Petkov <bp@xxxxxxxxx> Cc: Jiri Olsa <jolsa@xxxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Paul Menzel <pmenzel+linux-x86@xxxxxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Stephane Eranian <eranian@xxxxxxxxxx> Cc: Vince Weaver <vincent.weaver@xxxxxxxxx> Link: http://lkml.kernel.org/r/alpine.DEB.2.21.1807200958390.1580@xxxxxxxxxxxxxxxxxxxxxxx Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/x86/events/amd/ibs.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) --- a/arch/x86/events/amd/ibs.c +++ b/arch/x86/events/amd/ibs.c @@ -578,7 +578,7 @@ static int perf_ibs_handle_irq(struct pe { struct cpu_perf_ibs *pcpu = this_cpu_ptr(perf_ibs->pcpu); struct perf_event *event = pcpu->event; - struct hw_perf_event *hwc = &event->hw; + struct hw_perf_event *hwc; struct perf_sample_data data; struct perf_raw_record raw; struct pt_regs regs; @@ -601,6 +601,10 @@ fail: return 0; } + if (WARN_ON_ONCE(!event)) + goto fail; + + hwc = &event->hw; msr = hwc->config_base; buf = ibs_data.regs; rdmsrl(msr, *buf);
