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SubjectRe: UBSAN: Undefined behaviour in arch/x86/events/amd/ibs.c:582:24: member access within null pointer of type 'struct perf_event'
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Dear Thomas,


Am 20.07.2018 um 10:39 schrieb Thomas Gleixner:

> On Fri, 20 Jul 2018, Paul Menzel wrote:
>> 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
>
> Right, 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. Emphasis on *should*

> 8<--------------------
> diff --git a/arch/x86/events/amd/ibs.c b/arch/x86/events/amd/ibs.c
> index 4b98101209a1..d50bb4dc0650 100644
> --- a/arch/x86/events/amd/ibs.c
> +++ b/arch/x86/events/amd/ibs.c
> @@ -579,7 +579,7 @@ static int perf_ibs_handle_irq(struct perf_ibs *perf_ibs, struct pt_regs *iregs)
> {
> 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;
> @@ -602,6 +602,10 @@ static int perf_ibs_handle_irq(struct perf_ibs *perf_ibs, struct pt_regs *iregs)
> return 0;
> }
>
> + if (WARN_ON_ONCE(!event))
> + goto fail;
> +
> + hwc = &event->hw;
> msr = hwc->config_base;
> buf = ibs_data.regs;
> rdmsrl(msr, *buf);

Thank you very much. The warning is gone after applying it.

Tested-by: Paul Menzel <pmenzel@molgen.mpg.de>


Kind regards,

Paul

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