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    Subject[PATCH 4.14 042/165] perf/x86/amd/ibs: Dont access non-started event
    Date
    4.14-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Thomas Gleixner <tglx@linutronix.de>

    [ 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@molgen.mpg.de>
    Tested-by: Paul Menzel <pmenzel@molgen.mpg.de>
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
    Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: Jiri Olsa <jolsa@redhat.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Paul Menzel <pmenzel+linux-x86@molgen.mpg.de>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Stephane Eranian <eranian@google.com>
    Cc: Vince Weaver <vincent.weaver@maine.edu>
    Link: http://lkml.kernel.org/r/alpine.DEB.2.21.1807200958390.1580@nanos.tec.linutronix.de
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    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
    @@ -579,7 +579,7 @@ 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;
    @@ -602,6 +602,10 @@ fail:
    return 0;
    }

    + if (WARN_ON_ONCE(!event))
    + goto fail;
    +
    + hwc = &event->hw;
    msr = hwc->config_base;
    buf = ibs_data.regs;
    rdmsrl(msr, *buf);

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