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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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