[PATCH 4.9 024/107] perf/x86/amd/ibs: Dont access non-started event

From: Greg Kroah-Hartman
Date: Mon Sep 03 2018 - 13:04:17 EST


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);