linux-kernel - Re: perf: perf_fuzzer crashes on Pentium 4 systems

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Date:   Wed, 3 Apr 2019 23:31:44 +0300
From:   Cyrill Gorcunov <gorcunov@...il.com>
To:     Vince Weaver <vincent.weaver@...ne.edu>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jiri Olsa <jolsa@...hat.com>,
        Stephane Eranian <eranian@...gle.com>
Subject: Re: perf: perf_fuzzer crashes on Pentium 4 systems

On Wed, Apr 03, 2019 at 10:19:44PM +0300, Cyrill Gorcunov wrote:
> 
> You know, seems I got what happened -- p4_general_events do
> not cover all general events, they stop at PERF_COUNT_HW_BUS_CYCLES,
> while more 3 general event left. This is 'cause I've not been following
> pmu evolution in code. I will try to cover this events hopefully more
> less soon and send you a patch to test (if you don't mind).

Still this should not cause nil deref, continue investigating. Vince
could oyu please apply the patch below, I doubt if it help with nil
issue but worth having anyway
---
From: Cyrill Gorcunov <gorcunov@...il.com>
Subject: [PATCH] perf/x86/intel/p4: Limit p4_general_events down to real ones

p4_general_events are allocated up to PERF_COUNT_HW_MAX while this constant
is bigger than the number of general events we do support by now. Thus the
all other entries are equal to zero and maps to P4_EVENT_TC_DELIVER_MODE
which is wrong of course. Instead drop off PERF_COUNT_HW_MAX constant
from declaration, we use ARRAY_SIZE for max_events.

Signed-off-by: Cyrill Gorcunov <gorcunov@...il.com>
---
 arch/x86/events/intel/p4.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-tip.git/arch/x86/events/intel/p4.c
===================================================================
--- linux-tip.git.orig/arch/x86/events/intel/p4.c
+++ linux-tip.git/arch/x86/events/intel/p4.c
@@ -648,7 +648,7 @@ static u64 p4_get_alias_event(u64 config
 	return config_match | (config & P4_CONFIG_EVENT_ALIAS_IMMUTABLE_BITS);
 }
 
-static u64 p4_general_events[PERF_COUNT_HW_MAX] = {
+static u64 p4_general_events[] = {
   /* non-halted CPU clocks */
   [PERF_COUNT_HW_CPU_CYCLES] =
 	p4_config_pack_escr(P4_ESCR_EVENT(P4_EVENT_GLOBAL_POWER_EVENTS)		|