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From: Peter Zijlstra <peterz@infradead.org>
To: Vince Weaver <vincent.weaver@maine.edu>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
	"Liang, Kan" <kan.liang@intel.com>
Subject: Re: [perf] fuzzer triggers unchecked MSR access error: WRMSR to 0x318
Date: Thu, 29 Jul 2021 11:14:57 +0200	[thread overview]
Message-ID: <YQJxka3dxgdIdebG@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <37881148-a43e-5fd4-817c-a875adc7a15f@maine.edu>

On Wed, Jul 28, 2021 at 12:49:43PM -0400, Vince Weaver wrote:
> [32694.087403] unchecked MSR access error: WRMSR to 0x318 (tried to write 0x0000000000000000) at rIP: 0xffffffff8106f854 (native_write_msr+0x4/0x20)
> [32694.101374] Call Trace:
> [32694.103974]  perf_clear_dirty_counters+0x86/0x100

Hmm.. if I read this right that's MSR_ARCH_PERFMON_FIXED_CTR0 + i, given
that FIXED_CTR0 is 0x309 that gives i == 15, which is FIXED_BTS.

I'm thinking something like this ought to cure things.

---
 arch/x86/events/core.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index 1eb45139fcc6..04edf8017961 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -2489,13 +2489,15 @@ void perf_clear_dirty_counters(void)
 		return;
 
 	for_each_set_bit(i, cpuc->dirty, X86_PMC_IDX_MAX) {
-		/* Metrics and fake events don't have corresponding HW counters. */
-		if (is_metric_idx(i) || (i == INTEL_PMC_IDX_FIXED_VLBR))
-			continue;
-		else if (i >= INTEL_PMC_IDX_FIXED)
+		if (i >= INTEL_PMC_IDX_FIXED) {
+			/* Metrics and fake events don't have corresponding HW counters. */
+			if ((i - INTEL_PMC_IDX_FIXED) >= x86_pmu.num_counters_fixed)
+				continue;
+
 			wrmsrl(MSR_ARCH_PERFMON_FIXED_CTR0 + (i - INTEL_PMC_IDX_FIXED), 0);
-		else
+		} else {
 			wrmsrl(x86_pmu_event_addr(i), 0);
+		}
 	}
 
 	bitmap_zero(cpuc->dirty, X86_PMC_IDX_MAX);

  reply	other threads:[~2021-07-29  9:15 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-28 16:49 Vince Weaver
2021-07-29  9:14 ` Peter Zijlstra [this message]
2021-07-29 13:21   ` Liang, Kan
2021-07-29 15:30     ` Peter Zijlstra
2021-08-02 11:40       ` Like Xu
2021-07-29 16:54   ` Vince Weaver
2021-08-05  9:34   ` [tip: perf/urgent] perf/x86: Fix out of bound MSR access tip-bot2 for Peter Zijlstra

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