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SubjectRe: [perf] fuzzer triggers unchecked MSR access error: WRMSR to 0x318
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);
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