perf/x86: Fix out of bound MSR access

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

The problem being that it doesn't filter out all fake counters, in
specific the above (erroneously) tries to use FIXED_BTS. Limit the
fixed counters indexes to the hardware supplied number.

Reported-by: Vince Weaver <vincent.weaver@maine.edu>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Vince Weaver <vincent.weaver@maine.edu>
Tested-by: Like Xu <likexu@tencent.com>
Link: https://lkml.kernel.org/r/YQJxka3dxgdIdebG@hirez.programming.kicks-ass.net

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index 1eb4513..3092fbf 100644 (file)
--- 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) >= hybrid(cpuc->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);