[tip: perf/urgent] perf/x86: Fix out of bound MSR access

[tip-bot2 for Peter Zijlstra]

The following commit has been merged into the perf/urgent branch of tip:

Commit-ID:     f4b4b45652578357031fbbef7f7a1b04f6fa2dc3
Gitweb:        https://git.kernel.org/tip/f4b4b45652578357031fbbef7f7a1b04f6fa2dc3
Author:        Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate:    Thu, 29 Jul 2021 11:14:57 +02:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Wed, 04 Aug 2021 15:16:33 +02:00

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@xxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Tested-by: Vince Weaver <vincent.weaver@xxxxxxxxx>
Tested-by: Like Xu <likexu@xxxxxxxxxxx>
Link: https://lkml.kernel.org/r/YQJxka3dxgdIdebG@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
---
 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 1eb4513..3092fbf 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) >= 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);