linux-kernel - [PATCH] KVM: arm/arm64: Assign pmc->idx before kvm_pmu_stop

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Date:   Wed, 17 Jul 2019 12:20:19 +0000
From:   Zenghui Yu <yuzenghui@...wei.com>
To:     <maz@...nel.org>, <kvmarm@...ts.cs.columbia.edu>,
        <linux-arm-kernel@...ts.infradead.org>
CC:     <marc.zyngier@....com>, <james.morse@....com>,
        <julien.thierry@....com>, <suzuki.poulose@....com>,
        <julien.thierry.kdev@...il.com>, <linux-kernel@...r.kernel.org>,
        <wanghaibin.wang@...wei.com>, <andrew.murray@....com>,
        Zenghui Yu <yuzenghui@...wei.com>
Subject: [PATCH] KVM: arm/arm64: Assign pmc->idx before kvm_pmu_stop_counter()

We use "pmc->idx" and the "chained" bitmap to determine if the pmc is
chained, in kvm_pmu_pmc_is_chained().  But idx might be uninitialized
(and random) when we doing this decision, through a KVM_ARM_VCPU_INIT
ioctl -> kvm_pmu_vcpu_reset(). And the test_bit() against this random
idx will potentially hit a KASAN BUG [1].

Fix it by moving the assignment of idx before kvm_pmu_stop_counter().

[1] https://www.spinics.net/lists/kvm-arm/msg36700.html

Fixes: 80f393a23be6 ("KVM: arm/arm64: Support chained PMU counters")
Suggested-by: Andrew Murray <andrew.murray@....com>
Cc: Marc Zyngier <maz@...nel.org>
Signed-off-by: Zenghui Yu <yuzenghui@...wei.com>
---
 virt/kvm/arm/pmu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/virt/kvm/arm/pmu.c b/virt/kvm/arm/pmu.c
index 3dd8238..521bfdd 100644
--- a/virt/kvm/arm/pmu.c
+++ b/virt/kvm/arm/pmu.c
@@ -225,8 +225,8 @@ void kvm_pmu_vcpu_reset(struct kvm_vcpu *vcpu)
 	struct kvm_pmu *pmu = &vcpu->arch.pmu;
 
 	for (i = 0; i < ARMV8_PMU_MAX_COUNTERS; i++) {
-		kvm_pmu_stop_counter(vcpu, &pmu->pmc[i]);
 		pmu->pmc[i].idx = i;
+		kvm_pmu_stop_counter(vcpu, &pmu->pmc[i]);
 	}
 
 	bitmap_zero(vcpu->arch.pmu.chained, ARMV8_PMU_MAX_COUNTER_PAIRS);
-- 
1.8.3.1