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UPSTREAM: KVM: arm64: Fix race when enabling KVM_ARM_CAP_MTE

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When enabling KVM_CAP_ARM_MTE the ioctl checks that there are no VCPUs
created to ensure that the capability is enabled before the VM is
running. However no locks are held at that point so it is
(theoretically) possible for another thread in the VMM to create VCPUs
between the check and actually setting mte_enabled. Close the race by
taking kvm->lock.

Reported-by: Alexandru Elisei <alexandru.elisei@arm.com>
Fixes: 673638f434 ("KVM: arm64: Expose KVM_ARM_CAP_MTE")
Signed-off-by: Steven Price <steven.price@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210729160036.20433-1-steven.price@arm.com
(cherry picked from commit c4d7c51845)
Signed-off-by: Will Deacon <willdeacon@google.com>
Bug: 192636784
Change-Id: If572d9fa8fc2c7d955ba4ad174132506e6361a73
This commit is contained in:
Steven Price
2021-07-29 17:00:36 +01:00
committed by Will Deacon
parent a8a89c03a2
commit 725d80ded4
1 changed files with 8 additions and 4 deletions
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12
arch/arm64/kvm/arm.c
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@@ -94,10 +94,14 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
kvm->arch.return_nisv_io_abort_to_user = true;
break;
case KVM_CAP_ARM_MTE:
if (!system_supports_mte() || kvm->created_vcpus)
return -EINVAL;
r = 0;
kvm->arch.mte_enabled = true;
mutex_lock(&kvm->lock);
if (!system_supports_mte() || kvm->created_vcpus) {
r = -EINVAL;
} else {
r = 0;
kvm->arch.mte_enabled = true;
}
mutex_unlock(&kvm->lock);
break;
default:
r = -EINVAL;