From: Oliver Upton oupton@google.com
stable inclusion from linux-4.19.207 commit b6e5cd323d1d1537f450ab0d3e06811a868267c2
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[ Upstream commit 6826c6849b46aaa91300201213701eb861af4ba0 ]
The CPU_ON PSCI call takes a payload that KVM uses to configure a destination vCPU to run. This payload is non-architectural state and not exposed through any existing UAPI. Effectively, we have a race between CPU_ON and userspace saving/restoring a guest: if the target vCPU isn't ran again before the VMM saves its state, the requested PC and context ID are lost. When restored, the target vCPU will be runnable and start executing at its old PC.
We can avoid this race by making sure the reset payload is serviced before userspace can access a vCPU's state.
Fixes: 358b28f09f0a ("arm/arm64: KVM: Allow a VCPU to fully reset itself") Signed-off-by: Oliver Upton oupton@google.com Signed-off-by: Marc Zyngier maz@kernel.org Link: https://lore.kernel.org/r/20210818202133.1106786-3-oupton@google.com Signed-off-by: Sasha Levin sashal@kernel.org Signed-off-by: Yang Yingliang yangyingliang@huawei.com --- virt/kvm/arm/arm.c | 8 ++++++++ 1 file changed, 8 insertions(+)
diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c index b9aeed598a367..9879755f534c6 100644 --- a/virt/kvm/arm/arm.c +++ b/virt/kvm/arm/arm.c @@ -1217,6 +1217,14 @@ long kvm_arch_vcpu_ioctl(struct file *filp, if (copy_from_user(®, argp, sizeof(reg))) break;
+ /* + * We could owe a reset due to PSCI. Handle the pending reset + * here to ensure userspace register accesses are ordered after + * the reset. + */ + if (kvm_check_request(KVM_REQ_VCPU_RESET, vcpu)) + kvm_reset_vcpu(vcpu); + if (ioctl == KVM_SET_ONE_REG) r = kvm_arm_set_reg(vcpu, ®); else