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KVM regularly introduces new hypercall services to the guests without any consent from the userspace. This means, the guests can observe hypercall services in and out as they migrate across various host kernel versions. This could be a major problem if the guest discovered a hypercall, started using it, and after getting migrated to an older kernel realizes that it's no longer available. Depending on how the guest handles the change, there's a potential chance that the guest would just panic. As a result, there's a need for the userspace to elect the services that it wishes the guest to discover. It can elect these services based on the kernels spread across its (migration) fleet. To remedy this, extend the existing firmware pseudo-registers, such as KVM_REG_ARM_PSCI_VERSION, but by creating a new COPROC register space for all the hypercall services available. These firmware registers are categorized based on the service call owners, but unlike the existing firmware pseudo-registers, they hold the features supported in the form of a bitmap. During the VM initialization, the registers are set to upper-limit of the features supported by the corresponding registers. It's expected that the VMMs discover the features provided by each register via GET_ONE_REG, and write back the desired values using SET_ONE_REG. KVM allows this modification only until the VM has started. Some of the standard features are not mapped to any bits of the registers. But since they can recreate the original problem of making it available without userspace's consent, they need to be explicitly added to the case-list in kvm_hvc_call_default_allowed(). Any function-id that's not enabled via the bitmap, or not listed in kvm_hvc_call_default_allowed, will be returned as SMCCC_RET_NOT_SUPPORTED to the guest. Older userspace code can simply ignore the feature and the hypercall services will be exposed unconditionally to the guests, thus ensuring backward compatibility. In this patch, the framework adds the register only for ARM's standard secure services (owner value 4). Currently, this includes support only for ARM True Random Number Generator (TRNG) service, with bit-0 of the register representing mandatory features of v1.0. Other services are momentarily added in the upcoming patches. Signed-off-by: Raghavendra Rao Ananta <rananta@google.com> Reviewed-by: Gavin Shan <gshan@redhat.com> [maz: reduced the scope of some helpers, tidy-up bitmap max values, dropped error-only fast path] Signed-off-by: Marc Zyngier <maz@kernel.org> Link: https://lore.kernel.org/r/20220502233853.1233742-3-rananta@google.com
52 lines
1.2 KiB
C
52 lines
1.2 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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/* Copyright (C) 2019 Arm Ltd. */
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#ifndef __KVM_ARM_HYPERCALLS_H
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#define __KVM_ARM_HYPERCALLS_H
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#include <asm/kvm_emulate.h>
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int kvm_hvc_call_handler(struct kvm_vcpu *vcpu);
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static inline u32 smccc_get_function(struct kvm_vcpu *vcpu)
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{
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return vcpu_get_reg(vcpu, 0);
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}
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static inline unsigned long smccc_get_arg1(struct kvm_vcpu *vcpu)
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{
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return vcpu_get_reg(vcpu, 1);
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}
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static inline unsigned long smccc_get_arg2(struct kvm_vcpu *vcpu)
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{
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return vcpu_get_reg(vcpu, 2);
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}
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static inline unsigned long smccc_get_arg3(struct kvm_vcpu *vcpu)
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{
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return vcpu_get_reg(vcpu, 3);
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}
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static inline void smccc_set_retval(struct kvm_vcpu *vcpu,
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unsigned long a0,
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unsigned long a1,
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unsigned long a2,
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unsigned long a3)
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{
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vcpu_set_reg(vcpu, 0, a0);
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vcpu_set_reg(vcpu, 1, a1);
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vcpu_set_reg(vcpu, 2, a2);
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vcpu_set_reg(vcpu, 3, a3);
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}
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struct kvm_one_reg;
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void kvm_arm_init_hypercalls(struct kvm *kvm);
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int kvm_arm_get_fw_num_regs(struct kvm_vcpu *vcpu);
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int kvm_arm_copy_fw_reg_indices(struct kvm_vcpu *vcpu, u64 __user *uindices);
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int kvm_arm_get_fw_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg);
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int kvm_arm_set_fw_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg);
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#endif
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