Commit d34b7648 authored by Oliver Upton's avatar Oliver Upton
Browse files

KVM: arm64: Only insert reserved ranges when SMCCC filter is used 



The reserved ranges are only useful for preventing userspace from
adding a rule that intersects with functions we must handle in KVM. If
userspace never writes to the SMCCC filter than this is all just wasted
work/memory.

Insert reserved ranges on the first call to KVM_ARM_VM_SMCCC_FILTER.

Reviewed-by: default avatarMarc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20231004234947.207507-3-oliver.upton@linux.dev


Signed-off-by: default avatarOliver Upton <oliver.upton@linux.dev>
parent bb17fb31

arch/arm64/kvm/hypercalls.c

+16 −6
Original line number Diff line number Diff line
@@ -133,12 +133,10 @@ static bool kvm_smccc_test_fw_bmap(struct kvm_vcpu *vcpu, u32 func_id) 
						   ARM_SMCCC_SMC_64,		\

						   0, ARM_SMCCC_FUNC_MASK)



static void init_smccc_filter(struct kvm *kvm)

static int kvm_smccc_filter_insert_reserved(struct kvm *kvm)

{

	int r;



	mt_init(&kvm->arch.smccc_filter);



	/*

	 * Prevent userspace from handling any SMCCC calls in the architecture

	 * range, avoiding the risk of misrepresenting Spectre mitigation status
@@ -148,14 +146,20 @@ static void init_smccc_filter(struct kvm *kvm) 
			       SMC32_ARCH_RANGE_BEGIN, SMC32_ARCH_RANGE_END,

			       xa_mk_value(KVM_SMCCC_FILTER_HANDLE),

			       GFP_KERNEL_ACCOUNT);

	WARN_ON_ONCE(r);

	if (r)

		goto out_destroy;



	r = mtree_insert_range(&kvm->arch.smccc_filter,

			       SMC64_ARCH_RANGE_BEGIN, SMC64_ARCH_RANGE_END,

			       xa_mk_value(KVM_SMCCC_FILTER_HANDLE),

			       GFP_KERNEL_ACCOUNT);

	WARN_ON_ONCE(r);

	if (r)

		goto out_destroy;



	return 0;

out_destroy:

	mtree_destroy(&kvm->arch.smccc_filter);

	return r;

}



static bool kvm_smccc_filter_configured(struct kvm *kvm)
@@ -189,6 +193,12 @@ static int kvm_smccc_set_filter(struct kvm *kvm, struct kvm_smccc_filter __user 
		goto out_unlock;

	}



	if (!kvm_smccc_filter_configured(kvm)) {

		r = kvm_smccc_filter_insert_reserved(kvm);

		if (WARN_ON_ONCE(r))

			goto out_unlock;

	}



	r = mtree_insert_range(&kvm->arch.smccc_filter, start, end,

			       xa_mk_value(filter.action), GFP_KERNEL_ACCOUNT);

	if (r)
@@ -392,7 +402,7 @@ void kvm_arm_init_hypercalls(struct kvm *kvm) 
	smccc_feat->std_hyp_bmap = KVM_ARM_SMCCC_STD_HYP_FEATURES;

	smccc_feat->vendor_hyp_bmap = KVM_ARM_SMCCC_VENDOR_HYP_FEATURES;



	init_smccc_filter(kvm);

	mt_init(&kvm->arch.smccc_filter);

}



void kvm_arm_teardown_hypercalls(struct kvm *kvm)