Commit fb88707d authored by Oliver Upton's avatar Oliver Upton Committed by Marc Zyngier
Browse files

KVM: arm64: Use a maple tree to represent the SMCCC filter 



Maple tree is an efficient B-tree implementation that is intended for
storing non-overlapping intervals. Such a data structure is a good fit
for the SMCCC filter as it is desirable to sparsely allocate the 32 bit
function ID space.

To that end, add a maple tree to kvm_arch and correctly init/teardown
along with the VM. Wire in a test against the hypercall filter for HVCs
which does nothing until the controls are exposed to userspace.

Signed-off-by: default avatarOliver Upton <oliver.upton@linux.dev>
Signed-off-by: default avatarMarc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20230404154050.2270077-8-oliver.upton@linux.dev
parent a8308b3f

arch/arm64/include/asm/kvm_host.h

+4 −1
Original line number Diff line number Diff line
@@ -16,6 +16,7 @@ 
#include <linux/types.h>

#include <linux/jump_label.h>

#include <linux/kvm_types.h>

#include <linux/maple_tree.h>

#include <linux/percpu.h>

#include <linux/psci.h>

#include <asm/arch_gicv3.h>
@@ -221,7 +222,8 @@ struct kvm_arch { 
#define KVM_ARCH_FLAG_EL1_32BIT				4

	/* PSCI SYSTEM_SUSPEND enabled for the guest */

#define KVM_ARCH_FLAG_SYSTEM_SUSPEND_ENABLED		5



	/* SMCCC filter initialized for the VM */

#define KVM_ARCH_FLAG_SMCCC_FILTER_CONFIGURED		6

	unsigned long flags;



	/*
@@ -242,6 +244,7 @@ struct kvm_arch { 


	/* Hypercall features firmware registers' descriptor */

	struct kvm_smccc_features smccc_feat;

	struct maple_tree smccc_filter;



	/*

	 * For an untrusted host VM, 'pkvm.handle' is used to lookup

arch/arm64/kvm/arm.c

+2 −0
Original line number Diff line number Diff line
@@ -192,6 +192,8 @@ void kvm_arch_destroy_vm(struct kvm *kvm) 
	kvm_destroy_vcpus(kvm);



	kvm_unshare_hyp(kvm, kvm + 1);



	kvm_arm_teardown_hypercalls(kvm);

}



int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)

arch/arm64/kvm/hypercalls.c

+57 −0
Original line number Diff line number Diff line
@@ -121,8 +121,58 @@ static bool kvm_smccc_test_fw_bmap(struct kvm_vcpu *vcpu, u32 func_id) 
	}

}



#define SMCCC_ARCH_RANGE_BEGIN	ARM_SMCCC_VERSION_FUNC_ID

#define SMCCC_ARCH_RANGE_END				\

	ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL,		\

			   ARM_SMCCC_SMC_32,		\

			   0, ARM_SMCCC_FUNC_MASK)



static void init_smccc_filter(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

	 * to the guest.

	 */

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

			       SMCCC_ARCH_RANGE_BEGIN, SMCCC_ARCH_RANGE_END,

			       xa_mk_value(KVM_SMCCC_FILTER_HANDLE),

			       GFP_KERNEL_ACCOUNT);

	WARN_ON_ONCE(r);

}



static u8 kvm_smccc_filter_get_action(struct kvm *kvm, u32 func_id)

{

	unsigned long idx = func_id;

	void *val;



	if (!test_bit(KVM_ARCH_FLAG_SMCCC_FILTER_CONFIGURED, &kvm->arch.flags))

		return KVM_SMCCC_FILTER_HANDLE;



	/*

	 * But where's the error handling, you say?

	 *

	 * mt_find() returns NULL if no entry was found, which just so happens

	 * to match KVM_SMCCC_FILTER_HANDLE.

	 */

	val = mt_find(&kvm->arch.smccc_filter, &idx, idx);

	return xa_to_value(val);

}



static u8 kvm_smccc_get_action(struct kvm_vcpu *vcpu, u32 func_id)

{

	/*

	 * Intervening actions in the SMCCC filter take precedence over the

	 * pseudo-firmware register bitmaps.

	 */

	u8 action = kvm_smccc_filter_get_action(vcpu->kvm, func_id);

	if (action != KVM_SMCCC_FILTER_HANDLE)

		return action;



	if (kvm_smccc_test_fw_bmap(vcpu, func_id) ||

	    kvm_smccc_default_allowed(func_id))

		return KVM_SMCCC_FILTER_HANDLE;
@@ -263,6 +313,13 @@ void kvm_arm_init_hypercalls(struct kvm *kvm) 
	smccc_feat->std_bmap = KVM_ARM_SMCCC_STD_FEATURES;

	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);

}



void kvm_arm_teardown_hypercalls(struct kvm *kvm)

{

	mtree_destroy(&kvm->arch.smccc_filter);

}



int kvm_arm_get_fw_num_regs(struct kvm_vcpu *vcpu)

include/kvm/arm_hypercalls.h

+1 −0
Original line number Diff line number Diff line
@@ -43,6 +43,7 @@ static inline void smccc_set_retval(struct kvm_vcpu *vcpu, 
struct kvm_one_reg;



void kvm_arm_init_hypercalls(struct kvm *kvm);

void kvm_arm_teardown_hypercalls(struct kvm *kvm);

int kvm_arm_get_fw_num_regs(struct kvm_vcpu *vcpu);

int kvm_arm_copy_fw_reg_indices(struct kvm_vcpu *vcpu, u64 __user *uindices);

int kvm_arm_get_fw_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg);