arch/arm64/kvm/hyp/nvhe/modules.c

/* SPDX-License-Identifier: GPL-2.0-only */
/*
 * Copyright (C) 2022 Google LLC
 */
#include <asm/kvm_host.h>
#include <asm/kvm_pkvm_module.h>

#include <nvhe/mem_protect.h>
#include <nvhe/modules.h>
#include <nvhe/mm.h>
#include <nvhe/serial.h>
#include <nvhe/spinlock.h>
#include <nvhe/trap_handler.h>

static void __kvm_flush_dcache_to_poc(void *addr, size_t size)
{
	kvm_flush_dcache_to_poc((unsigned long)addr, (unsigned long)size);
}

DEFINE_HYP_SPINLOCK(modules_lock);

bool __pkvm_modules_enabled __ro_after_init;

void pkvm_modules_lock(void)
{
	hyp_spin_lock(&modules_lock);
}

void pkvm_modules_unlock(void)
{
	hyp_spin_unlock(&modules_lock);
}

bool pkvm_modules_enabled(void)
{
	return __pkvm_modules_enabled;
}

int __pkvm_close_module_registration(void)
{
	int ret;

	pkvm_modules_lock();
	ret = __pkvm_modules_enabled ? 0 : -EACCES;
	if (!ret) {
		void *addr = hyp_fixmap_map(__hyp_pa(&__pkvm_modules_enabled));
		*(bool *)addr = false;
		hyp_fixmap_unmap();
	}
	pkvm_modules_unlock();

	/* The fuse is blown! No way back until reset */
	return ret;
}

const struct pkvm_module_ops module_ops = {
	.create_private_mapping = __pkvm_create_private_mapping,
	.register_serial_driver = __pkvm_register_serial_driver,
	.puts = hyp_puts,
	.putx64 = hyp_putx64,
	.fixmap_map = hyp_fixmap_map,
	.fixmap_unmap = hyp_fixmap_unmap,
	.flush_dcache_to_poc = __kvm_flush_dcache_to_poc,
	.register_host_perm_fault_handler = hyp_register_host_perm_fault_handler,
	.protect_host_page = hyp_protect_host_page,
};

int __pkvm_init_module(void *module_init)
{
	int (*do_module_init)(const struct pkvm_module_ops *ops) = module_init;
	int ret;

	pkvm_modules_lock();
	if (!pkvm_modules_enabled()) {
		ret = -EACCES;
		goto err;
	}
	ret = do_module_init(&module_ops);
err:
	pkvm_modules_unlock();

	return ret;
}

#define MAX_DYNAMIC_HCALLS 128

atomic_t num_dynamic_hcalls = ATOMIC_INIT(0);
DEFINE_HYP_SPINLOCK(dyn_hcall_lock);

static dyn_hcall_t host_dynamic_hcalls[MAX_DYNAMIC_HCALLS];

int handle_host_dynamic_hcall(struct kvm_cpu_context *host_ctxt)
{
	DECLARE_REG(unsigned long, id, host_ctxt, 0);
	dyn_hcall_t hfn;
	int dyn_id;

	/*
	 * TODO: static key to protect when no dynamic hcall is registered?
	 */

	dyn_id = (int)(id - KVM_HOST_SMCCC_ID(0)) -
		 __KVM_HOST_SMCCC_FUNC___dynamic_hcalls;
	if (dyn_id < 0)
		return HCALL_UNHANDLED;

	cpu_reg(host_ctxt, 0) = SMCCC_RET_NOT_SUPPORTED;

	/*
	 * Order access to num_dynamic_hcalls and host_dynamic_hcalls. Paired
	 * with __pkvm_register_hcall().
	 */
	if (dyn_id >= atomic_read_acquire(&num_dynamic_hcalls))
		goto end;

	hfn = READ_ONCE(host_dynamic_hcalls[dyn_id]);
	if (!hfn)
		goto end;

	cpu_reg(host_ctxt, 0) = SMCCC_RET_SUCCESS;
	hfn(host_ctxt);
end:
	return HCALL_HANDLED;
}

int __pkvm_register_hcall(unsigned long hvn_hyp_va)
{
	dyn_hcall_t hfn = (void *)hvn_hyp_va;
	int reserved_id, ret;

	pkvm_modules_lock();
	if (!pkvm_modules_enabled()) {
		ret = -EACCES;
		goto err;
	}

	hyp_spin_lock(&dyn_hcall_lock);

	reserved_id = atomic_read(&num_dynamic_hcalls);

	if (reserved_id >= MAX_DYNAMIC_HCALLS) {
		ret = -ENOMEM;
		goto err_hcall_unlock;
	}

	WRITE_ONCE(host_dynamic_hcalls[reserved_id], hfn);

	/*
	 * Order access to num_dynamic_hcalls and host_dynamic_hcalls. Paired
	 * with handle_host_dynamic_hcall.
	 */
	atomic_set_release(&num_dynamic_hcalls, reserved_id + 1);

	ret = reserved_id + __KVM_HOST_SMCCC_FUNC___dynamic_hcalls;
err_hcall_unlock:
	hyp_spin_unlock(&dyn_hcall_lock);
err:
	pkvm_modules_unlock();

	return ret;
};