/*
 * Copyright (c) 2018 Atmosphère-NX
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms and conditions of the GNU General Public License,
 * version 2, as published by the Free Software Foundation.
 *
 * This program is distributed in the hope it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
 * more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
#include <stdatomic.h>
#include <stdint.h>

#include "utils.h"
#include "memory_map.h"

#include "configitem.h"
#include "cpu_context.h"
#include "synchronization.h"
#include "masterkey.h"
#include "mc.h"
#include "memory_map.h"
#include "pmc.h"
#include "randomcache.h"
#include "sealedkeys.h"
#include "smc_api.h"
#include "smc_user.h"
#include "se.h"
#include "userpage.h"
#include "titlekey.h"
#include "lp0.h"
#include "exocfg.h"

#define SMC_USER_HANDLERS 0x13
#define SMC_PRIV_HANDLERS 0x9

#define DEBUG_LOG_SMCS 0
#define DEBUG_PANIC_ON_FAILURE 0

/* User SMC prototypes */
uint32_t smc_set_config_user(smc_args_t *args);
uint32_t smc_get_config_user(smc_args_t *args);
uint32_t smc_check_status(smc_args_t *args);
uint32_t smc_get_result(smc_args_t *args);
uint32_t smc_exp_mod(smc_args_t *args);
uint32_t smc_get_random_bytes_for_user(smc_args_t *args);
uint32_t smc_generate_aes_kek(smc_args_t *args);
uint32_t smc_load_aes_key(smc_args_t *args);
uint32_t smc_crypt_aes(smc_args_t *args);
uint32_t smc_generate_specific_aes_key(smc_args_t *args);
uint32_t smc_compute_cmac(smc_args_t *args);
uint32_t smc_load_rsa_oaep_key(smc_args_t *args);
uint32_t smc_decrypt_rsa_private_key(smc_args_t *args);
uint32_t smc_load_secure_exp_mod_key(smc_args_t *args);
uint32_t smc_secure_exp_mod(smc_args_t *args);
uint32_t smc_unwrap_rsa_oaep_wrapped_titlekey(smc_args_t *args);
uint32_t smc_load_titlekey(smc_args_t *args);
uint32_t smc_unwrap_aes_wrapped_titlekey(smc_args_t *args);

/* 5.x SMC prototypes. */
uint32_t smc_encrypt_rsa_key_for_import(smc_args_t *args);
uint32_t smc_decrypt_or_import_rsa_key(smc_args_t *args);

/* Privileged SMC prototypes */
uint32_t smc_cpu_suspend(smc_args_t *args);
uint32_t smc_cpu_off(smc_args_t *args);
uint32_t smc_cpu_on(smc_args_t *args);
uint32_t smc_get_config_priv(smc_args_t *args);
uint32_t smc_get_random_bytes_for_priv(smc_args_t *args);
uint32_t smc_panic(smc_args_t *args);
uint32_t smc_configure_carveout(smc_args_t *args);
uint32_t smc_read_write_register(smc_args_t *args);

typedef struct {
    uint32_t id;
    uint32_t (*handler)(smc_args_t *args);
} smc_table_entry_t;

typedef struct {
    smc_table_entry_t *handlers;
    uint32_t num_handlers;
} smc_table_t;

static smc_table_entry_t g_smc_user_table[SMC_USER_HANDLERS] = {
    {0, NULL},
    {0xC3000401, smc_set_config_user},
    {0xC3000002, smc_get_config_user},
    {0xC3000003, smc_check_status},
    {0xC3000404, smc_get_result},
    {0xC3000E05, smc_exp_mod},
    {0xC3000006, smc_get_random_bytes_for_user},
    {0xC3000007, smc_generate_aes_kek},
    {0xC3000008, smc_load_aes_key},
    {0xC3000009, smc_crypt_aes},
    {0xC300000A, smc_generate_specific_aes_key},
    {0xC300040B, smc_compute_cmac},
    {0xC300100C, smc_load_rsa_oaep_key},
    {0xC300100D, smc_decrypt_rsa_private_key},
    {0xC300100E, smc_load_secure_exp_mod_key},
    {0xC300060F, smc_secure_exp_mod},
    {0xC3000610, smc_unwrap_rsa_oaep_wrapped_titlekey},
    {0xC3000011, smc_load_titlekey},
    {0xC3000012, smc_unwrap_aes_wrapped_titlekey}
};

static smc_table_entry_t g_smc_priv_table[SMC_PRIV_HANDLERS] = {
    {0, NULL},
    {0xC4000001, smc_cpu_suspend},
    {0x84000002, smc_cpu_off},
    {0xC4000003, smc_cpu_on},
    {0xC3000004, smc_get_config_priv},
    {0xC3000005, smc_get_random_bytes_for_priv},
    {0xC3000006, smc_panic},
    {0xC3000007, smc_configure_carveout},
    {0xC3000008, smc_read_write_register}
};

static smc_table_t g_smc_tables[2] = {
    { /* SMC_HANDLER_USER */
        g_smc_user_table,
        SMC_USER_HANDLERS
    },
    { /* SMC_HANDLER_PRIV */
        g_smc_priv_table,
        SMC_PRIV_HANDLERS
    }
};

static atomic_flag g_is_user_smc_in_progress = ATOMIC_FLAG_INIT;
static atomic_flag g_is_priv_smc_in_progress = ATOMIC_FLAG_INIT;

/* Global for smc_configure_carveout. */
static bool g_configured_carveouts[2] = {false, false};

static bool g_has_suspended = false;
void set_suspend_for_debug(void) {
    g_has_suspended = true;
}

void set_version_specific_smcs(void) {
    switch (exosphere_get_target_firmware()) {
        case EXOSPHERE_TARGET_FIRMWARE_100:
            /* 1.0.0 doesn't have ConfigureCarveout or ReadWriteRegister. */
            g_smc_priv_table[7].handler = NULL;
            g_smc_priv_table[8].handler = NULL;
            /* 1.0.0 doesn't have UnwrapAesWrappedTitlekey. */
            g_smc_user_table[0x12].handler = NULL;
            break;
        case EXOSPHERE_TARGET_FIRMWARE_200:
        case EXOSPHERE_TARGET_FIRMWARE_300:
        case EXOSPHERE_TARGET_FIRMWARE_400:
            /* Do nothing. */
            break;
        case EXOSPHERE_TARGET_FIRMWARE_500:
        case EXOSPHERE_TARGET_FIRMWARE_600:
        case EXOSPHERE_TARGET_FIRMWARE_620:
            /* No more LoadSecureExpModKey. */
            g_smc_user_table[0xE].handler = NULL;
            g_smc_user_table[0xC].id = 0xC300D60C;
            g_smc_user_table[0xC].handler = smc_encrypt_rsa_key_for_import;
            g_smc_user_table[0xD].handler = smc_decrypt_or_import_rsa_key;
            break;
        default:
            panic_predefined(0xA);
    }
}


uintptr_t get_smc_core012_stack_address(void) {
    return TZRAM_GET_SEGMENT_ADDRESS(TZRAM_SEGMENT_ID_CORE012_STACK) + 0x1000;
}

uintptr_t get_exception_entry_stack_address(unsigned int core_id) {
    /* For core3, this is also the smc stack */
    if (core_id == 3) {
        return TZRAM_GET_SEGMENT_ADDRESS(TZRAM_SEGMENT_ID_CORE3_STACK) + 0x1000;
    }
    else {
        return TZRAM_GET_SEGMENT_ADDRESS(TZRAM_SEGEMENT_ID_SECMON_EVT) + 0x80 * (core_id + 1);
    }
}

bool try_set_user_smc_in_progress(void) {
    return lock_try_acquire(&g_is_user_smc_in_progress);
}
void set_user_smc_in_progress(void) {
    lock_acquire(&g_is_user_smc_in_progress);
}
void clear_user_smc_in_progress(void) {
    lock_release(&g_is_user_smc_in_progress);
}

/* Privileged SMC lock must be available to exceptions.s. */
void set_priv_smc_in_progress(void) {
    lock_acquire(&g_is_priv_smc_in_progress);
}
void clear_priv_smc_in_progress(void) {
    lock_release(&g_is_priv_smc_in_progress);
}

uint32_t (*g_smc_callback)(void *, uint64_t) = NULL;
uint64_t g_smc_callback_key = 0;

uint64_t try_set_smc_callback(uint32_t (*callback)(void *, uint64_t)) {
    uint64_t key;
    if (g_smc_callback_key) {
        return 0;
    }

    se_generate_random(KEYSLOT_SWITCH_RNGKEY, &key, sizeof(uint64_t));
    g_smc_callback_key = key;
    g_smc_callback = callback;
    return key;
}

void clear_smc_callback(uint64_t key) {
    if (g_smc_callback_key == key) {
        g_smc_callback_key = 0;
    }
}

_Atomic uint64_t num_smcs_called = 0;

void call_smc_handler(uint32_t handler_id, smc_args_t *args) {
    unsigned char smc_id;
    unsigned int result;
    unsigned int (*smc_handler)(smc_args_t *args);
    
    /* Validate top-level handler. */
    if (handler_id != SMC_HANDLER_USER && handler_id != SMC_HANDLER_PRIV) {
        generic_panic();
    }

    /* Validate core is appropriate for handler. */
    if (handler_id == SMC_HANDLER_USER && get_core_id() != 3) {
        /* USER SMCs must be called via svcCallSecureMonitor on core 3 (where spl runs) */
        generic_panic();
    }

    /* Validate sub-handler index */
    if ((smc_id = (unsigned char)args->X[0]) >= g_smc_tables[handler_id].num_handlers) {
        generic_panic();
    }

    /* Validate sub-handler */
    if (g_smc_tables[handler_id].handlers[smc_id].id != args->X[0]) {
        generic_panic();
    }

    /* Validate handler. */
    if ((smc_handler = g_smc_tables[handler_id].handlers[smc_id].handler) == NULL) {
        generic_panic();
    }
    
    bool is_aes_kek = handler_id == SMC_HANDLER_USER && args->X[0] == 0xC3000007;

#if DEBUG_LOG_SMCS  
    uint64_t num;  
    if (handler_id == SMC_HANDLER_USER) {
        num = atomic_fetch_add(&num_smcs_called, 1);
        *(volatile smc_args_t *)(get_iram_address_for_debug() + 0x100 + ((0x80 * num) & 0x3FFF)) = *args;
    }
#endif
     
    /* Call function. */
    args->X[0] = smc_handler(args);
#if DEBUG_LOG_SMCS    
    if (handler_id == SMC_HANDLER_USER) {
        *(volatile smc_args_t *)(get_iram_address_for_debug() + 0x100 + ((0x80 * num + 0x40) & 0x3FFF)) = *args;
        /*if (num >= 0x69) {
            panic(PANIC_REBOOT);
        }*/
    }
#endif
    
#if DEBUG_PANIC_ON_FAILURE
    if (args->X[0] && (!is_aes_kek || args->X[3] <= EXOSPHERE_TARGET_FIRMWARE_DEFAULT_FOR_DEBUG)) 
    {
        MAKE_REG32(get_iram_address_for_debug() + 0x4FF0) = handler_id;
        MAKE_REG32(get_iram_address_for_debug() + 0x4FF4) = smc_id;
        MAKE_REG32(get_iram_address_for_debug() + 0x4FF8) = get_core_id();
        *(volatile smc_args_t *)(get_iram_address_for_debug() + 0x4F00) = *args;
        panic(PANIC_REBOOT);
    }
#else
    (void)(is_aes_kek);
#endif
    (void)result; /* FIXME: result unused */
}

uint32_t smc_wrapper_sync(smc_args_t *args, uint32_t (*handler)(smc_args_t *)) {
    uint32_t result;
    if (!try_set_user_smc_in_progress()) {
        return 3;
    }
    result = handler(args);
    clear_user_smc_in_progress();
    return result;
}

uint32_t smc_wrapper_async(smc_args_t *args, uint32_t (*handler)(smc_args_t *), uint32_t (*callback)(void *, uint64_t)) {
    uint32_t result;
    uint64_t key;
    if (!try_set_user_smc_in_progress()) {
        return 3;
    }
    if ((key = try_set_smc_callback(callback)) != 0) {
        result = handler(args);
        if (result == 0) {
            /* Pass the status check key back to userland. */
            args->X[1] = key;
            /* Early return, leaving g_is_user_smc_in_progress locked */
            return result;
        } else {
            /* No status to check. */
            clear_smc_callback(key);
        }
    } else {
        /* smcCheckStatus needs to be called. */
        result = 3;
    }
    clear_user_smc_in_progress();
    return result;
}

uint32_t smc_set_config_user(smc_args_t *args) {
    /* Actual value presumed in X3 on hardware. */
    return configitem_set(false, (ConfigItem)args->X[1], args->X[3]);
}

uint32_t smc_get_config_user(smc_args_t *args) {
    uint64_t out_item = 0;
    uint32_t result;
    result = configitem_get(false, (ConfigItem)args->X[1], &out_item);
    args->X[1] = out_item;
    return result;
}

uint32_t smc_check_status(smc_args_t *args) {
    if (g_smc_callback_key == 0) {
        return 4;
    }

    if (args->X[1] != g_smc_callback_key) {
        return 5;
    }

    args->X[1] = g_smc_callback(NULL, 0);

    g_smc_callback_key = 0;
    return 0;
}

uint32_t smc_get_result(smc_args_t *args) {
    uint32_t status;
    unsigned char result_buf[0x400];
    upage_ref_t page_ref;

    void *user_address = (void *)args->X[2];

    if (g_smc_callback_key == 0) {
        return 4;
    }

    if (args->X[1] != g_smc_callback_key) {
        return 5;
    }

    /* Check result size */
    if (args->X[3] > 0x400) {
        return 2;
    }

    args->X[1] = g_smc_callback(result_buf, args->X[3]);
    g_smc_callback_key = 0;

    /* Initialize page reference. */
    if (upage_init(&page_ref, user_address) == 0) {
        return 2;
    }

    /* Copy result output back to user. */
    if (secure_copy_to_user(&page_ref, user_address, result_buf, (size_t)args->X[3]) == 0) {
        return 2;
    }

    return 0;
    (void)status; /* FIXME: status unused */
}

uint32_t smc_exp_mod_get_result(void *buf, uint64_t size) {
    if (get_exp_mod_done() != 1) {
        return 3;
    }

    if (size != 0x100) {
        return 2;
    }

    se_get_exp_mod_output(buf, 0x100);

    /* smc_exp_mod is done now. */
    clear_user_smc_in_progress();
    return 0;
}

uint32_t smc_exp_mod(smc_args_t *args) {
    return smc_wrapper_async(args, user_exp_mod, smc_exp_mod_get_result);
}

uint32_t smc_get_random_bytes_for_user(smc_args_t *args) {
    return smc_wrapper_sync(args, user_get_random_bytes);
}

uint32_t smc_generate_aes_kek(smc_args_t *args) {
    return smc_wrapper_sync(args, user_generate_aes_kek);
}

uint32_t smc_load_aes_key(smc_args_t *args) {
    return smc_wrapper_sync(args, user_load_aes_key);
}

uint32_t smc_crypt_aes_status_check(void *buf, uint64_t size) {
    /* Buf and size are unused. */
    if (get_crypt_aes_done() != 1) {
        return 3;
    }
    /* smc_crypt_aes is done now. */
    clear_user_smc_in_progress();
    return 0;
}

uint32_t smc_crypt_aes(smc_args_t *args) {
    return smc_wrapper_async(args, user_crypt_aes, smc_crypt_aes_status_check);
}

uint32_t smc_generate_specific_aes_key(smc_args_t *args) {
    return smc_wrapper_sync(args, user_generate_specific_aes_key);
}

uint32_t smc_compute_cmac(smc_args_t *args) {
    return smc_wrapper_sync(args, user_compute_cmac);
}

uint32_t smc_load_rsa_oaep_key(smc_args_t *args) {
    return smc_wrapper_sync(args, user_load_rsa_oaep_key);
}

uint32_t smc_decrypt_rsa_private_key(smc_args_t *args) {
    return smc_wrapper_sync(args, user_decrypt_rsa_private_key);
}

uint32_t smc_load_secure_exp_mod_key(smc_args_t *args) {
    return smc_wrapper_sync(args, user_load_secure_exp_mod_key);
}

uint32_t smc_secure_exp_mod(smc_args_t *args) {
    return smc_wrapper_async(args, user_secure_exp_mod, smc_exp_mod_get_result);
}

uint32_t smc_unwrap_rsa_oaep_wrapped_titlekey_get_result(void *buf, uint64_t size) {
    uint64_t *p_sealed_key = (uint64_t *)buf;
    uint8_t rsa_wrapped_titlekey[0x100];
    uint8_t aes_wrapped_titlekey[0x10];
    uint8_t titlekey[0x10];
    uint64_t sealed_titlekey[2];
    if (get_exp_mod_done() != 1) {
        return 3;
    }

    if (size != 0x10) {
        return 2;
    }

    se_get_exp_mod_output(rsa_wrapped_titlekey, 0x100);
    if (tkey_rsa_oaep_unwrap(aes_wrapped_titlekey, 0x10, rsa_wrapped_titlekey, 0x100) != 0x10) {
        /* Failed to extract RSA OAEP wrapped key. */
        clear_user_smc_in_progress();
        return 2;
    }

    tkey_aes_unwrap(titlekey, 0x10, aes_wrapped_titlekey, 0x10);
    seal_titlekey(sealed_titlekey, 0x10, titlekey, 0x10);

    p_sealed_key[0] = sealed_titlekey[0];
    p_sealed_key[1] = sealed_titlekey[1];

    /* smc_unwrap_rsa_oaep_wrapped_titlekey is done now. */
    clear_user_smc_in_progress();
    return 0;
}

uint32_t smc_unwrap_rsa_oaep_wrapped_titlekey(smc_args_t *args) {
    return smc_wrapper_async(args, user_unwrap_rsa_oaep_wrapped_titlekey, smc_unwrap_rsa_oaep_wrapped_titlekey_get_result);
}

uint32_t smc_load_titlekey(smc_args_t *args) {
    return smc_wrapper_sync(args, user_load_titlekey);
}

uint32_t smc_unwrap_aes_wrapped_titlekey(smc_args_t *args) {
    return smc_wrapper_sync(args, user_unwrap_aes_wrapped_titlekey);
}

uint32_t smc_encrypt_rsa_key_for_import(smc_args_t *args) {
    return smc_wrapper_sync(args, user_encrypt_rsa_key_for_import);
}

uint32_t smc_decrypt_or_import_rsa_key(smc_args_t *args) {
    return smc_wrapper_sync(args, user_decrypt_or_import_rsa_key);
}


uint32_t smc_cpu_on(smc_args_t *args) {
    return cpu_on((uint32_t)args->X[1], args->X[2], args->X[3]);
}

uint32_t smc_cpu_off(smc_args_t *args) {
    return cpu_off();
}

/* Wrapper for cpu_suspend */
uint32_t cpu_suspend_wrapper(smc_args_t *args) {
    return cpu_suspend(args->X[1], args->X[2], args->X[3]);
}

uint32_t smc_cpu_suspend(smc_args_t *args) {
    return smc_wrapper_sync(args, cpu_suspend_wrapper);
}

uint32_t smc_get_config_priv(smc_args_t *args) {
    uint64_t out_item = 0;
    uint32_t result;
    result = configitem_get(true, (ConfigItem)args->X[1], &out_item);
    args->X[1] = out_item;
    return result;
}

uint32_t smc_get_random_bytes_for_priv(smc_args_t *args) {
    /* This is an interesting SMC. */
    /* The kernel must NEVER be unable to get random bytes, if it needs them */
    /* As such: */

    uint32_t result;

    if (!try_set_user_smc_in_progress()) {
        if (args->X[1] > 0x38) {
            return 2;
        }
        /* Retrieve bytes from the cache. */
        size_t num_bytes = (size_t)args->X[1];
        randomcache_getbytes(&args->X[1], num_bytes);
        result = 0;
    } else {
        /* If the kernel isn't denied service by a usermode SMC, generate fresh random bytes. */
        result = user_get_random_bytes(args);
        /* Also, refill our cache while we have the chance in case we get denied later. */
        randomcache_refill();
        clear_user_smc_in_progress();
    }
    return result;
}

uint32_t smc_read_write_register(smc_args_t *args) {
    uint64_t address = args->X[1];
    uint32_t mask = (uint32_t)(args->X[2]);
    uint32_t value = (uint32_t)(args->X[3]);
    volatile uint32_t *p_mmio = NULL;
    /* Address must be aligned. */
    if (address & 3) {
        return 2;
    }
    /* Check for PMC registers. */
    if (0x7000E400 <= address && address <= 0x7000EFFF) {
        const uint8_t pmc_whitelist[0x28] = {
            0xB9, 0xF9, 0x07, 0x00, 0x00, 0x00, 0x80, 0x03,
            0x00, 0x00, 0x00, 0x17, 0x00, 0xC4, 0x07, 0x00,
            0x00, 0x00, 0x00, 0x00, 0x00, 0x20, 0x20, 0x00,
            0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
            0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x40, 0x00
        };
        /* Offset = Address - PMC_BASE */
        uint32_t offset = (uint32_t)(address - 0x7000E400);
        uint32_t wl_ind = (offset >> 5);
        /* If address is whitelisted, allow write. */
        if (wl_ind < sizeof(pmc_whitelist) && (pmc_whitelist[wl_ind] & (1 << ((offset >> 2) & 0x7)))) {
            p_mmio = (volatile uint32_t *)(PMC_BASE + offset);
        } else {
            return 2;
        }
    } else if (exosphere_get_target_firmware() >= EXOSPHERE_TARGET_FIRMWARE_400 && MMIO_GET_DEVICE_PA(MMIO_DEVID_MC) <= address &&
               address < MMIO_GET_DEVICE_PA(MMIO_DEVID_MC) + MMIO_GET_DEVICE_SIZE(MMIO_DEVID_MC)) {
        /* Memory Controller RW supported only on 4.0.0+ */
        const uint8_t mc_whitelist[0x68] = {
            0x9F, 0x31, 0x30, 0x00, 0xF0, 0xFF, 0xF7, 0x01,
            0xCD, 0xFE, 0xC0, 0xFE, 0x00, 0x00, 0x00, 0x00,
            0x03, 0x40, 0x73, 0x3E, 0x2F, 0x00, 0x00, 0x6E,
            0x30, 0x05, 0x06, 0xB0, 0x71, 0xC8, 0x43, 0x04,
            0x80, 0x1F, 0x08, 0x80, 0x03, 0x00, 0x0E, 0x00,
            0x08, 0x00, 0xE0, 0x00, 0x0E, 0x00, 0x00, 0x00,
            0x00, 0x00, 0x00, 0x30, 0xF0, 0x03, 0x03, 0x30,
            0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
            0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
            0x00, 0x00, 0x00, 0x31, 0x00, 0x40, 0x00, 0x00,
            0x00, 0x03, 0x00, 0x00, 0xE4, 0xFF, 0xFF, 0x01,
            0x00, 0x00, 0x00, 0x00, 0x0C, 0x00, 0xFE, 0x0F,
            0x01, 0x00, 0x80, 0x00, 0x00, 0x08, 0x00, 0x00
        };
        uint32_t offset = (uint32_t)(address - 0x70019000);
        uint32_t wl_ind = (offset >> 5);
        /* If address is whitelisted, allow write. */
        if (wl_ind < sizeof(mc_whitelist) && (mc_whitelist[wl_ind] & (1 << ((offset >> 2) & 0x7)))) {
            p_mmio = (volatile uint32_t *)(MMIO_GET_DEVICE_ADDRESS(MMIO_DEVID_MC) + offset);
        } else {
            /* These addresses are not allowed by the whitelist. */
            /* They correspond to SMMU DISABLE for the BPMP, and for APB-DMA. */
            /* However, smcReadWriteRegister returns 0 for these addresses despite not actually performing the write. */
            /* This is "probably" to fuck with hackers who got access to smcReadWriteRegister and are trying to get */
            /* control of the BPMP for jamais vu etc., since there's no other reason to return 0 despite failure. */
            if (address == 0x7001923C || address == 0x70019298) {
                return 0;
            }
            return 2;
        }
    }

    /* Perform actual write. */
    if (p_mmio != NULL) {
        uint32_t old_value;
        /* Write whole value. */
        if (mask == 0xFFFFFFFF) {
            old_value = 0;
        } else {
            old_value = *p_mmio;
        }
        if (mask) {
            *p_mmio = (old_value & ~mask) | (value & mask);
        }
        /* Return old value. */
        args->X[1] = old_value;
        return 0;
    }

    return 2;
}


uint32_t smc_configure_carveout(smc_args_t *args) {
    unsigned int carveout_id = (unsigned int)args->X[1];
    uint64_t address = args->X[2];
    uint64_t size = args->X[3];

    /* Ensure carveout isn't too big. */
    if (size > KERNEL_CARVEOUT_SIZE_MAX) {
        return 2;
    }
    
    /* Ensure validity of carveout index. */
    if (carveout_id > 1) {
        return 2;
    }

    /* Configuration is one-shot, and cannot be done multiple times. */
    if (exosphere_get_target_firmware() < EXOSPHERE_TARGET_FIRMWARE_300) { 
        if (g_configured_carveouts[carveout_id]) {
            return 2;
        }
    }

    configure_kernel_carveout(carveout_id + 4, address, size);
    g_configured_carveouts[carveout_id] = true;
    return 0;
}

uint32_t smc_panic(smc_args_t *args) {
    /* Swap RGB values from args. */
    uint32_t color = ((args->X[1] & 0xF) << 8) | ((args->X[1] & 0xF0)) | ((args->X[1] & 0xF00) >> 8);
    panic((color << 20) | 0x40);
}