FreeRTOS-Kernel/portable/ARMv8M/secure/context/secure_context.c

/*
 * FreeRTOS Kernel V10.4.3
 * Copyright (C) 2020 Amazon.com, Inc. or its affiliates.  All Rights Reserved.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy of
 * this software and associated documentation files (the "Software"), to deal in
 * the Software without restriction, including without limitation the rights to
 * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
 * the Software, and to permit persons to whom the Software is furnished to do so,
 * subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
 * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
 * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
 * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 *
 * https://www.FreeRTOS.org
 * https://github.com/FreeRTOS
 *
 * 1 tab == 4 spaces!
 */

/* Secure context includes. */
#include "secure_context.h"

/* Secure heap includes. */
#include "secure_heap.h"

/* Secure port macros. */
#include "secure_port_macros.h"

/**
 * @brief CONTROL value for privileged tasks.
 *
 * Bit[0] - 0 --> Thread mode is privileged.
 * Bit[1] - 1 --> Thread mode uses PSP.
 */
#define securecontextCONTROL_VALUE_PRIVILEGED      0x02

/**
 * @brief CONTROL value for un-privileged tasks.
 *
 * Bit[0] - 1 --> Thread mode is un-privileged.
 * Bit[1] - 1 --> Thread mode uses PSP.
 */
#define securecontextCONTROL_VALUE_UNPRIVILEGED    0x03
/*-----------------------------------------------------------*/

/**
 * @brief Structure to represent secure context.
 *
 * @note Since stack grows down, pucStackStart is the highest address while
 * pucStackLimit is the first addess of the allocated memory.
 */
typedef struct SecureContext
{
    uint8_t * pucCurrentStackPointer; /**< Current value of stack pointer (PSP). */
    uint8_t * pucStackLimit;          /**< Last location of the stack memory (PSPLIM). */
    uint8_t * pucStackStart;          /**< First location of the stack memory. */
} SecureContext_t;
/*-----------------------------------------------------------*/

secureportNON_SECURE_CALLABLE void SecureContext_Init( void )
{
    uint32_t ulIPSR;

    /* Read the Interrupt Program Status Register (IPSR) value. */
    secureportREAD_IPSR( ulIPSR );

    /* Do nothing if the processor is running in the Thread Mode. IPSR is zero
     * when the processor is running in the Thread Mode. */
    if( ulIPSR != 0 )
    {
        /* No stack for thread mode until a task's context is loaded. */
        secureportSET_PSPLIM( securecontextNO_STACK );
        secureportSET_PSP( securecontextNO_STACK );

        #if ( configENABLE_MPU == 1 )
            {
                /* Configure thread mode to use PSP and to be unprivileged. */
                secureportSET_CONTROL( securecontextCONTROL_VALUE_UNPRIVILEGED );
            }
        #else /* configENABLE_MPU */
            {
                /* Configure thread mode to use PSP and to be privileged.. */
                secureportSET_CONTROL( securecontextCONTROL_VALUE_PRIVILEGED );
            }
        #endif /* configENABLE_MPU */
    }
}
/*-----------------------------------------------------------*/

#if ( configENABLE_MPU == 1 )
    secureportNON_SECURE_CALLABLE SecureContextHandle_t SecureContext_AllocateContext( uint32_t ulSecureStackSize,
                                                                                       uint32_t ulIsTaskPrivileged )
#else /* configENABLE_MPU */
    secureportNON_SECURE_CALLABLE SecureContextHandle_t SecureContext_AllocateContext( uint32_t ulSecureStackSize )
#endif /* configENABLE_MPU */
{
    uint8_t * pucStackMemory = NULL;
    uint32_t ulIPSR;
    SecureContextHandle_t xSecureContextHandle = NULL;

    #if ( configENABLE_MPU == 1 )
        uint32_t * pulCurrentStackPointer = NULL;
    #endif /* configENABLE_MPU */

    /* Read the Interrupt Program Status Register (IPSR) value. */
    secureportREAD_IPSR( ulIPSR );

    /* Do nothing if the processor is running in the Thread Mode. IPSR is zero
     * when the processor is running in the Thread Mode. */
    if( ulIPSR != 0 )
    {
        /* Allocate the context structure. */
        xSecureContextHandle = ( SecureContextHandle_t ) pvPortMalloc( sizeof( SecureContext_t ) );

        if( xSecureContextHandle != NULL )
        {
            /* Allocate the stack space. */
            pucStackMemory = pvPortMalloc( ulSecureStackSize );

            if( pucStackMemory != NULL )
            {
                /* Since stack grows down, the starting point will be the last
                 * location. Note that this location is next to the last
                 * allocated byte because the hardware decrements the stack
                 * pointer before writing i.e. if stack pointer is 0x2, a push
                 * operation will decrement the stack pointer to 0x1 and then
                 * write at 0x1. */
                xSecureContextHandle->pucStackStart = pucStackMemory + ulSecureStackSize;

                /* The stack cannot go beyond this location. This value is
                 * programmed in the PSPLIM register on context switch.*/
                xSecureContextHandle->pucStackLimit = pucStackMemory;

                #if ( configENABLE_MPU == 1 )
                    {
                        /* Store the correct CONTROL value for the task on the stack.
                         * This value is programmed in the CONTROL register on
                         * context switch. */
                        pulCurrentStackPointer = ( uint32_t * ) xSecureContextHandle->pucStackStart;
                        pulCurrentStackPointer--;

                        if( ulIsTaskPrivileged )
                        {
                            *( pulCurrentStackPointer ) = securecontextCONTROL_VALUE_PRIVILEGED;
                        }
                        else
                        {
                            *( pulCurrentStackPointer ) = securecontextCONTROL_VALUE_UNPRIVILEGED;
                        }

                        /* Store the current stack pointer. This value is programmed in
                         * the PSP register on context switch. */
                        xSecureContextHandle->pucCurrentStackPointer = ( uint8_t * ) pulCurrentStackPointer;
                    }
                #else /* configENABLE_MPU */
                    {
                        /* Current SP is set to the starting of the stack. This
                         * value programmed in the PSP register on context switch. */
                        xSecureContextHandle->pucCurrentStackPointer = xSecureContextHandle->pucStackStart;
                    }
                #endif /* configENABLE_MPU */
            }
            else
            {
                /* Free the context to avoid memory leak and make sure to return
                 * NULL to indicate failure. */
                vPortFree( xSecureContextHandle );
                xSecureContextHandle = NULL;
            }
        }
    }

    return xSecureContextHandle;
}
/*-----------------------------------------------------------*/

secureportNON_SECURE_CALLABLE void SecureContext_FreeContext( SecureContextHandle_t xSecureContextHandle )
{
    uint32_t ulIPSR;

    /* Read the Interrupt Program Status Register (IPSR) value. */
    secureportREAD_IPSR( ulIPSR );

    /* Do nothing if the processor is running in the Thread Mode. IPSR is zero
     * when the processor is running in the Thread Mode. */
    if( ulIPSR != 0 )
    {
        /* Ensure that valid parameters are passed. */
        secureportASSERT( xSecureContextHandle != NULL );

        /* Free the stack space. */
        vPortFree( xSecureContextHandle->pucStackLimit );

        /* Free the context itself. */
        vPortFree( xSecureContextHandle );
    }
}
/*-----------------------------------------------------------*/