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/*
* FreeRTOS Kernel V10.3.0
* 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.
*
* http://www.FreeRTOS.org
* http://aws.amazon.com/freertos
*
* 1 tab == 4 spaces!
*/
/* FreeRTOS includes. */
#include "FreeRTOS.h"
#include "task.h"
/** ARMv7 MPU Details:
*
* - ARMv7 MPU requires that the size of a MPU region is a power of 2.
* - Smallest supported region size is 32 bytes.
* - Start address of a region must be aligned to an integer multiple of the
* region size. For example, if the region size is 4 KB(0x1000), the starting
* address must be N x 0x1000, where N is an integer.
*/
/**
* @brief Size of the shared memory region.
*/
#define SHARED_MEMORY_SIZE 32
/**
* @brief Memory region shared between two tasks.
*/
static uint8_t ucSharedMemory[ SHARED_MEMORY_SIZE ] __attribute__( ( aligned( SHARED_MEMORY_SIZE ) ) );
/**
* @brief Memory region used to track Memory Fault intentionally caused by the
* RO Access task.
*
* RO Access task sets ucROTaskFaultTracker[ 0 ] to 1 before accessing illegal
* memory. Illegal memory access causes Memory Fault and the fault handler
* checks ucROTaskFaultTracker[ 0 ] to see if this is an expected fault. We
* recover gracefully from an expected fault by jumping to the next instruction.
*
* @note We are declaring a region of 32 bytes even though we need only one.
* The reason is that the smallest supported MPU region size is 32 bytes.
*/
static volatile uint8_t ucROTaskFaultTracker[ SHARED_MEMORY_SIZE ] __attribute__( ( aligned( SHARED_MEMORY_SIZE ) ) ) = { 0 };
/*-----------------------------------------------------------*/
/**
* @brief Implements the task which has Read Only access to the memory region
* ucSharedMemory.
*
* @param pvParameters[in] Parameters as passed during task creation.
*/
static void prvROAccessTask( void * pvParameters );
/**
* @brief Implements the task which has Read Write access to the memory region
* ucSharedMemory.
*
* @param pvParameters[in] Parameters as passed during task creation.
*/
static void prvRWAccessTask( void * pvParameters );
/*-----------------------------------------------------------*/
static void prvROAccessTask( void * pvParameters )
{
uint8_t ucVal;
/* Unused parameters. */
( void ) pvParameters;
for( ; ; )
{
/* This task has RO access to ucSharedMemory and therefore it can read
* it but cannot modify it. */
ucVal = ucSharedMemory[ 0 ];
/* Silent compiler warnings about unused variables. */
( void ) ucVal;
/* Since this task has Read Only access to the ucSharedMemory region,
* writing to it results in Memory Fault. Set ucROTaskFaultTracker[ 0 ]
* to 1 to tell the Memory Fault Handler that this is an expected fault.
* The handler will recover from this fault gracefully by jumping to the
* next instruction. */
ucROTaskFaultTracker[ 0 ] = 1;
/* Illegal access to generate Memory Fault. */
ucSharedMemory[ 0 ] = 0;
/* Ensure that the above line did generate MemFault and the fault
* handler did clear the ucROTaskFaultTracker[ 0 ]. */
configASSERT( ucROTaskFaultTracker[ 0 ] == 0 );
#if( configENFORCE_SYSTEM_CALLS_FROM_KERNEL_ONLY == 1 )
{
/* Generate an SVC to raise the privilege. Since privilege
* escalation is only allowed from kernel code, this request must
* get rejected and the task must remain unprivileged. As a result,
* trying to write to ucSharedMemory will still result in Memory
* Fault. */
portRAISE_PRIVILEGE();
/* Set ucROTaskFaultTracker[ 0 ] to 1 to tell the Memory Fault
* Handler that this is an expected fault. The handler will then be
* able to recover from this fault gracefully by jumping to the
* next instruction.*/
ucROTaskFaultTracker[ 0 ] = 1;
/* The following must still result in Memory Fault since the task
* is still running unprivileged. */
ucSharedMemory[ 0 ] = 0;
/* Ensure that the above line did generate MemFault and the fault
* handler did clear the ucROTaskFaultTracker[ 0 ]. */
configASSERT( ucROTaskFaultTracker[ 0 ] == 0 );
}
#else
{
/* Generate an SVC to raise the privilege. Since
* configENFORCE_SYSTEM_CALLS_FROM_KERNEL_ONLY is not enabled, the
* task will be able to escalate privilege. */
portRAISE_PRIVILEGE();
/* At this point, the task is running privileged. The following
* access must not result in Memory Fault. If something goes
* wrong and we do get a fault, the execution will stop in fault
* handler as ucROTaskFaultTracker[ 0 ] is not set (i.e.
* un-expected fault). */
ucSharedMemory[ 0 ] = 0;
/* Lower down the privilege. */
portSWITCH_TO_USER_MODE();
/* Now the task is running unprivileged and therefore an attempt to
* write to ucSharedMemory will result in a Memory Fault. Set
* ucROTaskFaultTracker[ 0 ] to 1 to tell the Memory Fault Handler
* that this is an expected fault. The handler will then be able to
* recover from this fault gracefully by jumping to the next
* instruction.*/
ucROTaskFaultTracker[ 0 ] = 1;
/* The following must result in Memory Fault since the task is now
* running unprivileged. */
ucSharedMemory[ 0 ] = 0;
/* Ensure that the above line did generate MemFault and the fault
* handler did clear the ucROTaskFaultTracker[ 0 ]. */
configASSERT( ucROTaskFaultTracker[ 0 ] == 0 );
}
#endif /* #if( configENFORCE_SYSTEM_CALLS_FROM_KERNEL_ONLY == 1 ) */
/* Wait for a second. */
vTaskDelay( pdMS_TO_TICKS( 1000 ) );
}
}
/*-----------------------------------------------------------*/
static void prvRWAccessTask( void * pvParameters )
{
/* Unused parameters. */
( void ) pvParameters;
for( ; ; )
{
/* This task has RW access to ucSharedMemory and therefore can write to
* it. */
ucSharedMemory[ 0 ] = 0;
/* Wait for a second. */
vTaskDelay( pdMS_TO_TICKS( 1000 ) );
}
}
/*-----------------------------------------------------------*/
void vStartMPUDemo( void )
{
/**
* Since stack of a task is protected using MPU, it must satisfy MPU
* requirements as mentioned at the top of this file.
*/
static StackType_t xROAccessTaskStack[ configMINIMAL_STACK_SIZE ] __attribute__( ( aligned( configMINIMAL_STACK_SIZE * sizeof( StackType_t ) ) ) );
static StackType_t xRWAccessTaskStack[ configMINIMAL_STACK_SIZE ] __attribute__( ( aligned( configMINIMAL_STACK_SIZE * sizeof( StackType_t ) ) ) );
TaskParameters_t xROAccessTaskParameters =
{
.pvTaskCode = prvROAccessTask,
.pcName = "ROAccess",
.usStackDepth = configMINIMAL_STACK_SIZE,
.pvParameters = NULL,
.uxPriority = tskIDLE_PRIORITY,
.puxStackBuffer = xROAccessTaskStack,
.xRegions = {
{ ucSharedMemory, SHARED_MEMORY_SIZE, portMPU_REGION_PRIVILEGED_READ_WRITE_UNPRIV_READ_ONLY | portMPU_REGION_EXECUTE_NEVER },
{ ( void * ) ucROTaskFaultTracker, SHARED_MEMORY_SIZE, portMPU_REGION_READ_WRITE | portMPU_REGION_EXECUTE_NEVER },
{ 0, 0, 0 },
}
};
TaskParameters_t xRWAccessTaskParameters =
{
.pvTaskCode = prvRWAccessTask,
.pcName = "RWAccess",
.usStackDepth = configMINIMAL_STACK_SIZE,
.pvParameters = NULL,
.uxPriority = tskIDLE_PRIORITY,
.puxStackBuffer = xRWAccessTaskStack,
.xRegions = {
{ ucSharedMemory, SHARED_MEMORY_SIZE, portMPU_REGION_READ_WRITE | portMPU_REGION_EXECUTE_NEVER},
{ 0, 0, 0 },
{ 0, 0, 0 },
}
};
/* Create an unprivileged task with RO access to ucSharedMemory. */
xTaskCreateRestricted( &( xROAccessTaskParameters ), NULL );
/* Create an unprivileged task with RW access to ucSharedMemory. */
xTaskCreateRestricted( &( xRWAccessTaskParameters ), NULL );
}
/*-----------------------------------------------------------*/
portDONT_DISCARD void vHandleMemoryFault( uint32_t * pulFaultStackAddress )
{
uint32_t ulPC;
uint16_t usOffendingInstruction;
/* Is this an expected fault? */
if( ucROTaskFaultTracker[ 0 ] == 1 )
{
/* Read program counter. */
ulPC = pulFaultStackAddress[ 6 ];
/* Read the offending instruction. */
usOffendingInstruction = *( uint16_t * )ulPC;
/* From ARM docs:
* If the value of bits[15:11] of the halfword being decoded is one of
* the following, the halfword is the first halfword of a 32-bit
* instruction:
* - 0b11101.
* - 0b11110.
* - 0b11111.
* Otherwise, the halfword is a 16-bit instruction.
*/
/* Extract bits[15:11] of the offending instruction. */
usOffendingInstruction = usOffendingInstruction & 0xF800;
usOffendingInstruction = ( usOffendingInstruction >> 11 );
/* Determine if the offending instruction is a 32-bit instruction or
* a 16-bit instruction. */
if( usOffendingInstruction == 0x001F ||
usOffendingInstruction == 0x001E ||
usOffendingInstruction == 0x001D )
{
/* Since the offending instruction is a 32-bit instruction,
* increment the program counter by 4 to move to the next
* instruction. */
ulPC += 4;
}
else
{
/* Since the offending instruction is a 16-bit instruction,
* increment the program counter by 2 to move to the next
* instruction. */
ulPC += 2;
}
/* Save the new program counter on the stack. */
pulFaultStackAddress[ 6 ] = ulPC;
/* Mark the fault as handled. */
ucROTaskFaultTracker[ 0 ] = 0;
}
else
{
/* This is an unexpected fault - loop forever. */
for( ; ; )
{
}
}
}
/*-----------------------------------------------------------*/
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