理解与应用mpu用户模式

（MPU_RASR）配置成某一个值，在特权(Privilegedpermissions)和用户模式(Unprivilegedpermissions)的访问许可是不同解这些名词，并讨论在STM32MCU代码中如何使用内存保护单元MPU的特权与用户模式。MPU(MemoryProtection用来设置内存属性的MPU_RASR寄存器字段描述如下：位26:数据访问许可(RO,RW或者无权限21:SCB155AP[2MPU（MPU_RASR）配置成某一个值，在特权(Privilegedpermissions)和用户模式(Unprivilegedpermissions)的访问许可是不同STM32MCUMPU的特权与用户模式。MPU(MemoryProtectionSRAM区域定义成不可执行，来阻止代码注入型攻击。也可以用来改变内存的性质，例如是否允许缓存(Cache)。MPU_RASR寄存器字段描述如下：位26:数据访问许可(RO,RW或者无权限21:SCB155AP[2代码拥有所有的访问许可；而代码运行在用户模式，则访问权限受限制。限制包括在系统设计阶段就定义的可运行指令限制，PU3开发板：STM32L476RGAP[2CorexPUPU代码拥有所有的访问许可；而代码运行在用户模式，则访问权限受限制。限制包括在系统设计阶段就定义的可运行指令限制，PU单元动态所定义的内存访问规则。图表3在代码中结合特权与用户模式使用开发板：STM32L476RGAP[2，和复制CORTEXM_MPU\Src\stm32_mpu.c到CORTEXM_ModePrivilege\Src目录下STM32CubeSTM32Cube_FW_L4_V1.6.0可以发现，固件库已分别实现了特权模式与用户模式的切换（CORTEXM_ModePrivilege）MPU的配置（CORTEXM_MPU）。STM32MPU功能。CORTEXM_MPU\Src\stm32_mpu.cCORTEXM_ModePrivilege\Src目录下在IAR下只需添加C文件。/*/*#include#include"stm32_mpu.h"/**@addtogroup*/**@addtogroup*/*GettheThreadmodestackused*/if((/*GettheThreadmodestackused*/if((get_CONTROL()&0x02)==SP_MAIN){/*Mainstackisusedasthecurrentstack*/CurrentStack=SP_MAIN;}{/*Processstackisusedasthecurrentstack*/CurrentStack=SP_PROCESS;/*Getprocessstackpointervalue*/PSPValue=get_PSP();}MPU_Config();/*added*/CORTEXM_ModePrivilegestm32_mpu.cstm32_mpu.h添加到工程文件中。IARKeil略有不同，IARC文件。/*/*#include#include"stm32_mpu.h"/**@addtogroup*/**@addtogroup*/*/*GettheThreadmodestackused*/if((get_CONTROL()&0x02)==SP_MAIN){/*Mainstackisusedasthecurrentstack*/CurrentStack=SP_MAIN;}{/*Processstackisusedasthecurrentstack*/CurrentStack=SP_PROCESS;/*Getprocessstackpointervalue*/PSPValue=get_PSP();}MPU_Config();/*added*/MPU_AccessPermConfig();/*added*/voidvoid{/*ConfigureregionforPrivilegedReadOnlyArrayasREGIONN?,32byteandRonlyinprivilegedmode*//*DisableMPU*/voidvoid{/*ConfigureregionforPrivilegedReadOnlyArrayasREGIONN?,32byteandRonlyinprivilegedmode*//*DisableMPU*/MPU_InitStruct.Enable=MPU_REGION_ENABLE;MPU_InitStruct.BaseAddressMPU_InitStruct.Enable=MPU_REGION_ENABLE;MPU_InitStruct.BaseAddress=ARRAY_ADDRESS_START;MPU_InitStruct.Size=ARRAY_SIZE;MPU_InitStruct.AccessPermission=portMPU_REGION_PRIVILEGED_READ_WRITE;MPU_InitStruct.IsBufferable=MPU_ACCESS_NOT_BUFFERABLE;MPU_InitStruct.IsCacheable=MPU_ACCESS_NOT_CACHEABLE;MPU_InitStruct.IsShareable=MPU_ACCESS_NOT_SHAREABLE;MPU_InitStruct.Number=ARRAY_REGION_NUMBER;MPU_InitStruct.TypeExtField=MPU_TEX_LEVEL0;MPU_InitStruct.SubRegionDisable=0x00;MPU_InitStruct.DisableExec=MPU_INSTRUCTION_ACCESS_ENABLE;/*EnableMPU(anyaccessnotcoveredbyanyenabledregionwillcauseafault)*//*ReadfromPrivilegedReadOnlyArray.Thiswillnotgenerateerror*/{PrivilegedReadOnlyArray[0]=}/*UncommentthefollowinglinetowritetoPrivilegedReadOnlyArray.Thiswillgenerateerror*/PrivilegedReadOnlyArray[0]=}/*Switch/*SwitchThreadmodefromprivilegedto /*Threadmodehasunprivilegedaccessset_CONTROL(THREAD_MODE_UNPRIVILEGED|/*ExecuteISBinstructiontoflushpipelineasrecommendedbyArm/*UnprivilegedaccessmainlyaffectabilityUseornotusecertaininstructionssuchasMSRAccessSystemControlSpace(SCS)registerssuchasNVICandSysTick/*CheckThreadmodeprivilegestatusif((get_CONTROL()&0x01)=={/*Threadmodehasprivilegedaccess*/ThreadMode=THREAD_MODE_PRIVILEGED;}{MPU_InitStruct.Enable=MPU_REGION_ENABLE;MPU_InitStruct.BaseAddressMPU_InitStruct.Enable=MPU_REGION_ENABLE;MPU_InitStruct.BaseAddress=ARRAY_ADDRESS_START;MPU_InitStruct.Size=ARRAY_SIZE;MPU_InitStruct.AccessPermission=portMPU_REGION_PRIVILEGED_READ_WRITE;MPU_InitStruct.IsBufferable=MPU_ACCESS_NOT_BUFFERABLE;MPU_InitStruct.IsCacheable=MPU_ACCESS_NOT_CACHEABLE;MPU_InitStruct.IsShareable=MPU_ACCESS_NOT_SHAREABLE;MPU_InitStruct.Number=ARRAY_REGION_NUMBER;MPU_InitStruct.TypeExtField=MPU_TEX_LEVEL0;MPU_InitStruct.SubRegionDisable=0x00;MPU_InitStruct.DisableExec=MPU_INSTRUCTION_ACCESS_ENABLE;/*EnableMPU(anyaccessnotcoveredbyanyenabledregionwillcauseafault)*//*ReadfromPrivilegedReadOnlyArray.Thiswillnotgenerateerror*/{PrivilegedReadOnlyArray[0]=}/*UncommentthefollowinglinetowritetoPrivilegedReadOnlyArray.Thiswillgenerateerror*/PrivilegedReadOnlyArray[0]=}/*Switch/*SwitchThreadmodefromprivilegedto /*Threadmodehasunprivilegedaccessset_CONTROL(THREAD_MODE_UNPRIVILEGED|/*ExecuteISBinstructiontoflushpipelineasrecommendedbyArm/*UnprivilegedaccessmainlyaffectabilityUseornotusecertaininstructionssuchasMSRAccessSystemControlSpace(SCS)registerssuchasNVICandSysTick/*CheckThreadmodeprivilegestatusif((get_CONTROL()&0x01)=={/*Threadmodehasprivilegedaccess*/ThreadMode=THREAD_MODE_PRIVILEGED;}{/*/*Threadmodehasunprivilegedaccess*/ThreadMode=THREAD_MODE_UNPRIVILEGED;}{PrivilegedReadOnlyArray[0]=}PrivilegedReadOnlyArray[0]=/*/*SwitchThreadmodefromprivilegedto /*Threadmodehasunprivilegedaccessset_CONTROL(THREAD_MODE_UNPRIVILEGED|/*/*Generateasystemcallexception,andintheISRswitchbackThreadmodetoprivileged*/@briefThisfunctionhandlesSVCall@param@retvalvoid{/*SwitchbackThreadmodetoprivilegedset_CONTROL(THREAD_MODE_PRIVILEGED|/*ExecuteISBinstructiontoflushpipelineasrecommendedbyArm}@briefThisfunctionhandlesMemoryManage@param@retvalvoid{/*GotoinfiniteloopwhenMemoryManageexceptionoccurs*/while(1)/*/*Threadmodehasunprivilegedaccess*/ThreadMode=THREAD_MODE_UNPRIVILEGED;}{PrivilegedReadOnlyArray[0]=}PrivilegedReadOnlyArray[0]=/*/*SwitchThreadmodefromprivilegedto /*Threadmodehasunprivilegedaccessset_CONTROL(THREAD_MODE_UNPRIVILEGED|/*/*Generateasystemcallexception,andintheISRswitchbackThreadmodetoprivileged*/@briefThisfunct