Exception handling in a data processing apparatus having a secure domain and a less secure domain

A data processing apparatus comprising:

• data processing circuitry for performing data processing operations in response to program code;
• a plurality of registers;
• and
• a data store for storing data, said data store comprising a plurality of regions each region having a secure level, and comprising at least one secure region for storing sensitive data accessible by said data processing circuitry operating in said secure domain and not accessible by said data processing circuitry operating in a less secure domain and a less secure region for storing less secure data;
• said data store comprising at least two stacks a secure stack in said secure region and a less secure stack in said less secure region;
• wherein
• said data processing circuitry comprises exception handling circuitry, said exception handling circuitry being configured to respond to receipt of an exception when said data processing circuitry is executing in said secure domain and said exception indicates switching to executing program code in a less secure domain to clear a set of said registers, said registers within said set of said registers depending on a secure level of said domain of execution and said domain said exception is to be taken in.

A method of processing data on a data processing apparatus, said data processing apparatus comprising processing circuitry for performing data processing operations in response to program code, the processing circuitry comprising exception control circuitry for controlling exception processing, a plurality of registers for storing data, the registers including a first subset of registers and a second subset of registers, and a data store for storing data, the data store comprising a plurality of regions including a secure region and a less secure region, wherein the secure region is for storing data which is accessible by the processing circuitry when operating in a secure domain and not accessible by the processing circuitry when operating in a less secure domain, said method comprising:

• in response to an initial exception from background processing performed by the processing circuitry, employing the exception control circuitry to perform state saving of data from the first subset of registers before triggering the processing circuitry to perform an exception handling routine corresponding to the exception, wherein the exception handling routine has responsibility for performing state saving of data from the second subset of registers;
• and
• in response to a first exception causing a transition from the secure domain to the less secure domain, where the background processing was performed by the processing circuitry in the secure domain, employing the exception control circuitry to perform additional state saving of the data from the second subset of registers before triggering the processing circuitry to perform the exception handling routine in the less secure domain.

A data processing apparatus comprising:

• processing means for performing data processing operations in response to program code, the processing means comprising exception control means for controlling exception processing;
• a plurality of register means for storing data, including a first subset of register means and a second subset of register means;
• and
• data store means for storing data, the data store means comprising a plurality of regions including a secure region and a less secure region, wherein the secure region is for storing data which is accessible by the processing means when operating in a secure domain and not accessible by the processing means when operating in a less secure domain;
• wherein:
• in response to an initial exception from background processing performed by the processing means, the exception control means performs state saving of data from the first subset of register means before triggering the processing means to perform an exception handling routine corresponding to the exception, wherein the exception handling routine has responsibility for performing state saving of data from the second subset of register means;
• and
• in response to a first exception causing a transition from the secure domain to the less secure domain, where the background processing was performed by the processing means in the secure domain, the exception control means performs additional state saving of the data from the second subset of register means before triggering the processing means to perform the exception handling routine in the less secure domain.