Stack pointer switch validity checking

A method comprising:

• performing a stack pointer switch validity checking operation associated with a switch of a stack pointer from an outgoing stack pointer value to an incoming stack pointer value, the stack pointer switch validity checking operation comprising verifying whether an incoming data value obtained by memory access circuitry in response to a memory access request specifying an address determined based on the incoming stack pointer value meets at least one stack cap value validity condition, the at least one stack cap value validity condition including a condition that a predetermined portion of the incoming data value corresponds to a given page address indicative of a page of address space comprising the address determined based on the incoming stack pointer value, in which:
• whether the incoming data value meets the at least one stack cap value validity condition is determined independent of whether a further portion of the incoming data value other than the predetermined portion corresponds to sub-page address bits of the address determined based on the incoming stack pointer value;
• and
• the method comprises triggering an error handling response in response to determining that the incoming data value fails to meet the at least one stack cap value validity condition.

A non-transitory storage medium storing a computer program comprising instructions which, when executed by a host data processing apparatus, control the host data processing apparatus to provide an instruction execution environment for executing target code, the computer program comprising:

• memory access program logic to perform a stack access to a stack data structure based on a stack pointer;
• and
• processing program logic to perform a stack pointer switch validity checking operation associated with a switch of the stack pointer from an outgoing stack pointer value to an incoming stack pointer value, the stack pointer switch validity checking operation comprising verifying whether an incoming data value obtained by the memory access program logic in response to a request specifying an address determined based on the incoming stack pointer value meets at least one stack cap value validity condition, the at least one stack cap value validity condition including a condition that a predetermined portion of the incoming data value corresponds to a given page address indicative of a page of address space comprising the address determined based on the incoming stack pointer value, in which:
• the processing program logic is configured to determine whether the incoming data value meets the at least one stack cap value validity condition, independent of whether a further portion of the incoming data value other than the predetermined portion corresponds to sub-page address bits of the address determined based on the incoming stack pointer value;
• and
• the processing program logic is configured to trigger an error handling response in response to determining that the incoming data value fails to meet the at least one stack cap value validity condition.