Indirect branch predictor security protection

An apparatus, comprising:

• security circuitry configured to provide a first value for an encryption salt value;
• a table comprising circuitry configured to store branch prediction information;
• and
• branch prediction circuitry configured to:
• access a portion of the branch prediction information identified based at least in part on accessing the table using a first index generated by encrypting at least a portion of a program counter corresponding to a branch instruction with the first value for the encryption salt value;
• and
• responsive to the security circuitry changing the encryption salt value to a second value, prevent access of the portion of the branch prediction information based at least in part on an access to the table using a second index generated by encrypting the at least a portion of the program counter corresponding to the branch instruction with the second value for the encryption salt value.

A method comprising:

• performing, by branch prediction circuitry:
• accessing a portion of branch prediction information identified at least in part by accessing a table using a first index generated by encrypting at least a portion of a program counter corresponding to a branch instruction with a first value of an encryption salt value, wherein the table comprises the branch prediction information;
• and
• responsive to security circuitry changing the encryption salt value to a second value, preventing access of the portion of the branch prediction information based at least in part on an access to the table using a second index generated by encrypting the at least a portion of the program counter corresponding to the branch instruction with the second value for the encryption salt value.

A processor comprising:

• instruction fetch circuitry configured to fetch instructions for execution;
• execution circuitry configured to execute instructions fetched by the instruction fetch circuitry;
• security circuitry configured to provide a first value for an encryption salt value;
• a table comprising circuitry configured to store branch prediction information;
• and
• branch prediction circuitry configured to:
• access a portion of the branch prediction information identified based at least in part on accessing the table using a first index generated by encrypting at least a portion of a program counter corresponding to a branch instruction with the first value for the encryption salt value;
• and
• responsive to the security circuitry changing the encryption salt value to a second value, prevent access of the portion of the branch prediction information based at least in part on an access to the table using a second index generated by encrypting the at least a portion of the program counter corresponding to the branch instruction with the second value for the encryption salt value.