摘要:
A fetch unit (a) fetches a block of instruction data from an instruction cache of the microprocessor; (b) performs an XOR on the block with a data entity to generate plain text instruction data; and (c) provides the plain text instruction data to an instruction decode unit. In a first instance the block comprises encrypted instruction data and the data entity is a decryption key. In a second instance the block comprises unencrypted instruction data and the data entity is Boolean zeroes. The time required to perform (a), (b), and (c) is the same in the first and second instances regardless of whether the block is encrypted or unencrypted. A decryption key generator selects first and second keys from a plurality of keys, rotates the first key, and adds/subtracts the rotated first key to/from the second key, all based on portions of the fetch address, to generate the decryption key.
摘要:
A fetch unit fetches a sequence of blocks of encrypted instructions of an encrypted program from an instruction cache at a corresponding sequence of fetch address values. While fetching each block of the sequence, the fetch unit generates a decryption key as a function of key values and the corresponding fetch address value, and decrypts the encrypted instructions using the generated decryption key by XORing them together. A switch key instruction instructs the microprocessor to update the key values in the fetch unit while the fetch unit is fetching the sequence of blocks. The fetch unit inherently provides an effective decryption key length that depends upon the function and amount of key values used. Including one or more switch key instructions within the encrypted program increases the effective decryption key length up to the encrypted program length.
摘要:
A fetch unit (a) fetches a block of instruction data from an instruction cache of the microprocessor; (b) performs an XOR on the block with a data entity to generate plain text instruction data; and (c) provides the plain text instruction data to an instruction decode unit. In a first instance the block comprises encrypted instruction data and the data entity is a decryption key. In a second instance the block comprises unencrypted instruction data and the data entity is Boolean zeroes. The time required to perform (a), (b), and (c) is the same in the first and second instances regardless of whether the block is encrypted or unencrypted. A decryption key generator selects first and second keys from a plurality of keys, rotates the first key, and adds/subtracts the rotated first key to/from the second key, all based on portions of the fetch address, to generate the decryption key.
摘要:
A branch target address cache (BTAC) caches history information associated with branch and switch key instructions previously executed by a microprocessor. The history information includes a target address and an identifier (index into a register file) for identifying key values associated with each of the previous branch and switch key instructions. A fetch unit receives from the BTAC a prediction that the fetch unit fetched a previous branch and switch key instruction and receives the target address and identifier associated with the fetched branch and switch key instruction. The fetch unit also fetches encrypted instruction data at the associated target address and decrypts (via XOR) the fetched encrypted instruction data based on the key values identified by the identifier, in response to receiving the prediction. If the BTAC predicts correctly, a pipeline flush normally associated with the branch and switch key instruction is avoided.
摘要:
A microprocessor includes a storage element having a plurality of locations each storing decryption key data associated with an encrypted program. A control register field (may be x86 EFLAGS register reserved field) specifies a storage element location associated with a currently executing encrypted program. The microprocessor restores from memory to the control register a previously saved value of the field in response to executing a return from interrupt instruction. A fetch unit fetches encrypted instructions of the currently executing encrypted program and decrypts them using the decryption key data stored the storage element location specified by the restored field value. A kill bit associated with each storage element location may be employed if the location is clobbered because more encrypted programs are multitasked than available locations in the storage element, in which case an exception is generated to re-load the clobbered decryption key data in response to the return from interrupt instruction.
摘要:
A microprocessor includes a storage element having a plurality of locations each storing decryption key data associated with an encrypted program. A control register field (may be x86 EFLAGS register reserved field) specifies a storage element location associated with a currently executing encrypted program. The microprocessor restores from memory to the control register a previously saved value of the field in response to executing a return from interrupt instruction. A fetch unit fetches encrypted instructions of the currently executing encrypted program and decrypts them using the decryption key data stored the storage element location specified by the restored field value. A kill bit associated with each storage element location may be employed if the location is clobbered because more encrypted programs are multitasked than available locations in the storage element, in which case an exception is generated to re-load the clobbered decryption key data in response to the return from interrupt instruction.
摘要:
A microprocessor includes an architected register having a bit (may be x86 EFLAGS register reserved bit) set by the microprocessor. A fetch unit fetches encrypted instructions from an instruction cache and decrypts them (via XOR) prior to executing them, in response to the microprocessor setting the bit. The microprocessor saves the bit value to a stack in memory and then clears the bit in response to receiving an interrupt. The fetch unit fetches unencrypted instructions from the instruction cache and executes them without decrypting them after the microprocessor clears the bit. The microprocessor restores the saved value from the stack in memory to the bit in the architected register (and in one embodiment, also restores decryption key values) in response to executing a return from interrupt instruction. The fetch unit resumes fetching and decrypting the encrypted instructions in response to determining that the restored value of the bit is set.
摘要:
A microprocessor includes a fetch unit that fetches and decrypts an (atomic) branch and switch key instruction using first decryption key data. If the branch direction is not taken, the fetch unit fetches and decrypts the next sequential instruction after the branch and switch key instruction using the first decryption key data. If the direction is taken, the fetch unit fetches and decrypts a target instruction of the branch and switch key instruction using second decryption key data that is different from the first decryption key data. The instruction points to the decryption key data; alternatively, the microprocessor consults a mapping of target address ranges to decryption key data. An encryption program replaces conventional inter-program-chunk branch instructions with branch and switch key instructions before encrypting the program using information that divides the program into a sequence of chunks each chunk being a sequence of instructions and having distinct associated encryption key data.
摘要:
A branch target address cache (BTAC) caches history information associated with branch and switch key instructions previously executed by a microprocessor. The history information includes a target address and an identifier (index into a register file) for identifying key values associated with each of the previous branch and switch key instructions. A fetch unit receives from the BTAC a prediction that the fetch unit fetched a previous branch and switch key instruction and receives the target address and identifier associated with the fetched branch and switch key instruction. The fetch unit also fetches encrypted instruction data at the associated target address and decrypts (via XOR) the fetched encrypted instruction data based on the key values identified by the identifier, in response to receiving the prediction. If the BTAC predicts correctly, a pipeline flush normally associated with the branch and switch key instruction is avoided.
摘要:
A microprocessor includes a storage element that stores decryption key data and a fetch unit that fetches and decrypts program instructions using a value of the decryption key data stored in the storage element. The fetch unit fetches an instance of a branch and switch key instruction and decrypts it using a first value of the decryption key data stored in the storage element. If the branch is taken, the microprocessor loads the storage element with a second value of the decryption key data for subsequent use by the fetch unit to decrypt an instruction fetched at a target address specified by the branch and switch key instruction. If the branch is not taken, the microprocessor retains the first value of the decryption key data in the storage element for subsequent use by the fetch unit to decrypt an instruction sequentially following the branch and switch key instruction.