FUSE-ENABLED SECURE BIOS MECHANISM WITH OVERRIDE FEATURE

摘要

An apparatus is provided for protecting a basic input/output system (BIOS) in a computing system. The apparatus includes a BIOS read only memory (ROM), a tamper detector, a random number generator, a JTAG control chain, a fuse, a machine specific register, and an access controller. The BIOS ROM includes BIOS contents stored as plaintext, and an encrypted message digest, where the encrypted message digest has an encrypted version of a first message digest that corresponds to the BIOS contents. The tamper detector is operatively coupled to the BIOS ROM, and is configured to generate a BIOS check interrupt at a combination of prescribed intervals and event occurrences, and is configured to access the BIOS contents and the encrypted message digest upon assertion of the BIOS check interrupt, and is configured to direct a microprocessor to generate a second message digest corresponding to the BIOS contents and a decrypted message digest corresponding to the encrypted message digest, and is configured to compare the second message digest with the decrypted message digest, and is configured to preclude the operation of the microprocessor if the second message digest and the decrypted message digest are not equal. The random number generator disposed within the microprocessor, and generates a random number at completion of a current BIOS check, which is employed to set a following prescribed interval, whereby the prescribed intervals are randomly varied. The JTAG control chain is configured to program the combination of prescribed intervals and event occurrences within tamper detection microcode storage. The fuse is configured to indicate whether programming of the combination of prescribed intervals and event occurrences is to be disabled. The machine specific register is configured to store a value therein. The access control element is coupled to the fuse, the machine specific register, and the JTAG control chain, and is configured to determine that the fuse is blown, and configured to direct the JTAG control chain to enable programming of the combination of prescribed intervals and event occurrences if the value matches an override value within the access control element during a period that the value is stored within the machine specific register.

主权项

1. An apparatus for protecting a basic input/output system (BIOS) in a computing system, the apparatus comprising:
a BIOS read only memory (ROM), comprising:
BIOS contents, wherein said BIOS contents are stored as plaintext; andan encrypted message digest, wherein said encrypted message digest comprises an encrypted version of a first message digest that corresponds to said BIOS contents; a tamper detector, operatively coupled to said BIOS ROM, configured to generate a BIOS check interrupt at a combination of prescribed intervals and event occurrences, and configured to access said BIOS contents and said encrypted message digest upon assertion of said BIOS check interrupt, and configured to direct a microprocessor to generate a second message digest corresponding to said BIOS contents and a decrypted message digest corresponding to said encrypted message digest, and configured to compare said second message digest with said decrypted message digest, and configured to preclude said operation of said microprocessor if said second message digest and said decrypted message digest are not equal; a random number generator disposed within said microprocessor, wherein said random number generator generates a random number at completion of a current BIOS check, which is employed to set a following prescribed interval, whereby said prescribed intervals are randomly varied; a JTAG control chain, configured to program said combination of prescribed intervals and event occurrences within tamper detection microcode storage; a fuse, configured to indicate whether programming of said combination of prescribed intervals and event occurrences is to be disabled; a machine specific register, configured to store a value therein; and an access control element, coupled to said fuse, said machine specific register, and said JTAG control chain, configured to determine that said fuse is blown, and configured to direct said JTAG control chain to enable programming of said combination of prescribed intervals and event occurrences if said value matches an override value within said access control element during a period that said value is stored within said machine specific register.