Bidirectional trust chaining for trusted boot
A root of trust may include one or more hardware components of an IHS (Information Handling System) that operate using validated hardware instructions. Once a root of trust has been established, it may be extended by validating additional components and the instructions by which these components operate. A chain of trusted boot components may be used to securely initialize a set of components required to support core functions of the IHS. In order to detect components of a trusted boot chain that have been compromised, boot chain components validate their own instructions as well as the instructions to be utilized by the next boot component and the instructions utilized by the prior boot component, thus providing bidirectional validation of trusted boot chain components.
1. A method for validating an ordered sequence of boot components of an Information Handling System (IHS), the method comprising:
retrieving an image of a current boot component of the sequence of boot components, wherein the current boot component follows a prior boot component in the ordered sequence of boot components, and wherein the image comprises hardware instructions for operation of the current boot component, and wherein the image further comprises a digital signature, and wherein the image further comprises a reference hash that is based on the hardware instructions for use by the current boot component and further based on a hash of hardware instructions for use by the prior boot component;
authenticating the digital signature;
calculating a hash based on the hardware instructions that will be used to operate the current boot component and further based on a hash value of hardware instructions in use by for the prior boot component;
comparing the calculated hash and the reference hash to verify an integrity of the hardware instructions that will be used to operate the current boot component and the hardware instructions in use by the prior boot component, wherein a match between the calculated hash and the reference hash confirms the instructions that will be used to operate the current boot component and the instructions in use by the prior boot component have not been compromised; and
initiating validation of a next boot component of the sequence of boot components, wherein the next boot component directly follows the current boot component in the ordered sequence of boot components.
2. The method of claim 1 , wherein the image is stored on a memory device of the IHS during a trusted assembly procedure of the IHS.
3. The method of claim 1 , wherein the digital signature is generated by encrypting the reference hash that is based on the hardware instructions for use by the current boot component and further based on the hash of the hardware instructions for use by the prior boot component.
4. The method of claim 3 , wherein the authentication of the digital signature comprises decrypting the digital signature to recover the reference hash.
5. The method of claim 3 , wherein the image further comprises attributes for configuring the current boot component and wherein the digital signature is further generated based on encrypting the attributes.
6. The method of claim 1 , wherein the image is retrieved based on validated hardware instructions of the prior boot component.
7. The method of claim 1 , further comprising:
retrieving an image of the prior boot component of the sequence of boot components, wherein the image comprises hardware instructions for operation of the prior boot component;
calculating a hash based on the hardware instructions of the prior boot component; and
verifying an integrity of the hardware instructions of the prior boot component based on a comparison of the calculated hash of the prior boot component instructions versus a reference hash of the prior boot component.
8. The method of claim 7 , wherein the image of the current boot component comprises the reference hash of the prior boot component.
9. An Information Handling System (IHS) comprising:
a flash memory; and
an embedded controller coupled to the flash memory, wherein the embedded controller is configured to:
retrieve, from the flash memory, an image of a current boot component of the sequence of boot components, wherein the current boot component follows a prior boot component in the ordered sequence of boot components, and wherein the image comprises hardware instructions for operation of the current boot component, and wherein the image further comprises a digital signature, and wherein the image further comprises a reference hash that is based on the hardware instructions for use by the current boot component and further based on a hash of hardware instructions for use by the prior boot component;
authenticate the digital signature;
calculate a hash based on the hardware instructions that will be used to operate the current boot component and further based on a hash value of hardware instructions in use by the operation of the prior boot component;
compare the calculated hash and the reference hash to verify an integrity of the hardware instructions that will be used to operate the current boot component and the hardware instructions in use by the prior boot component, wherein a match between the calculated hash and the reference hash confirms the instructions that will be used to operate the current boot component and the instructions in use by the prior boot component have not been compromised; and
initiate validation of a next boot component of the sequence of boot components, wherein the next boot component directly follows the current boot component in the ordered sequence of boot components.
10. The IHS of claim 9 , wherein the image is stored in the flash memory during a trusted assembly procedure of the IHS.
11. The IHS of claim 9 , wherein the digital signature is generated by encrypting the reference hash that is based on the hardware instructions for use by the current boot component and further based on the hash of the hardware instructions for use by the prior boot component.
12. The IHS of claim 11 , wherein the authentication of the digital signature comprises decrypting the digital signature to recover the reference hash.
13. The IHS of claim 11 , wherein the image further comprises attributes for configuring the current boot component and wherein the digital signature is further generated based on encrypting the attributes.
14. The IHS of claim 9 , wherein the image is retrieved from the flash memory based on validated hardware instructions of the prior boot component.
15. The IHS of claim 9 , wherein the embedded controller is further configured to:
retrieve an image of the prior boot component of the sequence of boot components, wherein the image comprises hardware instructions for operation of the prior boot component;
calculate a hash based on the hardware instructions of the prior boot component; and
verify an integrity of the hardware instructions of the prior boot component based on a comparison of the calculated hash of the prior boot component instructions versus a reference hash of the prior boot component.
16. An embedded controller coupled to a flash memory of an Information Handling System (IHS), wherein the embedded controller is configured to:
retrieve, from the flash memory, an image of a current boot component of the sequence of boot components, wherein the current boot component follows a prior boot component in the ordered sequence of boot components, and wherein the image comprises hardware instructions for operation of the current boot component, and wherein the image further comprises a digital signature, and wherein the image further comprises a reference hash that is based on the hardware instructions for use by the current boot component and further based on a hash of hardware instructions for use by the prior boot component;
authenticate the digital signature;
calculate a hash based on the hardware instructions that will be used to operate the current boot component and further based on a hash value of hardware instructions in use by the operation of the prior boot component;
compare the calculated hash and the reference hash to verify an integrity of the hardware instructions that will be used to operate the current boot component and the hardware instructions in use by the prior boot component, wherein a match between the calculated hash and the reference hash confirms the instructions that will be used to operate the current boot component and the instructions in use by the prior boot component have not been compromised; and
initiate validation of a next boot component of the sequence of boot components, wherein the next boot component directly follows the current boot component in the ordered sequence of boot components.
17. The embedded controller of claim 16 , wherein the image is stored in the flash memory during a trusted assembly procedure of the IHS.
18. The embedded controller of claim 16 , wherein the digital signature is generated by encrypting the reference hash that is based on the hardware instructions for use by the current boot component and further based on the hash of the hardware instructions for use by the prior boot component, and wherein the authentication of the digital signature comprises decrypting the digital signature to recover the reference hash.
19. The embedded controller of claim 16 , wherein the image is retrieved based on validated hardware instructions of the prior boot component.
20. The embedded controller of claim 16 , wherein the embedded controller is further configured to:
retrieve an image of the prior boot component of the sequence of boot components, wherein the image comprises hardware instructions for operation of the prior boot component;
calculate a hash based on the hardware instructions of the prior boot component; and
verify an integrity of the hardware instructions of the prior boot component based on a comparison of the calculated hash of the prior boot component instructions versus a reference hash of the prior boot component.