The product uses an obsolete encoding mechanism to implement access controls.

Within a System-On-a-Chip (SoC), various circuits and hardware engines generate transactions for the purpose of accessing (read/write) assets or performing various actions (e.g., reset, fetch, compute, etc.). Among various types of message information, a typical transaction is comprised of source identity (identifying the originator of the transaction) and a destination identity (routing the transaction to the respective entity). Sometimes the transactions are qualified with a Security Token. This Security Token helps the destination agent decide on the set of allowed actions (e.g., access to an asset for reads and writes). A policy encoder is used to map the bus transactions to Security Tokens that in turn are used as access-controls/protection mechanisms. A common weakness involves using an encoding which is no longer trusted, i.e., an obsolete encoding.

This listing shows possible areas for which the given weakness could appear. These may be for specific named Languages, Operating Systems, Architectures, Paradigms, Technologies, or a class of such platforms. The platform is listed along with how frequently the given weakness appears for that instance.

Languages	Class: Not Language-Specific (Undetermined Prevalence)
Operating Systems	Class: Not OS-Specific (Undetermined Prevalence)
Architectures	Class: Not Architecture-Specific (Undetermined Prevalence)
Technologies	Class: Not Technology-Specific (Undetermined Prevalence)

Example 1

For example, consider a system that has four bus masters. The table below provides bus masters, their Security Tokens, and trust assumptions.

Bus Master	Security Token Decoding	Trust Assumptions
Master_0	"00"	Untrusted
Master_1	"01"	Trusted
Master_2	"10"	Untrusted
Master_3	"11"	Untrusted

The policy encoding is to be defined such that Security Token will be used in implemented access-controls. The bits in the bus transaction that contain Security-Token information are Bus_transaction [15:11]. The assets are the AES-Key registers for encryption or decryption. The key of 128 bits is implemented as a set of four, 32-bit registers.

Register	Field description
AES_ENC_DEC_KEY_0	AES key [0:31] for encryption or decryption, Default 0x00000000
AES_ENC_DEC_KEY_1	AES key [32:63] for encryption or decryption, Default 0x00000000
AES_ENC_DEC_KEY_2	AES key [64:95] for encryption or decryption, Default 0x00000000
AES_ENC_DEC_KEY_4	AES key [96:127] for encryption or decryption, Default 0x00000000

Below is an example of a policy encoding scheme inherited from a previous project where all "ODD" numbered Security Tokens are trusted.

The inherited policy encoding is obsolete and does not work for the new system where an untrusted bus master with an odd Security Token exists in the system, i.e., Master_3 whose Security Token is "11". Based on the old policy, the untrusted bus master (Master_3) has access to the AES-Key registers. To resolve this, a register AES_KEY_ACCESS_POLICY can be defined to provide necessary, access controls:

New Policy:

AES_KEY_ACCESS_POLICY

[31:0] Default 0x00000002 - agent with Security Token "1" has access to AES_ENC_DEC_KEY_0 through AES_ENC_DEC_KEY_4 registers

The AES_KEY_ACCESS_POLICY register defines which agents with a Security Token in the transaction can access the AES-key registers. Each bit in this 32-bit register defines a Security Token. There could be a maximum of 32 security Tokens that are allowed access to the AES-key registers. The number of the bit when set (i.e., "1") allows respective action from an agent whose identity matches the number of the bit and, if "0" (i.e., Clear), disallows the respective action to that corresponding agent. Thus, any bus master with Security Token "01" is allowed access to the AES-Key registers. Below is the Pseudo Code for policy encoding:

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