Improper Isolation of Shared Resources in Network On Chip

The product does not isolate or incorrectly isolates its on-chip-fabric and internal resources such that they are shared between trusted and untrusted agents, creating timing channels.


Description

Typically, network on chips (NoC) have many internal resources that are shared between packets from different, trust domains. These resources include internal buffers, crossbars and switches, individual ports, and channels. The sharing of resources causes contention and introduces interference between differently trusted domains, which poses a security threat via a timing channel allowing attackers to infer data that belongs to a trusted agent. This may also result in introducing network interference resulting in degraded throughput and latency.

Demonstrations

The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.

Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.

Example One

Consider a NoC that implements a one-dimensional, mesh network with four nodes. This supports two flows: Flow A from node 0 to node 3 (via node 1 and node 2) and Flow B from node 1 to node 2. Flows A and B share a common link between Node 1 and Node 2. Only one flow can use the link in each cycle.

One of the masters to this NoC implements a crypto algorithm (RSA), and another master to the NoC is a core that can be exercised by an attacker. The RSA algorithm performs a modulo multiplication of two, large numbers and depends on each bit of the secret key. The algorithm examines each bit in the secret key and only performs multiplication if the bit is 1. This algorithm is known to be prone to timing attacks. Whenever RSA performs multiplication, there is additional, network traffic to the memory controller. One of the reasons for this is cache conflicts.

Since this is a one-dimensional mesh, only one flow can use the link in each cycle. Also, packets from the attack program and the RSA program share the output port of the network-on-chip. This contention results in network interference, and the throughput and latency of one flow can be affected by the other flow’s demand.

The attacker runs a loop program on the core they control, and this causes a cache miss in every iteration for the RSA algorithm. Thus, by observing network-traffic bandwidth and timing, the attack program can determine when the RSA algorithm is doing a multiply operation (i.e., when secret key bit is 1) and eventually extract the entire, secret key.

Implement priority-based arbitration inside the NoC and have dedicated buffers or virtual channels for routing secret data from trusted agents.

See Also

Peripherals, On-chip Fabric, and Interface/IO Problems

Weaknesses in this category are related to hardware security problems that apply to peripheral devices, IO interfaces, on-chip interconnects, network-o...

Comprehensive CWE Dictionary

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Weaknesses without Software Fault Patterns

CWE identifiers in this view are weaknesses that do not have associated Software Fault Patterns (SFPs), as covered by the CWE-888 view. As such, they represent gaps in...

Weaknesses Introduced During Implementation

This view (slice) lists weaknesses that can be introduced during implementation.


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