CWE-1298: Hardware Logic Contains Race Conditions

What is Hardware Logic Contains Race Conditions?

• Overview: A race condition in hardware logic occurs when signals take different times to reach a logic gate, potentially causing errors and security issues if the hardware doesn't behave as expected.

• Exploitation Methods:

• Attackers can exploit these timing errors to cause logic circuits to behave in unintended ways.
• Common attack patterns include timing attacks and glitching, where the goal is to force the system into an insecure state.

• Security Impact:

• Direct consequences of successful exploitation include unauthorized access or control over hardware functions.
• Potential cascading effects could lead to broader system failures or vulnerabilities being exposed.
• Business impact may involve data breaches, loss of customer trust, and financial loss due to system downtime or repairs.

• Prevention Guidelines:

• Specific code-level fixes involve using synchronous design techniques to ensure signal timing is consistent.
• Security best practices include thorough testing and validation of all hardware logic designs for timing errors.
• Recommended tools and frameworks involve using formal verification tools and hardware description language (HDL) simulators to detect and mitigate race conditions.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Verilog, VHDL

Affected Technologies: System on Chip

Vulnerable Code Example

// This Verilog module for a simple ALU (Arithmetic Logic Unit) contains a race condition.
// The operations are controlled by the `op` signal, but there's no synchronization mechanism
// to ensure that `op` is stable before it affects the output. This can lead to inconsistent results.

module ALU (
    input [1:0] op,     // Operation selector
    input [7:0] A, B,   // Operands
    output reg [7:0] Y  // Output result
);
    always @(A, B, op) begin
        case (op) // Race condition due to lack of synchronization
            2'b00: Y = A + B;
            2'b01: Y = A - B;
            2'b10: Y = A & B;
            2'b11: Y = A | B;
        endcase
    end
endmodule

Explanation

In this vulnerable example, the ALU operations are directly dependent on the op signal, which can change asynchronously with respect to the operands A and B. This lack of synchronization can lead to race conditions where the output Y may be computed with an unstable or intermediate value of op, resulting in incorrect or inconsistent outputs.

How to fix Hardware Logic Contains Race Conditions?

Fixed Code Example

// Fixed code with comments explaining the security controls implemented.

module ALU (
    input clk,                // Clock signal for synchronization
    input [1:0] op,           // Operation selector
    input [7:0] A, B,         // Operands
    output reg [7:0] Y        // Output result
);
    reg [1:0] op_reg;         // Register to hold the stable operation code

    always @(posedge clk) begin // Synchronize operation selection with clock
        op_reg <= op;            // Store the operation code on clock edge
    end

    always @(posedge clk) begin // Ensure operations happen on clock edge
        case (op_reg)
            2'b00: Y <= A + B;
            2'b01: Y <= A - B;
            2'b10: Y <= A & B;
            2'b11: Y <= A | B;
        endcase
    end
endmodule

Explanation

In the fixed example, the op signal is synchronized with a clock signal by storing it in a register op_reg on the positive edge of the clock. This ensures that any changes to op are captured and stabilized before being used in the ALU operations. The operations themselves are also synchronized with the clock, ensuring that the output Y is updated only after the op signal is stable. This approach eliminates race conditions by making sure that all operations are synchronized with the clock, enhancing the reliability and security of the hardware design.