In today's post, we will discuss a critical vulnerability that has been discovered in the Arithmetic Logic Unit (ALU) of the OpenRISC mor1kx processor. CVE-2021-41612 is a highly concerning issue, as it directly affects the carry flag - potentially leading to corruption in the execution of software reliant on this flag. Due to the severity of this vulnerability, software developers and hardware producers should take care to apply patches and remediations as soon as possible. We will dive into the details, covering the exploit, relevant code snippets, and links to original sources.

Description of Vulnerability

The vulnerability, assigned to CVE-2021-41612, was discovered within the ALU unit of the OpenRISC mor1kx processor. The critical issue concerns the improper updating of the carry flag during the subtraction operation. As a result, the carry flag contains incorrect values leading to possible corruption of software execution. With the increasing reliance on embedded systems and IoT applications, the potential negative impact on the affected devices cannot be understated.

One way to illustrate the erroneous behavior in the processor is shown in this code snippet

or32-asm
l.addi   r3,r,xFFFF ; Set r3 to xFFFF
l.addi   r4,r,x0001 ; Set r4 to x0001
l.sub    r5,r3,r4     ; Subtract r4 from r3, store result in r5
l.sfne  r5,r5,xFFFE  ; The result r5 should be xFFFE, but it's not!

In this example, we attempt to execute subtraction using the l.sub instruction. However, the incorrect carry flag value generated by the subtraction operation causes the comparison result using l.sfne to fail.

Exploit Details

The consequences of an incorrect carry flag can be severe, especially if the affected software relies on the carry flag for crucial tasks such as data processing, control loops, or even security checks. Exploiting this vulnerability could allow an attacker to manipulate these processes, resulting in unpredictable and potentially harmful behavior in the affected system.

Since the OpenRISC mor1kx processor is employed in a wide range of applications, including but not limited to: IoT devices, embedded systems, industrial automation, and robotics, this vulnerability warrants serious attention and swift action.

Original References

For a comprehensive understanding of the issue and its implications, we recommend reviewing the following original resources:

1. GitHub repository for OpenRISC mor1kx processor: https://github.com/openrisc/mor1kx

2. Vulnerability report on Mitre.org: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-41612

3. National Vulnerability Database entry: https://nvd.nist.gov/vuln/detail/CVE-2021-41612

Conclusion

CVE-2021-41612 proves to be a significant vulnerability for developers and hardware manufacturers utilizing the OpenRISC mor1kx processor. The issue in the ALU unit might lead to severe consequences if not identified and patched promptly. The primary concern is potential corruption in the execution of software dependent on the correct value of the carry flag, which may result in a wide range of adverse effects.

To address and remediate CVE-2021-41612, stakeholders are strongly recommended to follow the advice provided in the original sources and ensure they apply the necessary patches. This not only demonstrates responsible handling of the vulnerability but also serves as a reminder of the importance of being diligent in developing and using complex hardware components.

Timeline

Published on: 04/18/2023 12:15:00 UTC
Last modified on: 04/27/2023 19:46:00 UTC