CVE-2021-28690 in Xen
Summary
by MITRE • 06/29/2021
x86: TSX Async Abort protections not restored after S3 This issue relates to the TSX Async Abort speculative security vulnerability. Please see https://xenbits.xen.org/xsa/advisory-305.html for details. Mitigating TAA by disabling TSX (the default and preferred option) requires selecting a non-default setting in MSR_TSX_CTRL. This setting isn't restored after S3 suspend.
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Analysis
by VulDB Data Team • 07/03/2021
The vulnerability described in CVE-2021-28690 represents a critical security flaw in x86 processor implementations that affects systems utilizing the TSX Async Abort (TAA) mitigation mechanisms. This issue specifically impacts systems where the TSX Async Abort protections are not properly restored after system suspend-to-RAM operations, creating a persistent security gap that can be exploited by malicious actors. The vulnerability stems from the improper handling of the MSR_TSX_CTRL register during system power state transitions, particularly when transitioning from the suspend-to-RAM (S3) state back to active operation. The TAA vulnerability itself is a speculative execution flaw that allows attackers to potentially extract sensitive information from processor caches through asynchronous transactional memory aborts, making it a significant concern for systems handling confidential data.
The technical flaw manifests in the failure of the operating system or hypervisor to restore the proper TSX_CTRL register settings after a system resume from S3 suspend state. When systems disable TSX as a mitigation against TAA vulnerabilities, they typically configure the MSR_TSX_CTRL register to prevent speculative execution of TSX instructions. However, during the S3 suspend-resume cycle, this critical configuration is not properly restored, leaving the system vulnerable to TAA attacks even after the system appears to be fully operational. This behavior creates a window of opportunity for attackers to exploit the speculative execution capabilities of the processor, potentially gaining access to sensitive information that was previously protected by the TSX disable mechanism. The vulnerability affects both bare-metal systems and virtualized environments, making it particularly concerning for cloud computing and enterprise deployments where multiple tenants share hardware resources.
The operational impact of CVE-2021-28690 extends beyond simple security concerns to potentially compromise the integrity and confidentiality of data processing on affected systems. Systems that rely on TSX disable as their primary TAA mitigation strategy become vulnerable to attacks during the brief period between system resume and the restoration of proper security settings. This vulnerability is particularly dangerous in environments where sensitive data is processed, such as financial services, healthcare systems, or government networks, where the potential for data leakage through speculative execution attacks could result in significant financial and reputational damage. The vulnerability also impacts virtualized environments where hypervisors may not properly manage the TSX_CTRL register state across guest VM transitions, potentially affecting multiple virtual machines running on the same physical hardware.
Mitigation strategies for CVE-2021-28690 require immediate attention from system administrators and security teams to ensure proper restoration of TSX_CTRL register settings after system suspend operations. The most effective approach involves implementing firmware or kernel-level patches that automatically restore the proper TSX_CTRL register configuration during system resume from S3 states. System administrators should also consider implementing monitoring solutions to detect when TSX protections are not properly restored, allowing for immediate corrective action. Additionally, organizations should review their power management configurations to ensure that systems are not inadvertently triggering S3 suspend states without proper security state management. The mitigation efforts should align with industry best practices for speculative execution vulnerability management and should be coordinated with hardware vendors to ensure comprehensive protection across all system components. This vulnerability highlights the importance of proper state management during system transitions and underscores the need for robust security controls that persist across all system power states.