CVE-2015-2672 in Linux
Summary
by MITRE
The xsave/xrstor implementation in arch/x86/include/asm/xsave.h in the Linux kernel before 3.19.2 creates certain .altinstr_replacement pointers and consequently does not provide any protection against instruction faulting, which allows local users to cause a denial of service (panic) by triggering a fault, as demonstrated by an unaligned memory operand or a non-canonical address memory operand.
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Analysis
by VulDB Data Team • 07/27/2022
The vulnerability described in CVE-2015-2672 resides within the Linux kernel's implementation of xsave and xrstor instructions, which are part of the Intel extended processor state management framework. This flaw specifically affects systems running Linux kernel versions prior to 3.19.2 and represents a critical issue in the kernel's handling of processor state management during context switching operations. The vulnerability stems from improper pointer management within the .altinstr_replacement mechanism, which is designed to handle alternative instruction sequences for different processor capabilities.
The technical implementation flaw occurs in the arch/x86/include/asm/xsave.h header file where the xsave/xrstor functionality creates certain .altinstr_replacement pointers without adequate protection against instruction faulting conditions. These pointers are used to manage alternative instruction sequences that may be executed depending on processor capabilities and system configuration. When the kernel encounters unaligned memory operands or non-canonical address memory operands during xsave/xrstor operations, the faulty pointer management causes the system to fail to properly handle the instruction fault, leading to a kernel panic and complete system crash.
This vulnerability operates as a local privilege escalation vector that allows attackers with user-level access to trigger a denial of service condition that results in system-wide panic. The attack requires no special privileges beyond standard user access, making it particularly dangerous in multi-user environments where malicious users could exploit this weakness to disrupt system operations. The flaw specifically manifests when the system attempts to execute xsave/xrstor instructions with problematic memory operands, causing the kernel's fault handling mechanism to fail catastrophically.
The operational impact of this vulnerability extends beyond simple denial of service, as it represents a fundamental breakdown in the kernel's ability to manage processor state correctly. System administrators face the risk of unexpected system crashes and potential data loss when this vulnerability is exploited, particularly in mission-critical environments where system uptime is essential. The vulnerability also highlights the complexity of modern processor state management and the challenges of maintaining robust error handling in low-level kernel code that interfaces directly with hardware features.
The flaw aligns with CWE-129, which describes improper validation of array indices, and demonstrates how pointer management issues can lead to system instability. From an ATT&CK perspective, this vulnerability maps to T1068, which covers exploitation of remote services, and T1499, which covers network denial of service, though it operates locally. The vulnerability's impact is mitigated through kernel version updates that properly implement the .altinstr_replacement pointer management and ensure adequate protection against instruction faulting conditions. System administrators should prioritize upgrading to kernel versions 3.19.2 or later, which contain the necessary patches to address this issue. The fix involves proper initialization and validation of replacement pointers within the xsave/xrstor implementation, ensuring that instruction fault conditions are properly handled without causing system-wide panic.