CVE-2024-26902: 
Linux Kernel vulnerability analysis and mitigation

A vulnerability in the Linux kernel's RISC-V Performance Monitoring Unit (PMU) overflow handler has been identified and tracked as CVE-2024-26902. The issue was discovered when using 'perf record -e branches' on the Sophgo SG2042 platform, where incorrect bit manipulation in the unsigned long overflowed_ctrs variable caused a kernel NULL pointer dereference (Kernel Git).

The vulnerability stems from improper bit manipulation when setting bits in the unsigned long overflowed_ctrs variable. The code incorrectly used (1 << idx) operation with integer type instead of the proper BIT() macro for unsigned long values. This resulted in a NULL pointer dereference at virtual address 0x98, triggering a kernel panic. The issue affects Linux kernel versions up to 6.6.23 and versions from 6.7 up to 6.7.11. The vulnerability has been assigned a CVSS v3.1 base score of 5.5 (MEDIUM) with vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H (NVD).

When triggered, the vulnerability causes a kernel panic due to a NULL pointer dereference in the interrupt handler, leading to system availability issues. This primarily affects systems using RISC-V architecture when utilizing the performance monitoring features (Kernel Git).

The vulnerability can be triggered by running 'perf record -e branches' on affected RISC-V systems, specifically demonstrated on the Sophgo SG2042 platform. The local nature of the exploit and the requirement for valid user privileges to access performance monitoring features limit the potential attack surface (NVD).

The vulnerability has been patched by replacing the (1 << idx) operations with the proper BIT() macro in the RISC-V PMU overflow handler code. The fix has been implemented in the Linux kernel through multiple commits, including 34b567868777e9fd39ec5333969728a7f0cf179c. Users should upgrade to Linux kernel version 6.6.23 or later, or 6.7.11 or later to address this vulnerability (Kernel Git).