CVE-2025-38434: 
MinimOS vulnerability analysis and mitigation

CVE-2025-38434 is a vulnerability discovered in the Linux kernel related to the TASK_SIZE_MAX implementation for the __access_ok() function on RISC-V architecture. The vulnerability was disclosed on July 25, 2025, and affects the Linux kernel's memory access validation mechanism (NVD, RedHat).

The vulnerability stems from a change that set TASK_SIZE_MAX to LONG_MAX to optimize access_ok() function, instead of using the default TASK_SIZE value. While the optimization was intended to simplify kernel address filtering (as user addresses are less than LONG_MAX and kernel addresses are greater than LONG_MAX), it introduced a security flaw. The issue occurs because addresses between TASK_SIZE and LONG_MAX, while not valid user addresses, were being allowed to pass through access_ok(). The vulnerability becomes particularly problematic with get_user_pages_fast() function, which accepts addresses in this range, affecting services like futex() (RedHat).

The vulnerability has been assigned a moderate severity rating with a CVSS 3.1 base score indicating local access requirements (AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H). The primary impact is on system availability, as the flaw could potentially lead to system instability or crashes when exploited (RedHat).

The vulnerability has been resolved by reverting the commit that changed TASK_SIZE_MAX to LONG_MAX. The fix returns TASK_SIZE_MAX to its default value of TASK_SIZE. While this solution results in reduced performance due to more expensive computation requirements, it prioritizes security over optimization (RedHat).