CVE-2025-38434 is a vulnerability in the Linux kernel related to the incorrect definition of TASK_SIZE_MAX in the riscv architecture. A previous commit changed TASK_SIZE_MAX to LONG_MAX to optimize the access_ok() function, but this allowed addresses between TASK_SIZE and LONG_MAX, which are invalid user addresses, to pass unchecked. This caused issues with functions like get_user_pages_fast() used by futex(), potentially leading to denial of service. The fix reverts the commit, restoring TASK_SIZE_MAX to TASK_SIZE to ensure correctness at the cost of some performance.