Linux Kernel RISC-V Access Validation Vulnerability Reversion

A vulnerability in the Linux kernel's RISC-V architecture handling has been addressed by reverting a previous change that optimized user address validation. The original modification set the maximum user address to LONG_MAX, under the assumption that all user addresses are below this value. However, this oversight allowed certain invalid addresses to pass through the validation, as they were accepted by the 'get_user_pages_fast()' function, used by components like 'futex()'. The reversion restores the previous TASK_SIZE_MAX value, prioritizing correctness over performance.

Impact

The reversion of the optimization may lead to decreased performance in address validation, as the TASK_SIZE requires more computational resources compared to LONG_MAX.