CVE-2024-50182: In the Linux kernel, the following vulnerability has been resolved: secretmem: disable memfd_secret() if arch cannot se

A Linux kernel vulnerability (CVE-2024-50182) affected memfd_secret(), a system call that creates secret memory regions hidden from the kernel's direct map (a lookup table for physical memory). On some ARM64 systems, the function appeared to work but silently failed to actually hide the memory, defeating its security purpose. The fix makes memfd_secret() return an error code (-ENOSYS) on systems that cannot properly remove memory from the direct map, rather than silently failing.