sys_mlock [mm/mlock.c]
Locks part of the calling process's virtual address space into RAM, preventing that memory from being paged to the swap area. All pages that contain a part of the specified address range are guaranteed to be resident in RAM when the call returns successfully; the pages are guaranteed to stay in RAM until later unlocked. Memory locking has two main applications: real-time algorithms and high-security data processing. Real-time applications require deterministic timing, and, like scheduling, paging is one major cause of unexpected program execution delays. Real-time applications will usually also switch to a real-time scheduler with sys_sched_setscheduler. Cryptographic security software often handles critical bytes like passwords or secret keys as data structures. As a result of paging, these secrets could be transferred onto a persistent swap store medium, where they might be accessible to the enemy long after the security software has erased the secrets in RAM and terminated. (But be aware that the suspend mode on laptops and some desktop computers will save a copy of the system's RAM to disk, regardless of memory locks.) Memory locks are not inherited by a child created via sys_fork and are automatically removed (unlocked) during an sys_execve or when the process terminates. The memory lock on an address range is automatically removed if the address range is unmapped via sys_munmap. Memory locks do not stack, i.e., pages which have been locked several times will be unlocked by a single call to sys_munlock for the corresponding range. Pages which are mapped to several locations or by several processes stay locked into RAM as long as they are locked at least at one location or by at least one process. Arguments
eax | 150
ebx | Starting address of a memory range to lock. sys_mlock automatically rounds the address down to the nearest page boundary.
ecx | Length of the memory range specified by ebx.
Return values If the system call succeeds the return value is 0. If the system call fails the return value is one of the following errno values:
`-ENOMEM` | `(Linux 2.6.9 and later) the caller had a non-zero RLIMIT_MEMLOCK soft resource limit, but tried to lock more memory than the limit permitted. This limit is not enforced if the process is privileged (CAP_IPC_LOCK). -or- Some of the specified address range does not correspond to mapped pages in the address space of the process.`
`-EPERM` | `(Linux 2.6.9 and later) the caller was not privileged (CAP_IPC_LOCK) and its RLIMIT_MEMLOCK soft resource limit was 0.`
`-EINVAL` | `ecx was negative.`
Remarks In Linux 2.6.8 and earlier, a process must be privileged (CAP_IPC_LOCK) in order to lock memory and the RLIMIT_MEMLOCK soft resource limit defines a limit on how much memory the process may lock. Since Linux 2.6.9, no limits are placed on the amount of memory that a privileged process can lock and the RLIMIT_MEMLOCK soft resource limit instead defines a limit on how much memory an unprivileged process may lock. Compatibility n/a