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Kernel page-table isolation (KPTI or PTI, [1] previously called KAISER) [2] [3] is a Linux kernel feature that mitigates the Meltdown security vulnerability (affecting mainly Intel's x86 CPUs) [4] and improves kernel hardening against attempts to bypass kernel address space layout randomization (KASLR).
For example, before kernel page-table isolation was introduced, most versions of Linux mapped all physical memory into the address space of every user-space process; the mapped addresses are (mostly) protected, making them unreadable from user-space and accessible only when transitioned into the kernel. The existence of these mappings makes ...
The second "shadow" page table contains a copy of all of the user-space mappings, but leaves out the kernel side. Instead, there is a minimal set of kernel-space mappings that provides the information needed to handle system calls and interrupts, but no more."
The multilevel page table may keep a few of the smaller page tables to cover just the top and bottom parts of memory and create new ones only when strictly necessary. Now, each of these smaller page tables are linked together by a master page table, effectively creating a tree data structure. There need not be only two levels, but possibly ...
Load the required data into the available page frame. Update the page table to refer to the new page frame. Return control to the program, transparently retrying the instruction that caused the page fault. When all page frames are in use, the operating system must select a page frame to reuse for the page the program now needs.
Address space layout randomization (ASLR) is a computer security technique involved in preventing exploitation of memory corruption vulnerabilities. [1] In order to prevent an attacker from reliably redirecting code execution to, for example, a particular exploited function in memory, ASLR randomly arranges the address space positions of key data areas of a process, including the base of the ...
There may be a single page table, a page table for each process, a page table for each segment, or a hierarchy of page tables, depending on the architecture and the OS. The page tables are usually invisible to the process. Page tables make it easier to allocate additional memory, as each new page can be allocated from anywhere in physical memory.
cgroups (abbreviated from control groups) is a Linux kernel feature that limits, accounts for, and isolates the resource usage (CPU, memory, disk I/O, etc. [1]) of a collection of processes.