Pkru

If supported by hardware, pkru, each mapped user linear address has an associated 4-bit protection key, pkru. A new per-thread PKRU hardware register determines, for each protection key, whether user-mode addresses with that protection key may be read or written. Only one key may apply to a given range pkru a time.

Want to link to this manual page? Skip site navigation 1 Skip section navigation 2 Header And Logo. Peripheral Links. Donate to FreeBSD. The mechanism gives safety measures which can be used to avoid incidental read or modification of sensitive memory, or as a debugging feature. It cannot guard against conscious accesses since permissions are user-controllable.

Pkru

.

The protection prevents the system from accessing pkru addresses as well as the user applications. If access is not zero, read access is permitted. Existing mappings are changed to use key index zero in page table entries, pkru.

.

Memory protection consists in managing access rights of memory pages, either to avoid bugs or preventing malicious behavior. This is usually done through system calls, for instance with mprotect on Linux, because modification of the page table entries requires privileged access. MPK also referred as PKU for Protection Keys for Userspace is a userspace hardware mechanism to control page table permissions, it works by tagging memory pages with protection keys using 4 previously unused bits, in other words we can use up to 16 distinct keys to tag our pages. Once a page is tagged we can change its protection rights at will, from userspace. But, because updating page table entries PTE requires privileged access, a system call is still necessary to tag the pages with a given key in the first place.

Pkru

List Str Mega Menu. Hot Line. University Executive Board. University Council Board. University Academic Council Board. University Affairs Board. Faculty Senate Board. Tracing, Inspection and Evaluation Board.

Clip art swings

If the value pointed to by access is zero after the call, no read or write permissions is granted for map- pings which are assigned the key keyidx. Protection keys require that the system uses 4-level paging also called long mode , which means that it is only available on amd64 sys- tem. The key indexes written into the page table entries are managed by the sysarch syscall. Donate to FreeBSD. FreeBSD Only one key may apply to a given range at a time. It cannot guard against conscious accesses since permissions are user-controllable. FreeBSD The system provides convenient library helpers for both the syscall and the instructions, described below. Starting address is truncated to the page start, and the end is rounded up to the end of the page.

.

Both bit and bit applications can use protection keys. They are re-estab- lished when the current mapping is destroyed and a new mapping is created in any sub-range of the specified range. Only assign the key if the range does not have any other keys assigned including the zero key. The keys assigned to the range are persistent. If supported by hardware, each mapped user linear address has an asso- ciated 4-bit protection key. Please direct any comments about this manual page service to Ben Bullock. All rights reserved. The protection prevents the system from accessing user addresses as well as the user applications. Privacy policy. A new per-thread PKRU hardware register determines, for each protection key, whether user-mode addresses with that protection key may be read or written.