Pkru

If supported by hardware, each pkru user linear address has an associated 4-bit protection key.

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. If supported by hardware, each mapped user linear address has an asso- ciated 4-bit protection key.

Pkru

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Go to:. Only pkru key may apply to a given range at a time. Both bit and bit applications can use protection keys, pkru.

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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. To allocate and free a key we also need to go through the kernel, on Linux the API is the following:.

Pkru

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The system provides convenient library helpers for both the syscall and the instructions, described below. Both bit and bit applications can use protection keys. Both bit and bit applications can use protection keys. Only one key may apply to a given range at a time. All rights reserved. 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 non-zero value of the variable pointed to by the modify argument indicates that write access is permitted. If access is not zero, read access is permitted. Starting address is truncated to the page start, and the end is rounded up to the end of the page. Existing mappings are changed to use key index zero in page table entries. It cannot guard against conscious accesses since permissions are user-controllable. Note that some side effects may have occurred if this error is reported. After a successfull call, the range has the specified key assigned, even if the key is zero and it did not change the page table entries. If the value pointed to by access is zero after the call, no read or write permissions is granted for mappings which are assigned the key keyidx. Copyright: The copyright notice of this manual page is here plain text.

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Peripheral Links. The protection keys feature provides an additional mechanism, besides the normal page permissions as established by mmap 2 and mprotect 2 , to control access to user-mode addresses. Skip site navigation 1 Skip section navigation 2 Header And Logo. FreeBSD The non-zero value of the variable pointed to by the modify argument indicates that write access is permitted. The key indexes written into the page table entries are managed by the sysarch syscall. 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. After a successfull call, the range has the specified key assigned, even if the key is zero and it did not change the page table entries. 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. 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. 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. If access is not zero, read access is permitted.