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Makefile.inc
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__vdso_gettc.c
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pkru.3
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pkru.c
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Editing: pkru.3
.\" Copyright (c) 2019 The FreeBSD Foundation, Inc. .\" All rights reserved. .\" .\" This documentation was written by .\" Konstantin Belousov <kib@FreeBSD.org> under sponsorship .\" from the FreeBSD Foundation. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" .\" THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" $FreeBSD$ .\" .Dd February 16, 2019 .Dt PKRU 3 .Os .Sh NAME .Nm Protection Key Rights for User pages .Nd provide fast user-managed key-based access control for pages .Sh LIBRARY .Lb libc .Sh SYNOPSIS .In machine/sysarch.h .Ft int .Fn x86_pkru_get_perm "unsigned int keyidx" "int *access" "int *modify" .Ft int .Fn x86_pkru_set_perm "unsigned int keyidx" "int access" "int modify" .Ft int .Fo x86_pkru_protect_range .Fa "void *addr" .Fa "unsigned long len" .Fa "unsigned int keyidx" .Fa "int flag" .Fc .Ft int .Fn x86_pkru_unprotect_range "void *addr" "unsigned long len" .Sh DESCRIPTION The protection keys feature provides an additional mechanism, besides the normal page permissions as established by .Xr mmap 2 and .Xr mprotect 2 , to control access to user-mode addresses. 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. .Pp If supported by hardware, each mapped user linear address has an associated 4-bit protection key. 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. .Pp Only one key may apply to a given range at a time. The default protection key index is zero, it is used even if no key was explicitly assigned to the address, or if the key was removed. .Pp The protection prevents the system from accessing user addresses as well as the user applications. When a system call was unable to read or write user memory due to key protection, it returns the .Er EFAULT error code. Note that some side effects may have occurred if this error is reported. .Pp Protection keys require that the system uses 4-level paging (also called long mode), which means that it is only available on amd64 system. Both 64-bit and 32-bit applications can use protection keys. More information about the hardware feature is provided in the IA32 Software Developer's Manual published by Intel Corp. .Pp The key indexes written into the page table entries are managed by the .Fn sysarch syscall. Per-key permissions are managed using the user-mode instructions .Em RDPKRU and .Em WRPKRU . The system provides convenient library helpers for both the syscall and the instructions, described below. .Pp The .Fn x86_pkru_protect_range function assigns key .Fa keyidx to the range starting at .Fa addr and having length .Fa len . Starting address is truncated to the page start, and the end is rounded up to the end of the page. 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. .Pp The .Fa flags argument takes the logical OR of the following values: .Bl -tag -width .It Bq Va AMD64_PKRU_EXCL Only assign the key if the range does not have any other keys assigned (including the zero key). You must first remove any existing key with .Fn x86_pkru_unprotect_range in order for this request to succeed. If the .Va AMD64_PKRU_EXCL flag is not specified, .Fn x86_pkru_protect_range replaces any existing key. .It Bq Va AMD64_PKRU_PERSIST The keys assigned to the range are persistent. They are re-established when the current mapping is destroyed and a new mapping is created in any sub-range of the specified range. You must use a .Fn x86_pkru_unprotect_range call to forget the key. .El .Pp The .Fn x86_pkru_unprotect_range function removes any keys assigned to the specified range. Existing mappings are changed to use key index zero in page table entries. Keys are no longer considered installed for all mappings in the range, for the purposes of .Fn x86_pkru_protect_range with the .Va AMD64_PKRU_EXCL flag. .Pp The .Fn x86_pkru_get_perm function returns access rights for the key specified by the .Fn keyidx argument. If the value pointed to by .Fa access is zero after the call, no read or write permissions is granted for mappings which are assigned the key .Fn keyidx . If .Fa access is not zero, read access is permitted. The non-zero value of the variable pointed to by the .Fa modify argument indicates that write access is permitted. .Pp Conversely, the .Fn x86_pkru_set_perm establishes the access and modify permissions for the given key index as specified by its arguments. .Sh RETURN VALUES .Rv -std .Sh ERRORS .Bl -tag -width Er .It Bq Er EOPNOTSUPP The hardware does not support protection keys. .It Bq Er EINVAL The supplied key index is invalid (greater than 15). .It Bq Er EINVAL The supplied .Fa flags argument for .Fn x86_pkru_protect_range has reserved bits set. .It Bq Er EFAULT The supplied address range does not completely fit into the user-managed address range. .It Bq Er ENOMEM The memory shortage prevents the completion of the operation. .It Bq Er EBUSY The .Va AMD64_PKRU_EXCL flag was specified for .Fn x86_pkru_protect_range and the range already has defined protection keys. .El .Sh SEE ALSO .Xr mmap 2 , .Xr mprotect 2 , .Xr munmap 2 , .Xr sysarch 2 . .Sh STANDARDS The .Nm functions are non-standard and first appeared in .Fx 13.0 .
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