97 lines
3.2 KiB
Groff
97 lines
3.2 KiB
Groff
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.\" $OpenBSD: mimmutable.2,v 1.3 2022/11/06 20:15:44 jmc Exp $
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.\"
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.\" Copyright (c) 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)mimmutable.2 8.1 (Berkeley) 6/9/93
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.\"
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.Dd $Mdocdate: November 6 2022 $
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.Dt MIMMUTABLE 2
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.Os
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.Sh NAME
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.Nm mimmutable
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.Nd control the immutability of pages
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.Sh SYNOPSIS
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.In sys/mman.h
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.Ft int
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.Fn mimmutable "void *addr" "size_t len"
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.Sh DESCRIPTION
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The
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.Fn mimmutable
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system call
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changes currently mapped pages in the region to be marked immutable,
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which means their protection or mapping may not be changed in the future.
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.Xr mmap 2 ,
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.Xr mprotect 2 ,
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and
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.Xr munmap 2
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to pages marked immutable will return with error
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.Er EPERM .
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.Pp
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Unmapped pages in the region do not retain immutability, but this
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behaviour should not be relied upon.
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.Pp
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Not all implementations will guarantee that the immutable characteristic
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can be set on a page basis;
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the granularity of changes may be as large as an entire region.
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.Sh RETURN VALUES
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.Rv -std
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.Sh ERRORS
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The
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.Fn mimmutable
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system call will fail if:
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.Bl -tag -width Er
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.It Bq Er EINVAL
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The virtual address range specified by the
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.Fa addr
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and
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.Fa len
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arguments is not valid.
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.El
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.Sh SEE ALSO
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.Xr mmap 2 ,
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.Xr mprotect 2 ,
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.Xr munmap 2
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.Sh HISTORY
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The
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.Fn mimmutable
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function first appeared in
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.Ox 7.3 .
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.Sh CAVEATS
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At present,
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.Xr mprotect 2
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may reduce permissions on immutable pages marked
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.Dv PROT_READ | PROT_WRITE
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to the less permissive
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.Dv PROT_READ .
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This one-way operation is permitted for an introductory period to observe how
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software uses this mechanism.
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It may change to require explicit mutable region annotation with
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.Va __attribute__((section(".openbsd.mutable")))
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and explicit calls to
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.Fn mimmutable .
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