From owner-freebsd-hackers@FreeBSD.ORG  Mon Apr 13 11:25:13 2015
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In-Reply-To: <alpine.BSF.2.20.1504130928460.921@laptop.wojtek.intra>
References: <alpine.BSF.2.20.1504130928460.921@laptop.wojtek.intra>
Date: Mon, 13 Apr 2015 13:25:05 +0200
Message-ID: <CAPQ4ffurO0yrmSUKH911sQQau57mi1SU2UfBUt_Pr7VmCqt7ww@mail.gmail.com>
Subject: Re: another question - VM mappings
From: Oliver Pinter <oliver.pinter@hardenedbsd.org>
To: Wojciech Puchar <wojtek@puchar.net>
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Cc: "freebsd-hackers@freebsd.org" <freebsd-hackers@freebsd.org>
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Under amd64 exists an so called shared-page - similar to linux's vdso
mechanism - https://github.com/freebsd/freebsd/blob/master/sys/kern/kern_exec.c#L1045
.

This page is double mapped with user-space and with kernel. From
security reason it's only RO, otherwise, when mapped with RW or RWX,
then you could write kernel memory from user-space.

On Mon, Apr 13, 2015 at 9:31 AM, Wojciech Puchar <wojtek@puchar.net> wrote:
> below is mapping for very simple process (no libc etc)
>
> [wojtek@laptop ~]$ procstat -v 917
>   PID              START                END PRT  RES PRES REF SHD   FL TP
> PATH
>   917           0x400000           0x401000 r-x    1    0   1   0 CN-- vn
> /home/wojtek/test/1
>   917           0x600000           0x601000 rw-    1    0   1   0 ---- df
>   917     0x7ffffffdf000     0x7ffffffff000 rw-    1    0   1   0 ---D df
>   917     0x7ffffffff000     0x800000000000 r-x    0    0  39   0 ---- ph
>
>
> what is "ph" mapping and why read&executable?