linux-kernel - Re: Big reserved mappings on x86

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20070425084931.GC355@devserv.devel.redhat.com>
Date:	Wed, 25 Apr 2007 04:49:31 -0400
From:	Jakub Jelinek <jakub@...hat.com>
To:	Jan Engelhardt <jengelh@...ux01.gwdg.de>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Big reserved mappings on x86_64

On Wed, Apr 25, 2007 at 10:42:20AM +0200, Jan Engelhardt wrote:
> I actually took a look at `pmap $$`, which reveals that a lot of shared 
> libraries map 2044K or 2048K unreadable-unwritable-private 
> mappings...for _what_ purpose?
> 
> 10:37 opteron:~ > pmap $$
> 4403: bash
> START       SIZE     RSS   DIRTY PERM MAPPING
> 2ae6cca70000    212K    172K      0K r-xp /lib64/libreadline.so.5.2
> 2ae6ccaa5000   2044K      0K      0K ---p /lib64/libreadline.so.5.2 <--
> 2ae6ccca4000      4K      4K      4K r--p /lib64/libreadline.so.5.2
> 2ae6ccca5000     28K     28K     28K rw-p /lib64/libreadline.so.5.2
> 2ae6cccac000      8K      8K      8K rw-p [anon]
> 2ae6cccae000     28K     16K      0K r-xp /lib64/libhistory.so.5.2
> 2ae6cccb5000   2048K      0K      0K ---p /lib64/libhistory.so.5.2 <--
> 2ae6cceb5000      8K      8K      8K rw-p /lib64/libhistory.so.5.2
> 2ae6cceb7000    320K    208K      0K r-xp /lib64/libncurses.so.5.5
> 2ae6ccf07000   2048K      0K      0K ---p /lib64/libncurses.so.5.5 <--
> 2ae6cd107000     48K     48K     48K r--p /lib64/libncurses.so.5.5
> 2ae6cd113000     28K     28K     28K rw-p /lib64/libncurses.so.5.5
> [...]
> 
> What could these ominous mappings be? Does anyone else see that - 
> perhaps someone with x86_64 && !(opensuse 10.2)?

While i386 only supports 4KB pages, x86_64 ELF objects ought to support
up to 2MB pages.  The gap between read-only/executable and writable segments
is intentionally mapped PROT_NONE, so that other things aren't mapped in
between the segments.

	Jakub
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/