Re: [Qemu-devel] [RFC][PATCH] x86: Optional segment type and limit checks - v2

[Daniel P. Berrange]

On Mon, Jul 14, 2008 at 12:34:48PM +0200, Jan Kiszka wrote:
> This is the second version of my segment type and register check. It
> reduces the impact on the translator code significantly, and it also
> fixes a bug of the "size" helper variant in the previous version.
> 
> The idea of this patch is to generate calls to a check helper only in
> case the user requested this support via "-seg-checks". This feature
> remains off by default as most x86 OSes do not care about protection via
> segmentation anymore (and it was even removed from 64-bit modes by the
> CPU vendors). 

Two current users of protection via segmentation I know of

 - 32-bit linux with the ExecShield capability will still use segmentation 
   to split the address space into executable vs non-executable regions, if
   the CPU doesn't have NX bit support.
 - 32-bit Xen uses segmentation for protecting the hypervisor.

Regards,
Daniel
-- 
|: Red Hat, Engineering, London   -o-   http://people.redhat.com/berrange/ :|
|: http://libvirt.org  -o-  http://virt-manager.org  -o-  http://ovirt.org :|
|: http://autobuild.org       -o-         http://search.cpan.org/~danberr/ :|
|: GnuPG: 7D3B9505  -o-  F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 :|