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

[Jan Kiszka <jan.kiszka@siemens.com>]

Daniel P. Berrange wrote:
> 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.

Ah, good to be reminded that we are not alone with our segmented OS here. ;)

That makes me realize that my patch lacks range checks for code
segments. I think I left it out as it is not that trivial...

Jan

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