Date: Wed, 27 Aug 2008 16:00:24 -0400 (EDT)
From: Jan Engelhardt <jengelh@medozas.de>
To: Jeff Dike <jdike@addtoit.com>
cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: Is SKAS still required for UML
In-Reply-To: <20080827190655.GB12522@c2.user-mode-linux.org>
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References: <alpine.LNX.1.10.0808271251170.1378@fbirervta.pbzchgretzou.qr> <20080827190655.GB12522@c2.user-mode-linux.org>
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On Wednesday 2008-08-27 15:06, Jeff Dike wrote:
>On Wed, Aug 27, 2008 at 12:57:53PM -0400, Jan Engelhardt wrote:
>> 
>> I tried to put this to a test, and actually failed to modify the 
>> UML kernel/memory image from within it. I had a simple kernel module 
>> with 'int val = 2;' and upon loading this, done printk("Val is at %p\n", 
>> &val); to get to know the address. A userspace program inside the UML 
>> then tried to dereference that address and read the value, but that 
>> ended in a segfault. /proc/xxx/maps also does not show the UML kernel 
>> being mapped in any process inside the UML. Note that I was running in 
>> SKAS0 mode, both host and guest are all 64-bit. Is the NX bit of the 
>> 64-bit platform securing things off, or has SKAS3 become sort of 
>> obsolete?
>
>SKAS3 is still a significant performance boost.

In tests of mine, oggenc in SKAS0 mode ran at 95% of native speed, which 
is pretty good.
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