Date: Tue, 29 Oct 1996 05:05:44 -0600 (CST) From: Gary Clark II <gclarkii@main.gbdata.com> To: johnson@charming.nrtc.northrop.com Cc: questions@freebsd.org Subject: Re: Why is PSL_VM excluded from USERCHANGE macro? Message-ID: <199610291105.FAA13009@main.gbdata.com> In-Reply-To: <9610282237.AA07533@charming.nrtc.northrop.com> from "johnson@charming.nrtc.northrop.com" at "Oct 28, 96 02:37:49 pm"
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johnson@charming.nrtc.northrop.com wrote: > > > My question: Why is PSL_VM excluded from the set that the user can > modify? (If PSL_VM is set in EFLAG, the processor starts executing in > Virtual 8086 mode.) > > What would the dangers be to system integrity if a user process started > executing in Virtual 8086 mode? Because to run in VM86 mode you have to do a fair of amount of setup. If this is not done, nasty things can happen. > > While the processor is executing in Virtual 8086 mode, the paging hardware > still is enabled. It would appear that a user process operating in Virtual > 8086 mode could do no harm to the kernel data structures or otherwise > compromise the security of the machine. It might be useful to permit processes > to operate in Virtual 8086 mode, for purposes of creating an operating > environment to support execution of old 8086 code. It requires ALOT more than just running in VM86 mode. I wish it was that easy:) > > > Thanks, > > Greg Johnson > johnson@nrtc.northrop.com > Gary -- Gary Clark II (N5VMF) | I speak only for myself and "maybe" my company gclarkii@GBData.COM | Member of the FreeBSD Doc Team Providing Internet and ISP startups mail info@GBData.COM for information FreeBSD FAQ at ftp://ftp.FreeBSD.ORG/pub/FreeBSD/docs/freebsd-faq.ascii
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