Date: Fri, 8 Dec 2000 23:41:14 +0100 From: Stefan Esser <se@freebsd.org> To: Mike Silbersack <silby@silby.com> Cc: "Chad R. Larson" <chad@DCFinc.com>, mjacob@feral.com, gallatin@cs.duke.edu, ken@kdm.org, hackers@FreeBSD.ORG, stable@FreeBSD.ORG, Stefan Esser <se@freebsd.org> Subject: Re: Re: PCIOCGETCONF/PCIOCREAD requires write permission? Message-ID: <20001208234114.A1638@StefanEsser.FreeBSD.org> In-Reply-To: <Pine.BSF.4.21.0012081000010.24059-100000@achilles.silby.com>; from silby@silby.com on Fri, Dec 08, 2000 at 10:02:44AM -0600 References: <200012080707.AAA12102@freeway.dcfinc.com> <Pine.BSF.4.21.0012081000010.24059-100000@achilles.silby.com>
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On 2000-12-08 10:02 -0600, Mike Silbersack <silby@silby.com> wrote: > Seriously, though. There must be some way to abuse such direct access to > the pci configuration registers. Just because nobody has figured it out > how yet doesn't mean that enabling the feature is a good idea. Well, what makes you think, that nobody has figured out why read access to the pci config space registers might not be a good idea ? ;-) The reason is simple: There are a number of PCI devices that fail in a number of ways, if certain config space registers are accessed while the device is active. This is counterintuitive at first, but just try to read a config register beyond 0x80 from an NCR SCSI chip while it is executing SCRIPTS code ... The PCI spec made higher numbered config space registers implementation dependent. Some vendors mapped their devices' operational registers into config space, even though the spec never encouraged that (though I'm not sure that such an (ab)use of config registers was declared forbidden in later revisions of the spec.). Since there are a number of devices that could be severely impacted by read accesses to configuration space registers, we can't safely permit any user such read access. Root hopefully knows what he is doing and only accesses such registers that are meant to be accessed while the device is operating ... Regards, STefan To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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