|
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH] VT-d: improve RMRR validity checking
Hello Weidong, Is it possible to enable/disable DRHD's and RMRR's after boot ? For example if one would hotplug a pci device, that wasn't existent on boot .. What would happen considering security ? Is it possible to enable DRHD for that device although it was non existent at boot ? -- Sander Monday, January 25, 2010, 8:56:24 AM, you wrote: > Noboru Iwamatsu wrote: >> Weidong, >> >> I read the patch and the following thread. >> >> I understood what you mean, but I think it's better to >> limit the scope of "force_iommu". >> And I believe RMRR should be checked as same as DRHD. >> >> What I thought about DRHD is: >> If all devices under the scope of the DRHD are non-existent, >> this DRHD is invalid but safely ignorable, so ignore it. >> > No, we cannot ignore it if iommu=force. The invisible device may be > disabled, not really non-existent. it is possibly that it is re-enabled > by malfunctional s/w. So when iommu=force, we should not ignore any > DRHD. We ignores it just to workaround the BIOS issue you encountered. >> If some devices under the scope of the DRHD are non-existent, >> this DRHD is invalid, so disable VT-d unless "iommu=force" >> option is specified. >> When "iommu=force" option is specified, even the invalid DRHD >> will be registered, because DRHD that has some existent devices >> must not be ignored due to security reasons. >> >> About the RMRR: >> If all devices under the scope of the RMRR are non-existent, >> this RMMR is invalid but ignorable, so ignore it. >> If some devices under the scope of the RMRR are non-existent, >> this RMRR is invalid, so disable VT-d unless "iommu=force" >> > RMRR is much different from DRHD, it's just reversed memories for > specific devices (now only Intel IGD and USB contollers need RMRR), it's > no security issue like described above. > if "all" devices under the scope of the RMRR are non-existent, we > can ignore the RMRR because no devices will use it. > if some" devices under the scope of the RMRR are non-existent, we > cannot ignore the RMRR, because there are still some devices want to use > it. I think we needn't to disable VT-d because it won't cause any > issues. Of course, we also can disable VT-d for this case strictly. >> option is specified. When "iommu=force" option is specified, >> the invalid RMRR is ignored (it's safe). >> >> >> I attach the patch. >> >> What do you think? >> > Noboru, > I think it need not to change current code. BTW, your patch is not based > on latest Xen. > Regards, > Weidong >> Regards, >> Noboru. >> >> >>> I implemented a patch and attached. >>> >>> patch description: >>> In order to make Xen more defensive to VT-d related BIOS issue, this >>> patch ignores a DRHD if all devices under its scope are not pci >>> discoverable, and regards a DRHD as invalid and then disable whole VT-d >>> if some devices under its scope are not pci discoverable. But if >>> iommu=force is set, it will enable all DRHDs reported by BIOS, to avoid >>> any security vulnerability with malicious s/s re-enabling "supposed >>> disabled" devices. Pls note that we don't know the devices under the >>> "Include_all" DRHD are existent or not, because the scope of >>> "Include_all" DRHD won't enumerate common pci device, it only enumerates >>> I/OxAPIC and HPET devices. >>> >>> Signed-off-by: Noboru Iwamatsu <n_iwamatsu@xxxxxxxxxxxxxx> >>> Signed-off-by: Weidong Han <weidong.han@xxxxxxxxx> >>> >>> >>> Noboru, pls test the patch on your machine? >>> >>> Joe, could you review the patch? and pls ACK it if it's fine for you. >>> >>> Regards, >>> Weidong >>> >>> Noboru Iwamatsu wrote: >>> >>>> Thanks, >>>> >>>> I understood. >>>> >>>> >>>>> Noboru Iwamatsu wrote: >>>>> >>>>>> Hi Weidong, >>>>>> >>>>>> I'm not sure why the security problem is caused by ignoring >>>>>> the DRHD that has only non-existent devices. >>>>>> >>>>>> Could you explain details or where to read the spec? >>>>>> >>>>> It's requested from security experts. The device that is not pci >>>>> discoverable may be re-enabled by malicious software. If its DRHD is not >>>>> enabled, the re-enabled device is not protected by VT-d. It will cause >>>>> security issue. >>>>> >>>>> >>>>>> As you saying, security is the top-priority. >>>>>> However, when iommu=force is specified, we should enable vt-d >>>>>> if there are some potential issues. >>>>>> Because users want to "force" anyway. >>>>>> >>>>> iommu=force was introduced to enable VT-d anyway for security purpose. I >>>>> plan to still enable those DRHDs that includes non-existed device when >>>>> iommu=force, otherwise ignore them. >>>>> >>>>> Regards, >>>>> Weidong >>>>> >>>>>> Regards, >>>>>> Noboru. >>>>>> >>>>>> >>>>>>> Keir Fraser wrote: >>>>>>> >>>>>>>> If we want to keep iommu=1 as default, then it is unacceptable to >>>>>>>> fail to >>>>>>>> boot on a fairly wide range of modern systems. We have to >>>>>>>> warn-and-disable, >>>>>>>> partially or completely, unless iommu=force is specified. Or we >>>>>>>> need to >>>>>>>> revert to iommu=0 as the default. >>>>>>>> >>>>>>>> What do you think, Weidong? >>>>>>>> >>>>>>> Yes. I agree to warn-and-disable for these BIOS issues, and consider >>>>>>> security more when iommu=force. Therefore I will implement a patch >>>>>>> based >>>>>>> on Nororu's patch. >>>>>>> >>>>>>> Regards, >>>>>>> Weidong >>>>>>> >>>>>>> >>>>>>>> -- Keir >>>>>>>> >>>>>>>> On 21/01/2010 14:17, "Sander Eikelenboom" <linux@xxxxxxxxxxxxxx> >>>>>>>> wrote: >>>>>>>> >>>>>>>> >>>>>>>>> Hello Weidong, >>>>>>>>> >>>>>>>>> The problem is most vendor's just don't fix it and ignore the >>>>>>>>> problem >>>>>>>>> completely. >>>>>>>>> Most often hiding them selves behind: come back when it's a problem >>>>>>>>> with >>>>>>>>> Microsoft Windows, that the only single thing we support (and no >>>>>>>>> other >>>>>>>>> software, so no vmware, no xen, no linux, perhaps even no >>>>>>>>> hypervisor) >>>>>>>>> Well I don't know if the virtual pc in windows 7 supports an iommu >>>>>>>>> now, but it >>>>>>>>> didn't in the past as far as i know, so any complain bounces off, >>>>>>>>> and >>>>>>>>> there it >>>>>>>>> all seems to end for them. >>>>>>>>> >>>>>>>>> Besides that i don't know if they do know what the problems with >>>>>>>>> there >>>>>>>>> implementation in BIOS is when someone reports it. >>>>>>>>> I think some behind the scenes pressure from Intel to vendors might >>>>>>>>> help to >>>>>>>>> solve some of them. >>>>>>>>> (my Q35 chipset, "Intel V-PRO" marketed motherboard (so much for >>>>>>>>> that) also >>>>>>>>> suffers RMRR problem when another graphics card is inserted which >>>>>>>>> switches off >>>>>>>>> the IGD). >>>>>>>>> >>>>>>>>> Although i think in my case your patch will work around that for me. >>>>>>>>> Perhaps a >>>>>>>>> third option is needed, which does all the workarounds possible and >>>>>>>>> warns >>>>>>>>> about potential security problem when requested ? >>>>>>>>> >>>>>>>>> -- >>>>>>>>> Sander >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>> Thursday, January 21, 2010, 1:46:39 PM, you wrote: >>>>>>>>> >>>>>>>>> >>>>>>>>>> Noboru Iwamatsu wrote: >>>>>>>>>> >>>>>>>>>>> Hi Weidong, >>>>>>>>>>> >>>>>>>>>>> I re-send the DRHD-fix patch. >>>>>>>>>>> >>>>>>>>>>> If DRHD does not have existent devices, ignore it. >>>>>>>>>>> If DRHD has both existent and non-existent devices, consider it >>>>>>>>>>> invalid >>>>>>>>>>> and not register. >>>>>>>>>>> >>>>>>>>>> Although you patch workarounds your buggy BIOS, but we still >>>>>>>>>> need to >>>>>>>>>> enable it for security purpose as I mentioned in previous mail. We >>>>>>>>>> needn't workaround / fix all BIOS issues in software. I think >>>>>>>>>> security >>>>>>>>>> is more important for this specific BIOS issue. Did you report the >>>>>>>>>> BIOS >>>>>>>>>> issue to your OEM vendor? maybe it's better to get it fixed in >>>>>>>>>> BIOS. >>>>>>>>>> Regards, >>>>>>>>>> Weidong >>>>>>>>>> >>>>>>>>>>> According to this patch and yours, my machine successfully booted >>>>>>>>>>> with vt-d enabled. >>>>>>>>>>> >>>>>>>>>>> Signed-off-by: Noboru Iwamatsu <n_iwamatsu@xxxxxxxxxxxxxx> >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>>> Keir Fraser wrote: >>>>>>>>>>>> >>>>>>>>>>>>> On 21/01/2010 10:19, "Weidong Han" <weidong.han@xxxxxxxxx> >>>>>>>>>>>>> wrote: >>>>>>>>>>>>> >>>>>>>>>>>>> >>>>>>>>>>>>>>> Sorry this is typo. >>>>>>>>>>>>>>> I mean: >>>>>>>>>>>>>>> So, I think RMRR that has no-existent device is "invalid" >>>>>>>>>>>>>>> and whole RMRR should be ignored. >>>>>>>>>>>>>>> >>>>>>>>>>>>>> looks reasonable. >>>>>>>>>>>>>> >>>>>>>>>>>>>> Keir, I Acks Noboru's rmrr patch. Or do you want us to merge >>>>>>>>>>>>>> them to one >>>>>>>>>>>>>> patch? >>>>>>>>>>>>>> >>>>>>>>>>>>> Merge them up, re-send with both sign-off and acked-by all in >>>>>>>>>>>>> one >>>>>>>>>>>>> email. >>>>>>>>>>>>> >>>>>>>>>>>>> Thanks, >>>>>>>>>>>>> Keir >>>>>>>>>>>>> >>>>>>>>>>>>> >>>>>>>>>>>> Sorry, I disagree with Noboru after thinking it again. If the >>>>>>>>>>>> RMRR >>>>>>>>>>>> has >>>>>>>>>>>> both no-existent device and also has existent devices in its >>>>>>>>>>>> scope, we >>>>>>>>>>>> should not ignore it because the existent devices under its scope >>>>>>>>>>>> will >>>>>>>>>>>> be impacted without the RMRR. so I suggest to print a warning >>>>>>>>>>>> instead of >>>>>>>>>>>> ignore it. Attached a patch for it. >>>>>>>>>>>> >>>>>>>>>>>> Signed-off-by: Weidong Han <weidong.han@xxxxxxxxx> >>>>>>>>>>>> >>>> >> >> -- Best regards, Sander mailto:linux@xxxxxxxxxxxxxx _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
|
 |
Lists.xenproject.org is hosted with RackSpace, monitoring our |