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 Signed-off-by: Weidong Han 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" 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 >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>>> Keir Fraser wrote: >>>>>>>>> >>>>>>>>>> On 21/01/2010 10:19, "Weidong Han" 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 >>>>>>>>> >>> > > >