Messages in this thread |  | | Date | Thu, 7 Feb 2013 18:27:01 +0100 | From | Joerg Roedel <> | Subject | Re: [PATCH] intel_iommu: Disable vfio and kvm interrupt assignment when unsafe |
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On Thu, Feb 07, 2013 at 08:29:42AM -0800, Andy Lutomirski wrote: > On Thu, Feb 7, 2013 at 3:33 AM, Joerg Roedel <joro@8bytes.org> wrote: > > On Wed, Feb 06, 2013 at 07:08:24PM -0800, Andy Lutomirski wrote: > >> - if (x2apic_present) > >> - WARN(1, KERN_WARNING > >> - "Failed to enable irq remapping. You are vulnerable to irq-injection attacks.\n"); > >> - > >> + irq_remapping_is_secure = 0; > >> return -1; > >> } > > > > Why do you remove this warning? It seems unrelated to the rest of the > > patch. > > The idea is that setting irq_remapping_is_secure = 0 makes you (much > less) vulnerable to irq-injection attacks: you're vulnerable to > malicious hardware but not to attack via vfio or kvm, because those > paths are disabled. > > I'd have no problem leaving the warning in and letting whoever manages > to trigger it and get annoyed fix it. FWIW, it's actually likely to > be interesting if the warning hits.
Hmm, looking into the intel_irq_remapping.c version in the tip tree makes me wonder even more.
First, I wonder why the warning only hits when an x2apic is present. The function is not x2apic-specific and the vulnerability also exists in xapic mode. So that dependency can be removed.
Second, I think that it should be a pr_warn instead of a full WARN. When IRQ remapping could not be enabled it's most likely because of the BIOS or the hardware. So a message in the kernel log will do and the backtrace provides no additional value.
Same is true for the warning in the function iommu_set_irq_remapping():
if (sts & DMA_GSTS_CFIS) WARN(1, KERN_WARNING "Compatibility-format IRQs enabled despite intr remapping;\n" "you are vulnerable to IRQ injection.\n");
From what I can see this condition depends only on the hardware too. So a simple pr_warn() provides the same amount of information.
Regards,
Joerg
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