Messages in this thread | | | Subject | Re: [PATCH v2 12/12] iommu: Do not allow IOMMU passthrough with Secure Launch | From | Ross Philipson <> | Date | Wed, 30 Jun 2021 05:50:20 -0400 |
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On 6/21/21 5:15 PM, Andy Lutomirski wrote: > On Mon, Jun 21, 2021 at 10:51 AM Ross Philipson > <ross.philipson@oracle.com> wrote: >> >> On 6/18/21 2:32 PM, Robin Murphy wrote: >>> On 2021-06-18 17:12, Ross Philipson wrote: >>>> The IOMMU should always be set to default translated type after >>>> the PMRs are disabled to protect the MLE from DMA. >>>> >>>> Signed-off-by: Ross Philipson <ross.philipson@oracle.com> >>>> --- >>>> drivers/iommu/intel/iommu.c | 5 +++++ >>>> drivers/iommu/iommu.c | 6 +++++- >>>> 2 files changed, 10 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c >>>> index be35284..4f0256d 100644 >>>> --- a/drivers/iommu/intel/iommu.c >>>> +++ b/drivers/iommu/intel/iommu.c >>>> @@ -41,6 +41,7 @@ >>>> #include <linux/dma-direct.h> >>>> #include <linux/crash_dump.h> >>>> #include <linux/numa.h> >>>> +#include <linux/slaunch.h> >>>> #include <asm/irq_remapping.h> >>>> #include <asm/cacheflush.h> >>>> #include <asm/iommu.h> >>>> @@ -2877,6 +2878,10 @@ static bool device_is_rmrr_locked(struct device >>>> *dev) >>>> */ >>>> static int device_def_domain_type(struct device *dev) >>>> { >>>> + /* Do not allow identity domain when Secure Launch is configured */ >>>> + if (slaunch_get_flags() & SL_FLAG_ACTIVE) >>>> + return IOMMU_DOMAIN_DMA; >>> >>> Is this specific to Intel? It seems like it could easily be done >>> commonly like the check for untrusted external devices. >> >> It is currently Intel only but that will change. I will look into what >> you suggest. >> >>> >>>> + >>>> if (dev_is_pci(dev)) { >>>> struct pci_dev *pdev = to_pci_dev(dev); >>>> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c >>>> index 808ab70d..d49b7dd 100644 >>>> --- a/drivers/iommu/iommu.c >>>> +++ b/drivers/iommu/iommu.c >>>> @@ -23,6 +23,7 @@ >>>> #include <linux/property.h> >>>> #include <linux/fsl/mc.h> >>>> #include <linux/module.h> >>>> +#include <linux/slaunch.h> >>>> #include <trace/events/iommu.h> >>>> static struct kset *iommu_group_kset; >>>> @@ -2761,7 +2762,10 @@ void iommu_set_default_passthrough(bool cmd_line) >>>> { >>>> if (cmd_line) >>>> iommu_cmd_line |= IOMMU_CMD_LINE_DMA_API; >>>> - iommu_def_domain_type = IOMMU_DOMAIN_IDENTITY; >>>> + >>>> + /* Do not allow identity domain when Secure Launch is configured */ >>>> + if (!(slaunch_get_flags() & SL_FLAG_ACTIVE)) >>>> + iommu_def_domain_type = IOMMU_DOMAIN_IDENTITY; >>> >>> Quietly ignoring the setting and possibly leaving iommu_def_domain_type >>> uninitialised (note that 0 is not actually a usable type) doesn't seem >>> great. AFAICS this probably warrants similar treatment to the >> >> Ok so I guess it would be better to set it to IOMMU_DOMAIN_DMA event >> though passthrough was requested. Or perhaps something more is needed here? >> >>> mem_encrypt_active() case - there doesn't seem a great deal of value in >>> trying to save users from themselves if they care about measured boot >>> yet explicitly pass options which may compromise measured boot. If you >>> really want to go down that route there's at least the sysfs interface >>> you'd need to nobble as well, not to mention the various ways of >>> completely disabling IOMMUs... >> >> Doing a secure launch with the kernel is not a general purpose user use >> case. A lot of work is done to secure the environment. Allowing >> passthrough mode would leave the secure launch kernel exposed to DMA. I >> think what we are trying to do here is what we intend though there may >> be a better way or perhaps it is incomplete as you suggest. >> > > I don't really like all these special cases. Generically, what you're > trying to do is (AFAICT) to get the kernel to run in a mode in which > it does its best not to trust attached devices. Nothing about this is > specific to Secure Launch. There are plenty of scenarios in which > this the case: > > - Virtual devices in a VM host outside the TCB, e.g. VDUSE, Xen > device domains (did I get the name right), whatever tricks QEMU has, > etc. > - SRTM / DRTM technologies (including but not limited to Secure > Launch -- plain old Secure Boot can work like this too). > - Secure guest technologies, including but not limited to TDX and SEV. > - Any computer with a USB-C port or other external DMA-capable port. > - Regular computers in which the admin wants to enable this mode for > whatever reason. > > Can you folks all please agree on a coordinated way for a Linux kernel > to configure itself appropriately? Or to be configured via initramfs, > boot option, or some other trusted source of configuration supplied at > boot time? We don't need a whole bunch of if (TDX), if (SEV), if > (secure launch), if (I have a USB-C port with PCIe exposed), if > (running on Xen), and similar checks all over the place. >
I replied to Robin Murphy in another thread. As far as the IOMMU is concerned, I think we need to rethink our approach. As to the other technologies you mention here, we have not considered special casing anything at this point.
Thanks Ross
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