On Thu, Mar 21, 2019 at 05:51:11PM +0200, Jarkko Sakkinen wrote:
> On Tue, Mar 19, 2019 at 02:19:51PM -0700, Sean Christopherson wrote:
> > IMO we should get rid of SGX_POWER_LOST_ENCLAVE and the SUSPEND flag.
> >
> > - Userspace needs to handle -EFAULT cleanly even if we hook into
> > suspend/hibernate via sgx_encl_pm_notifier(), e.g. to handle virtual
> > machine migration.
> > - In the event that suspend is canceled after sgx_encl_pm_notifier()
> > runs, we'll have prematurely invalidated the enclave.
> > - Invalidating all enclaves could be slow on a system with GBs of EPC,
> > i.e. probably not the best thing to do in the suspend path.
> >
> > Removing SGX_POWER_LOST_ENCLAVE means we can drop all of the pm_notifier()
> > code, which will likely save us a bit of maintenance down the line.
>
> I don't disgree. Isn't it a racy flag in the VM context i.e. because
> suspend can happen without SGX core noticing it (running inside a VM)?
> That would a bug.
...
> > > +#ifdef CONFIG_ACPI
> > > +static struct acpi_device_id sgx_device_ids[] = {
> > > + {"INT0E0C", 0},
> > > + {"", 0},
> > > +};
> > > +MODULE_DEVICE_TABLE(acpi, sgx_device_ids);
> > > +#endif
> > > +
> > > +static struct platform_driver sgx_drv = {
> > > + .probe = sgx_drv_probe,
> > > + .remove = sgx_drv_remove,
> > > + .driver = {
> > > + .name = "sgx",
> > > + .acpi_match_table = ACPI_PTR(sgx_device_ids),
> > > + },
> > > +};
> >
> > Utilizing the platform driver is unnecessary, adds complexity and IMO is
> > flat out wrong given the current direction of implementing SGX as a
> > full-blooded architectural feature.
> >
> > - All hardware information is readily available via CPUID
> > - arch_initcall hooks obviates the need for ACPI autoprobe
> > - EPC manager assumes it has full control over all EPC, i.e. EPC
> > sections are not managed as independent "devices"
> > - BIOS will enumerate a single ACPI entry regardless of the number
> > of EPC sections, i.e. the ACPI entry is *only* useful for probing
> > - Userspace driver matches the EPC device, but doesn't actually
> > "own" the EPC
>
> It is for hotplugging. I don't really have strong opinions of this but
> having a driver for uapi allows things like blacklisting sgx.
Hotplugging what? EPC can't be hotplugged, EPC enumeration through CPUID
won't change post-boot and the ACPI entry can't be relied upon for EPC
base/size information when there are multiple EPC sections.
> > > +
> > > +static int __init sgx_drv_subsys_init(void)
> > > +{
> > > + int ret;
> > > +
> > > + ret = bus_register(&sgx_bus_type);
> >
> > Do we really need a bus/class? Allocating a chrdev region also seems like
> > overkill. At this point there is exactly one SGX device, and while there
> > is a pretty good chance we'll end up with a virtualization specific device
> > for exposing EPC to guest, there's no guarantee said device will be SGX
> > specific. Using a dynamic miscdevice would eliminate a big chunk of code.
>
> AFAIK misc is not recommended for any new drivers as it has suvere
> limitations like not allowing to add non-racy sysfs attributes. Whatever
> the solution is, lets not use misc.
Ah right, forgot about that.
> > > + if (ret)
> > > + return ret;
> > > +
> > > + ret = alloc_chrdev_region(&sgx_devt, 0, SGX_DRV_NR_DEVICES, "sgx");
> > > + if (ret < 0) {
> > > + bus_unregister(&sgx_bus_type);
> > > + return ret;
> > > + }
> > > +
> > > + return 0;
> > > +}
...
> > > +static void sgx_vma_open(struct vm_area_struct *vma)
> > > +{
> > > + struct sgx_encl *encl = vma->vm_private_data;
> > > + struct sgx_encl_mm *mm;
> > > +
> > > + if (!encl)
> > > + return;
> > > +
> > > + if (encl->flags & SGX_ENCL_DEAD)
> > > + goto out;
> > > +
> > > + mm = sgx_encl_get_mm(encl, vma->vm_mm);
> > > + if (!mm) {
> > > + mm = kzalloc(sizeof(*mm), GFP_KERNEL);
> > > + if (!mm) {
> > > + encl->flags |= SGX_ENCL_DEAD;
> >
> > Failure to allocate memory for one user of the enclave shouldn't kill
> > the enclave, e.g. failing during fork() shouldn't kill the enclave in
> > the the parent. And marking an enclave dead without holding its lock
> > is all kinds of bad.
>
> This is almost non-existent occasion. Agree with the locking though..
> And I'm open for other fallbacks but given the rarity I think the
> current one in sustainable.
What if we clear vm_private_data? And maybe do a pr_warn_ratelimited()
so that userspace gets some form of notification that forking an enclave
failed. A NULL encl is easy to check in the fault handler and any where
else we consume vmas.
>
> >
> > > + goto out;
> > > + }
> > > +
> > > + spin_lock(&encl->mm_lock);
> > > + mm->encl = encl;
> > > + mm->mm = vma->vm_mm;
> > > + list_add(&mm->list, &encl->mm_list);
> > > + kref_init(&mm->refcount);
> >
> > Not that it truly matters, but list_add() is the only thing that needs
> > to be protected with the spinlock, everything else can be done ahead of
> > time.
>
> True :-)
>
> >
> > > + spin_unlock(&encl->mm_lock);
> > > + } else {
> > > + mmdrop(mm->mm);
> > > + }
> > > +
> > > +out:
> > > + kref_get(&encl->refcount);
> > > +}
> > > +
> > > +static void sgx_vma_close(struct vm_area_struct *vma)
> > > +{
> > > + struct sgx_encl *encl = vma->vm_private_data;
> > > + struct sgx_encl_mm *mm;
> > > +
> > > + if (!encl)
> > > + return;
> > > +
> > > + mm = sgx_encl_get_mm(encl, vma->vm_mm);
> >
> > Isn't this unnecessary? sgx_vma_open() had to have been called on this
> > VMA, otherwise we wouldn't be here.
>
> Not in the case when allocation fails in vma_open.
Ah, I see the flow. If we do keep the enclave killing behavior then I
think it'd make sense to let this be handled by checking SGX_ENCL_DEAD.
But AFAICT things will "just work" if we nullify vm_private_data.
