From: Julien Grall <jgr...@amazon.com>
The new per-domain IOMMU page-table allocator will now free the
page-tables when domain's resources are relinquished. However, the
per-domain IOMMU structure will still contain a dangling pointer to
the root page-table.
Xen may access the IOMMU page-tables afterwards at least in the case of
PV domain:
(XEN) Xen call trace:
(XEN) [<ffff82d04025b4b2>] R iommu.c#addr_to_dma_page_maddr+0x12e/0x1d8
(XEN) [<ffff82d04025b695>] F iommu.c#intel_iommu_unmap_page+0x5d/0xf8
(XEN) [<ffff82d0402695f3>] F iommu_unmap+0x9c/0x129
(XEN) [<ffff82d0402696a6>] F iommu_legacy_unmap+0x26/0x63
(XEN) [<ffff82d04033c5c7>] F mm.c#cleanup_page_mappings+0x139/0x144
(XEN) [<ffff82d04033c61d>] F put_page+0x4b/0xb3
(XEN) [<ffff82d04033c87f>] F put_page_from_l1e+0x136/0x13b
(XEN) [<ffff82d04033cada>] F devalidate_page+0x256/0x8dc
(XEN) [<ffff82d04033d396>] F mm.c#_put_page_type+0x236/0x47e
(XEN) [<ffff82d04033d64d>] F mm.c#put_pt_page+0x6f/0x80
(XEN) [<ffff82d04033d8d6>] F mm.c#put_page_from_l2e+0x8a/0xcf
(XEN) [<ffff82d04033cc27>] F devalidate_page+0x3a3/0x8dc
(XEN) [<ffff82d04033d396>] F mm.c#_put_page_type+0x236/0x47e
(XEN) [<ffff82d04033d64d>] F mm.c#put_pt_page+0x6f/0x80
(XEN) [<ffff82d04033d807>] F mm.c#put_page_from_l3e+0x8a/0xcf
(XEN) [<ffff82d04033cdf0>] F devalidate_page+0x56c/0x8dc
(XEN) [<ffff82d04033d396>] F mm.c#_put_page_type+0x236/0x47e
(XEN) [<ffff82d04033d64d>] F mm.c#put_pt_page+0x6f/0x80
(XEN) [<ffff82d04033d6c7>] F mm.c#put_page_from_l4e+0x69/0x6d
(XEN) [<ffff82d04033cf24>] F devalidate_page+0x6a0/0x8dc
(XEN) [<ffff82d04033d396>] F mm.c#_put_page_type+0x236/0x47e
(XEN) [<ffff82d04033d92e>] F put_page_type_preemptible+0x13/0x15
(XEN) [<ffff82d04032598a>] F domain.c#relinquish_memory+0x1ff/0x4e9
(XEN) [<ffff82d0403295f2>] F domain_relinquish_resources+0x2b6/0x36a
(XEN) [<ffff82d040205cdf>] F domain_kill+0xb8/0x141
(XEN) [<ffff82d040236cac>] F do_domctl+0xb6f/0x18e5
(XEN) [<ffff82d04031d098>] F pv_hypercall+0x2f0/0x55f
(XEN) [<ffff82d04039b432>] F lstar_enter+0x112/0x120
This will result to a use after-free and possibly an host crash or
memory corruption.
It would not be possible to free the page-tables further down in
domain_relinquish_resources() because cleanup_page_mappings() will only
be called when the last reference on the page dropped. This may happen
much later if another domain still hold a reference.
After all the PCI devices have been de-assigned, nobody should use the
IOMMU page-tables and it is therefore pointless to try to modify them.
So we can simply clear any reference to the root page-table in the
per-domain IOMMU structure. This requires to introduce a new callback of
the method will depend on the IOMMU driver used.
Fixes: 3eef6d07d722 ("x86/iommu: convert VT-d code to use new page table
allocator")
Signed-off-by: Julien Grall <jgr...@amazon.com>
---
Changes in v3:
- Move the patch earlier in the series
- Reword the commit message
Changes in v2:
- Introduce clear_root_pgtable()
- Move the patch later in the series
---
xen/drivers/passthrough/amd/pci_amd_iommu.c | 12 +++++++++++-
xen/drivers/passthrough/vtd/iommu.c | 12 +++++++++++-
xen/drivers/passthrough/x86/iommu.c | 9 +++++++++
xen/include/xen/iommu.h | 1 +
4 files changed, 32 insertions(+), 2 deletions(-)
diff --git a/xen/drivers/passthrough/amd/pci_amd_iommu.c
b/xen/drivers/passthrough/amd/pci_amd_iommu.c
index 42b5a5a9bec4..81add0ba26b4 100644
--- a/xen/drivers/passthrough/amd/pci_amd_iommu.c
+++ b/xen/drivers/passthrough/amd/pci_amd_iommu.c
@@ -381,9 +381,18 @@ static int amd_iommu_assign_device(struct domain *d, u8
devfn,
return reassign_device(pdev->domain, d, devfn, pdev);
}
+static void iommu_clear_root_pgtable(struct domain *d)
+{
+ struct domain_iommu *hd = dom_iommu(d);
+
+ spin_lock(&hd->arch.mapping_lock);
+ hd->arch.amd.root_table = NULL;
+ spin_unlock(&hd->arch.mapping_lock);
+}
+
static void amd_iommu_domain_destroy(struct domain *d)
{
- dom_iommu(d)->arch.amd.root_table = NULL;
+ ASSERT(!dom_iommu(d)->arch.amd.root_table);
}
static int amd_iommu_add_device(u8 devfn, struct pci_dev *pdev)
@@ -565,6 +574,7 @@ static const struct iommu_ops __initconstrel _iommu_ops = {
.remove_device = amd_iommu_remove_device,
.assign_device = amd_iommu_assign_device,
.teardown = amd_iommu_domain_destroy,
+ .clear_root_pgtable = iommu_clear_root_pgtable,
.map_page = amd_iommu_map_page,
.unmap_page = amd_iommu_unmap_page,
.iotlb_flush = amd_iommu_flush_iotlb_pages,
diff --git a/xen/drivers/passthrough/vtd/iommu.c
b/xen/drivers/passthrough/vtd/iommu.c
index d136fe36883b..e1871f6c2bc1 100644
--- a/xen/drivers/passthrough/vtd/iommu.c
+++ b/xen/drivers/passthrough/vtd/iommu.c
@@ -1726,6 +1726,15 @@ out:
return ret;
}
+static void iommu_clear_root_pgtable(struct domain *d)
+{
+ struct domain_iommu *hd = dom_iommu(d);
+
+ spin_lock(&hd->arch.mapping_lock);
+ hd->arch.vtd.pgd_maddr = 0;
+ spin_unlock(&hd->arch.mapping_lock);
+}
+
static void iommu_domain_teardown(struct domain *d)
{
struct domain_iommu *hd = dom_iommu(d);
@@ -1740,7 +1749,7 @@ static void iommu_domain_teardown(struct domain *d)
xfree(mrmrr);
}
- hd->arch.vtd.pgd_maddr = 0;
+ ASSERT(!hd->arch.vtd.pgd_maddr);
}
static int __must_check intel_iommu_map_page(struct domain *d, dfn_t dfn,
@@ -2719,6 +2728,7 @@ static struct iommu_ops __initdata vtd_ops = {
.remove_device = intel_iommu_remove_device,
.assign_device = intel_iommu_assign_device,
.teardown = iommu_domain_teardown,
+ .clear_root_pgtable = iommu_clear_root_pgtable,
.map_page = intel_iommu_map_page,
.unmap_page = intel_iommu_unmap_page,
.lookup_page = intel_iommu_lookup_page,
diff --git a/xen/drivers/passthrough/x86/iommu.c
b/xen/drivers/passthrough/x86/iommu.c
index cea1032b3d02..f54fc8093f18 100644
--- a/xen/drivers/passthrough/x86/iommu.c
+++ b/xen/drivers/passthrough/x86/iommu.c
@@ -267,6 +267,15 @@ int iommu_free_pgtables(struct domain *d)
struct page_info *pg;
unsigned int done = 0;
+ if ( !is_iommu_enabled(d) )
+ return 0;
+
+ /*
+ * Pages will be moved to the free list below. So we want to
+ * clear the root page-table to avoid any potential use after-free.
+ */
+ hd->platform_ops->clear_root_pgtable(d);
+
while ( (pg = page_list_remove_head(&hd->arch.pgtables.list)) )
{
free_domheap_page(pg);
diff --git a/xen/include/xen/iommu.h b/xen/include/xen/iommu.h
index 863a68fe1622..d59ed7cbad43 100644
--- a/xen/include/xen/iommu.h
+++ b/xen/include/xen/iommu.h
@@ -272,6 +272,7 @@ struct iommu_ops {
int (*adjust_irq_affinities)(void);
void (*sync_cache)(const void *addr, unsigned int size);
+ void (*clear_root_pgtable)(struct domain *d);
#endif /* CONFIG_X86 */
int __must_check (*suspend)(void);
--
2.17.1
