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[xen master] xen/iommu: x86: Clear the root page-table before freeing the page-tables

commit 9bd9695a8bc72a86b98c0683736d2310838558fe
Author:     Julien Grall <jgrall@xxxxxxxxxx>
AuthorDate: Fri Feb 26 10:56:40 2021 +0000
Commit:     Julien Grall <jgrall@xxxxxxxxxx>
CommitDate: Tue Mar 2 09:54:43 2021 +0000

    xen/iommu: x86: Clear the root page-table before freeing the page-tables
    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.
    Take the opportunity to add an ASSERT() in arch_iommu_domain_destroy()
    to check if we freed all the IOMMU page tables.
    Fixes: 3eef6d07d722 ("x86/iommu: convert VT-d code to use new page table 
    Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
    Release-Acked-by: Ian Jackson <iwj@xxxxxxxxxxxxxx>
 xen/drivers/passthrough/amd/pci_amd_iommu.c | 12 +++++++++++-
 xen/drivers/passthrough/vtd/iommu.c         | 12 +++++++++++-
 xen/drivers/passthrough/x86/iommu.c         | 13 +++++++++++++
 xen/include/xen/iommu.h                     |  1 +
 4 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/xen/drivers/passthrough/amd/pci_amd_iommu.c 
index 42b5a5a9be..085fe2f577 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 
     return reassign_device(pdev->domain, d, devfn, pdev);
+static void amd_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 = amd_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 
index b549a71530..475efb3be3 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)
-    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,
@@ -2731,6 +2740,7 @@ 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 
index ad19b7dd46..b90bb31bfe 100644
--- a/xen/drivers/passthrough/x86/iommu.c
+++ b/xen/drivers/passthrough/x86/iommu.c
@@ -149,6 +149,13 @@ int arch_iommu_domain_init(struct domain *d)
 void arch_iommu_domain_destroy(struct domain *d)
+    /*
+     * There should be not page-tables left allocated by the time the
+     * domain is destroyed. Note that arch_iommu_domain_destroy() is
+     * called unconditionally, so pgtables may be uninitialized.
+     */
+    ASSERT(!dom_iommu(d)->platform_ops ||
+           page_list_empty(&dom_iommu(d)->arch.pgtables.list));
 static bool __hwdom_init hwdom_iommu_map(const struct domain *d,
@@ -273,6 +280,12 @@ int iommu_free_pgtables(struct domain *d)
     /* After this barrier, no new IOMMU mappings can be inserted. */
+    /*
+     * 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)) )
diff --git a/xen/include/xen/iommu.h b/xen/include/xen/iommu.h
index 863a68fe16..d59ed7cbad 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);
generated by git-patchbot for /home/xen/git/xen.git#master



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