[for-4.15][PATCH v2 2/5] xen/iommu: Check if the IOMMU was initialized before tearing down

[Julien Grall <julien@xxxxxxx>]

From: Julien Grall <jgrall@xxxxxxxxxx>

is_iommu_enabled() will return true even if the IOMMU has not been
initialized (e.g. the ops are not set).

In the case of an early failure in arch_domain_init(), the function
iommu_destroy_domain() will be called even if the IOMMU is not
initialized.

This will result to dereference the ops which will be NULL and an host
crash.

Fix the issue by checking that ops has been set before accessing it.

Fixes: 71e617a6b8f6 ("use is_iommu_enabled() where appropriate...")
Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>

---
    Changes in v2:
        - Move the check in iommu_teardown() so we don't rely on
        arch_iommu_domain_init() to clean-up its allocation on failure.
        - Fix typo in the commit message
---
 xen/drivers/passthrough/iommu.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/xen/drivers/passthrough/iommu.c b/xen/drivers/passthrough/iommu.c
index 2358b6eb09f4..879d238bcd31 100644
--- a/xen/drivers/passthrough/iommu.c
+++ b/xen/drivers/passthrough/iommu.c
@@ -221,6 +221,13 @@ static void iommu_teardown(struct domain *d)
 {
     struct domain_iommu *hd = dom_iommu(d);
 
+    /*
+     * During early domain creation failure, we may reach here with the
+     * ops not yet initialized.
+     */
+    if ( !hd->platform_ops )
+        return;
+
     iommu_vcall(hd->platform_ops, teardown, d);
 }
 
-- 
2.17.1