[xen staging] xen/iommu: Check if the IOMMU was initialized before tearing down

[patchbot@xxxxxxx]

commit d670ef3401b91d04c58d72cd8ce5579b4fa900d8
Author:     Julien Grall <jgrall@xxxxxxxxxx>
AuthorDate: Thu Dec 17 12:27:21 2020 +0000
Commit:     Julien Grall <jgrall@xxxxxxxxxx>
CommitDate: Wed Feb 17 11:30:05 2021 +0000

    xen/iommu: Check if the IOMMU was initialized before tearing down
    
    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>
    Reviewed-by: Paul Durrant <paul@xxxxxxx>
---
 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 2358b6eb09..879d238bcd 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);
 }
 
--
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