[Xen-devel] [PATCH v2 2/2] xen/x86: hap: Clean-up and harden hap_enable()

[Julien Grall <julien@xen.org>]

From: Julien Grall <jgrall@amazon.com>

Unlike shadow_enable(), hap_enable() can only be called once during
domain creation and with the mode equal to mode equal to
PG_external | PG_translate | PG_refcounts.

If it were called twice, then we might have something interesting
problem as the p2m tables would be re-allocated (and therefore all the
mappings would be lost).

Add code to sanity check the mode and that the function is only called
once. Take the opportunity to an if checking that PG_translate is set.

Signed-off-by: Julien Grall <jgrall@amazon.com>

---

It is not entirely clear when PG_translate was enforced.

I keep the check != 0 because this is consistent with the rest of the
file. If we want to omit comparison against 0, then this should be in a
separate patches converting the file.

    Changes in v2:
        - Fix typoes in the commit message
        - Use -EEXIST instead of -EINVAL
---
 xen/arch/x86/mm/hap/hap.c | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/xen/arch/x86/mm/hap/hap.c b/xen/arch/x86/mm/hap/hap.c
index 31362a31b6..4974bd13d4 100644
--- a/xen/arch/x86/mm/hap/hap.c
+++ b/xen/arch/x86/mm/hap/hap.c
@@ -445,6 +445,13 @@ int hap_enable(struct domain *d, u32 mode)
     unsigned int i;
     int rv = 0;
 
+    if ( mode != (PG_external | PG_translate | PG_refcounts) )
+        return -EINVAL;
+
+    /* The function can only be called once */
+    if ( d->arch.paging.mode != 0 )
+        return -EEXIST;
+
     domain_pause(d);
 
     old_pages = d->arch.paging.hap.total_pages;
@@ -465,13 +472,10 @@ int hap_enable(struct domain *d, u32 mode)
     d->arch.paging.alloc_page = hap_alloc_p2m_page;
     d->arch.paging.free_page = hap_free_p2m_page;
 
-    /* allocate P2m table */
-    if ( mode & PG_translate )
-    {
-        rv = p2m_alloc_table(p2m_get_hostp2m(d));
-        if ( rv != 0 )
-            goto out;
-    }
+    /* allocate P2M table */
+    rv = p2m_alloc_table(p2m_get_hostp2m(d));
+    if ( rv != 0 )
+        goto out;
 
     for ( i = 0; i < MAX_NESTEDP2M; i++ )
     {
-- 
2.17.1


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