[xen stable-4.13] x86/p2m: add option to skip root pagetable removal in p2m_teardown()

[patchbot@xxxxxxx]

commit 763f965d04c5eb01890f697aaaaa9120d552672a
Author:     Roger Pau Monné <roger.pau@xxxxxxxxxx>
AuthorDate: Tue Oct 11 15:48:01 2022 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Oct 11 15:48:01 2022 +0200

    x86/p2m: add option to skip root pagetable removal in p2m_teardown()
    
    Add a new parameter to p2m_teardown() in order to select whether the
    root page table should also be freed.  Note that all users are
    adjusted to pass the parameter to remove the root page tables, so
    behavior is not modified.
    
    No functional change intended.
    
    This is part of CVE-2022-33746 / XSA-410.
    
    Suggested-by: Julien Grall <julien@xxxxxxx>
    Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    Acked-by: Tim Deegan <tim@xxxxxxx>
    master commit: 1df52a270225527ae27bfa2fc40347bf93b78357
    master date: 2022-10-11 14:21:23 +0200
---
 xen/arch/x86/mm/hap/hap.c       |  6 +++---
 xen/arch/x86/mm/p2m.c           | 20 ++++++++++++++++----
 xen/arch/x86/mm/shadow/common.c |  4 ++--
 xen/include/asm-x86/p2m.h       |  2 +-
 4 files changed, 22 insertions(+), 10 deletions(-)

diff --git a/xen/arch/x86/mm/hap/hap.c b/xen/arch/x86/mm/hap/hap.c
index 9aac006d65..c2d425a4b1 100644
--- a/xen/arch/x86/mm/hap/hap.c
+++ b/xen/arch/x86/mm/hap/hap.c
@@ -521,18 +521,18 @@ void hap_final_teardown(struct domain *d)
         }
 
         for ( i = 0; i < MAX_ALTP2M; i++ )
-            p2m_teardown(d->arch.altp2m_p2m[i]);
+            p2m_teardown(d->arch.altp2m_p2m[i], true);
     }
 
     /* Destroy nestedp2m's first */
     for (i = 0; i < MAX_NESTEDP2M; i++) {
-        p2m_teardown(d->arch.nested_p2m[i]);
+        p2m_teardown(d->arch.nested_p2m[i], true);
     }
 
     if ( d->arch.paging.hap.total_pages != 0 )
         hap_teardown(d, NULL);
 
-    p2m_teardown(p2m_get_hostp2m(d));
+    p2m_teardown(p2m_get_hostp2m(d), true);
     /* Free any memory that the p2m teardown released */
     paging_lock(d);
     hap_set_allocation(d, 0, NULL);
diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
index 91f7b7760c..859edfc95b 100644
--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -737,11 +737,11 @@ int p2m_alloc_table(struct p2m_domain *p2m)
  * hvm fixme: when adding support for pvh non-hardware domains, this path must
  * cleanup any foreign p2m types (release refcnts on them).
  */
-void p2m_teardown(struct p2m_domain *p2m)
+void p2m_teardown(struct p2m_domain *p2m, bool remove_root)
 /* Return all the p2m pages to Xen.
  * We know we don't have any extra mappings to these pages */
 {
-    struct page_info *pg;
+    struct page_info *pg, *root_pg = NULL;
     struct domain *d;
 
     if (p2m == NULL)
@@ -751,10 +751,22 @@ void p2m_teardown(struct p2m_domain *p2m)
 
     p2m_lock(p2m);
     ASSERT(atomic_read(&d->shr_pages) == 0);
-    p2m->phys_table = pagetable_null();
+
+    if ( remove_root )
+        p2m->phys_table = pagetable_null();
+    else if ( !pagetable_is_null(p2m->phys_table) )
+    {
+        root_pg = pagetable_get_page(p2m->phys_table);
+        clear_domain_page(pagetable_get_mfn(p2m->phys_table));
+    }
 
     while ( (pg = page_list_remove_head(&p2m->pages)) )
-        d->arch.paging.free_page(d, pg);
+        if ( pg != root_pg )
+            d->arch.paging.free_page(d, pg);
+
+    if ( root_pg )
+        page_list_add(root_pg, &p2m->pages);
+
     p2m_unlock(p2m);
 }
 
diff --git a/xen/arch/x86/mm/shadow/common.c b/xen/arch/x86/mm/shadow/common.c
index dd8d9240ea..68d2679c7a 100644
--- a/xen/arch/x86/mm/shadow/common.c
+++ b/xen/arch/x86/mm/shadow/common.c
@@ -2684,7 +2684,7 @@ int shadow_enable(struct domain *d, u32 mode)
     paging_unlock(d);
  out_unlocked:
     if ( rv != 0 && !pagetable_is_null(p2m_get_pagetable(p2m)) )
-        p2m_teardown(p2m);
+        p2m_teardown(p2m, true);
     if ( rv != 0 && pg != NULL )
     {
         pg->count_info &= ~PGC_count_mask;
@@ -2835,7 +2835,7 @@ void shadow_final_teardown(struct domain *d)
         shadow_teardown(d, NULL);
 
     /* It is now safe to pull down the p2m map. */
-    p2m_teardown(p2m_get_hostp2m(d));
+    p2m_teardown(p2m_get_hostp2m(d), true);
     /* Free any shadow memory that the p2m teardown released */
     paging_lock(d);
     shadow_set_allocation(d, 0, NULL);
diff --git a/xen/include/asm-x86/p2m.h b/xen/include/asm-x86/p2m.h
index 807dc4b1a9..cab4ca60fa 100644
--- a/xen/include/asm-x86/p2m.h
+++ b/xen/include/asm-x86/p2m.h
@@ -599,7 +599,7 @@ int p2m_init(struct domain *d);
 int p2m_alloc_table(struct p2m_domain *p2m);
 
 /* Return all the p2m resources to Xen. */
-void p2m_teardown(struct p2m_domain *p2m);
+void p2m_teardown(struct p2m_domain *p2m, bool remove_root);
 void p2m_final_teardown(struct domain *d);
 
 /* Add a page to a domain's p2m table */
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.13