[Xen-changelog] [xen stable-4.11] x86/mm: Put the gfn on all paths after get_gfn_query()

[patchbot@xxxxxxx]

commit eb6830a1c8347d0c5e33571f93cbd2d79330798d
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Tue Nov 20 15:32:34 2018 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Nov 20 15:32:34 2018 +0100

    x86/mm: Put the gfn on all paths after get_gfn_query()
    
    c/s 7867181b2 "x86/PoD: correctly handle non-order-0 decrease-reservation
    requests" introduced an early exit in guest_remove_page() for unexpected p2m
    types.  However, get_gfn_query() internally takes the p2m lock, and must be
    matched with a put_gfn() call later.
    
    Fix the erroneous comment beside the declaration of get_gfn_query().
    
    This is XSA-277.
    
    Reported-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    master commit: d80988cfc04ee608bee722448e7c3bc8347ec04c
    master date: 2018-11-20 14:58:10 +0100
---
 xen/common/memory.c       | 4 ++++
 xen/include/asm-x86/p2m.h | 5 +----
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/xen/common/memory.c b/xen/common/memory.c
index 75010b78a5..4fb7962c79 100644
--- a/xen/common/memory.c
+++ b/xen/common/memory.c
@@ -303,7 +303,11 @@ int guest_remove_page(struct domain *d, unsigned long gmfn)
 #ifdef CONFIG_X86
     mfn = get_gfn_query(d, gmfn, &p2mt);
     if ( unlikely(p2mt == p2m_invalid) || unlikely(p2mt == p2m_mmio_dm) )
+    {
+        put_gfn(d, gmfn);
+
         return -ENOENT;
+    }
 
     if ( unlikely(p2m_is_paging(p2mt)) )
     {
diff --git a/xen/include/asm-x86/p2m.h b/xen/include/asm-x86/p2m.h
index d4b3cfcb6e..3f41deaeea 100644
--- a/xen/include/asm-x86/p2m.h
+++ b/xen/include/asm-x86/p2m.h
@@ -432,10 +432,7 @@ static inline mfn_t __nonnull(3) get_gfn_type(
     return get_gfn_type_access(p2m_get_hostp2m(d), gfn, t, &a, q, NULL);
 }
 
-/* Syntactic sugar: most callers will use one of these. 
- * N.B. get_gfn_query() is the _only_ one guaranteed not to take the
- * p2m lock; none of the others can be called with the p2m or paging
- * lock held. */
+/* Syntactic sugar: most callers will use one of these. */
 #define get_gfn(d, g, t)         get_gfn_type((d), (g), (t), P2M_ALLOC)
 #define get_gfn_query(d, g, t)   get_gfn_type((d), (g), (t), 0)
 #define get_gfn_unshare(d, g, t) get_gfn_type((d), (g), (t), \
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.11

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