[Xen-devel] [PATCH 2/4] hvm/dmop: Implement copy_{to, from}_guest_buf() in terms of raw accessors

[<jennifer.herbert@xxxxxxxxxx>]

From: Jennifer Herbert <Jennifer.Herbert@xxxxxxxxxx>

This also allows the usual cases to be simplified, by omitting an unnecessary
buf parameters, and because the macros can appropriately size the object.

This makes copying to or from a buf that isn't big enough an error.
If the buffer isnt big enough, trying to carry on regardless
can only cause trouble later on.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Signed-off-by: Jennifer Herbert <Jennifer.Herbert@xxxxxxxxxx>
--
CC: Paul Durrant <paul.durrant@xxxxxxxxxx>
CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Julien Grall <julien.grall@xxxxxxx>
---
 xen/arch/x86/hvm/dm.c | 47 +++++++++++++++++++++++++++++------------------
 1 file changed, 29 insertions(+), 18 deletions(-)

diff --git a/xen/arch/x86/hvm/dm.c b/xen/arch/x86/hvm/dm.c
index fb4bcec..3607ddb 100644
--- a/xen/arch/x86/hvm/dm.c
+++ b/xen/arch/x86/hvm/dm.c
@@ -32,36 +32,47 @@ struct dmop_args {
     struct xen_dm_op_buf buf[2];
 };
 
-static bool copy_buf_from_guest(const xen_dm_op_buf_t bufs[],
-                                unsigned int nr_bufs, void *dst,
-                                unsigned int idx, size_t dst_size)
+static bool _raw_copy_from_guest_buf(void *dst,
+                                     const struct dmop_args *args,
+                                     unsigned int buf_idx,
+                                     size_t dst_bytes)
 {
-    size_t size;
+    size_t buf_bytes;
 
-    if ( idx >= nr_bufs )
+    if ( buf_idx >= args->nr_bufs )
         return false;
 
-    memset(dst, 0, dst_size);
+    buf_bytes =  args->buf[buf_idx].size;
 
-    size = min_t(size_t, dst_size, bufs[idx].size);
+    if ( dst_bytes > buf_bytes )
+        return false;
 
-    return !copy_from_guest(dst, bufs[idx].h, size);
+    return !copy_from_guest(dst, args->buf[buf_idx].h, buf_bytes);
 }
 
-static bool copy_buf_to_guest(const xen_dm_op_buf_t bufs[],
-                              unsigned int nr_bufs, unsigned int idx,
-                              const void *src, size_t src_size)
+static bool _raw_copy_to_guest_buf(struct dmop_args *args,
+                                   unsigned int buf_idx,
+                                   const void *src, size_t src_bytes)
 {
-    size_t size;
+    size_t buf_bytes;
 
-    if ( idx >= nr_bufs )
+    if ( buf_idx >= args->nr_bufs )
         return false;
 
-    size = min_t(size_t, bufs[idx].size, src_size);
+    buf_bytes = args->buf[buf_idx].size;
+
+    if ( src_bytes > buf_bytes )
+        return false;
 
-    return !copy_to_guest(bufs[idx].h, src, size);
+    return !copy_to_guest(args->buf[buf_idx].h, src, buf_bytes);
 }
 
+#define copy_from_guest_buf(dst, args, buf_idx) \
+    _raw_copy_from_guest_buf(dst, args, buf_idx, sizeof(*(dst)))
+
+#define copy_to_guest_buf(args, buf_idx, src) \
+    _raw_copy_to_guest_buf(args, buf_idx, src, sizeof(*(src)))
+
 static int track_dirty_vram(struct domain *d, xen_pfn_t first_pfn,
                             unsigned int nr, struct xen_dm_op_buf *buf)
 {
@@ -312,7 +323,7 @@ static int dm_op(struct dmop_args *op_args)
     if ( rc )
         goto out;
 
-    if ( !copy_buf_from_guest(&op_args->buf[0], op_args->nr_bufs, &op, 0, 
sizeof(op)) )
+    if ( !copy_from_guest_buf(&op, op_args, 0) );
     {
         rc = -EFAULT;
         goto out;
@@ -568,8 +579,8 @@ static int dm_op(struct dmop_args *op_args)
     }
 
     if ( (!rc || rc == -ERESTART) &&
-         !const_op &&
-         !copy_buf_to_guest(&op_args->buf[0], op_args->nr_bufs, 0, &op, 
sizeof(op)) )
+         !const_op && !copy_to_guest_buf(op_args, 0, &op) )
+
         rc = -EFAULT;
 
  out:
-- 
2.1.4


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