blob: 0549216dcf259e01ab615ed46dd655bb869af49e (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
|
xen/blkif: Avoid double access to src->nr_segments
src is stored in shared memory and src->nr_segments is dereferenced
twice at the end of the function. If a compiler decides to compile this
into two separate memory accesses then the size limitation could be
bypassed.
Fix it by removing the double access to src->nr_segments.
This is part of XSA-155.
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
diff --git a/hw/block/xen_blkif.h b/hw/block/xen_blkif.h
index 711b692..9e71e00 100644
--- a/hw/block/xen_blkif.h
+++ b/hw/block/xen_blkif.h
@@ -85,8 +85,10 @@ static inline void blkif_get_x86_32_req(blkif_request_t *dst, blkif_x86_32_reque
d->nr_sectors = s->nr_sectors;
return;
}
- if (n > src->nr_segments)
- n = src->nr_segments;
+ /* prevent the compiler from optimizing the code and using src->nr_segments instead */
+ barrier();
+ if (n > dst->nr_segments)
+ n = dst->nr_segments;
for (i = 0; i < n; i++)
dst->seg[i] = src->seg[i];
}
@@ -106,8 +108,10 @@ static inline void blkif_get_x86_64_req(blkif_request_t *dst, blkif_x86_64_reque
d->nr_sectors = s->nr_sectors;
return;
}
- if (n > src->nr_segments)
- n = src->nr_segments;
+ /* prevent the compiler from optimizing the code and using src->nr_segments instead */
+ barrier();
+ if (n > dst->nr_segments)
+ n = dst->nr_segments;
for (i = 0; i < n; i++)
dst->seg[i] = src->seg[i];
}
|
