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[Qemu-devel] [PATCH] Fix subtle integer overflow bug in memory API

From: David Gibson
Subject: [Qemu-devel] [PATCH] Fix subtle integer overflow bug in memory API
Date: Wed, 14 Sep 2011 17:02:49 +1000

It is quite common to have a MemoryRegion with size of INT64_MAX.
When processing alias regions in render_memory_region() it's quite
easy to find a case where it will construct a temporary AddrRange with
a non-zero start, and size still of INT64_MAX.  When means attempting
to compute the end of such a range as start + size will result in
signed integer overflow.

This integer overflow means that addrrange_intersects() can
incorrectly report regions as not intersecting when they do.  For
example consider the case of address ranges {0x10000000000,
0x7fffffffffffffff} and {0x10010000000, 0x10000000} where the second
is in fact included completely in the first.

This patch rearranges addrrange_intersects() to avoid the integer
overflow, correcting this behaviour.

Signed-off-by: David Gibson <address@hidden>
 memory.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/memory.c b/memory.c
index 57f0fa4..101b67c 100644
--- a/memory.c
+++ b/memory.c
@@ -55,8 +55,8 @@ static AddrRange addrrange_shift(AddrRange range, int64_t 
 static bool addrrange_intersects(AddrRange r1, AddrRange r2)
-    return (r1.start >= r2.start && r1.start < r2.start + r2.size)
-        || (r2.start >= r1.start && r2.start < r1.start + r1.size);
+    return (r1.start >= r2.start && (r1.start - r2.start) < r2.size)
+        || (r2.start >= r1.start && (r2.start - r1.start) < r1.size);
 static AddrRange addrrange_intersection(AddrRange r1, AddrRange r2)

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