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Fix subtle integer overflow bug in memory API 

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 <david@gibson.dropbear.id.au>
Signed-off-by: Avi Kivity <avi@redhat.com>
This commit is contained in:
David Gibson 2011-09-14 17:02:49 +10:00 committed by Avi Kivity
parent 44520db10b
commit d2963631dd
1 changed files with 2 additions and 2 deletions
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4
memory.c
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@ -55,8 +55,8 @@ static AddrRange addrrange_shift(AddrRange range, int64_t delta)
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)