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exec: fix incorrect assumptions in memory_access_size

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access_size_min can be 1 because erroneous accesses must not crash
QEMU, they should trigger exceptions in the guest or just return
garbage (depending on the CPU).  I am not sure I understand the
comment: placing a 4-byte field at the last byte of a region
makes no sense (unless impl.unaligned is true), and that is
why memory.c:access_with_adjusted_size does not bother with
minimums larger than the remaining length.

access_size_max can be mr->ops->valid.max_access_size because memory.c
can and will still break accesses bigger than
mr->ops->impl.max_access_size.

Reported-by: Markus Armbruster <armbru@redhat.com>
Tested-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2013-07-17 13:17:41 +02:00
parent 9b8c692435
commit e1622f4b15
1 changed files with 1 additions and 8 deletions
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9
exec.c
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@ -1898,14 +1898,10 @@ static inline bool memory_access_is_direct(MemoryRegion *mr, bool is_write)
static int memory_access_size(MemoryRegion *mr, unsigned l, hwaddr addr)
{
unsigned access_size_min = mr->ops->impl.min_access_size;
unsigned access_size_max = mr->ops->impl.max_access_size;
unsigned access_size_max = mr->ops->valid.max_access_size;
/* Regions are assumed to support 1-4 byte accesses unless
otherwise specified. */
if (access_size_min == 0) {
access_size_min = 1;
}
if (access_size_max == 0) {
access_size_max = 4;
}
@ -1922,9 +1918,6 @@ static int memory_access_size(MemoryRegion *mr, unsigned l, hwaddr addr)
if (l > access_size_max) {
l = access_size_max;
}
/* ??? The users of this function are wrong, not supporting minimums larger
than the remaining length. C.f. memory.c:access_with_adjusted_size. */
assert(l >= access_size_min);
return l;
}