The code mistakenly relied on address_space_translate to store the
length remaining until the next memory-region. We care about this
because when there is RAM or sparse-memory neighboring on an MMIO
region, we should only write up to the border, to prevent inadvertently
invoking MMIO handlers within the DMA callback.
However address_space_translate_internal only stores the length until
the end of the MemoryRegion if memory_region_is_ram(mr). Otherwise
the *len is left unmodified. This caused some false-positive issues,
where the fuzzer found a way to perform a nested MMIO write through a
DMA callback on an [address, length] that started within sparse memory
and spanned some device MMIO regions.
To fix this, write to sparse memory in small chunks of
memory_access_size (similar to the underlying address_space_write code),
which will prevent accidentally hitting MMIO handlers through large
writes.
Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
addr, &addr1, &l, true,
MEMTXATTRS_UNSPECIFIED);
- if (!(memory_region_is_ram(mr1) ||
- memory_region_is_romd(mr1)) && mr1 != sparse_mem_mr) {
+ /*
+ * If mr1 isn't RAM, address_space_translate doesn't update l. Use
+ * memory_access_size to identify the number of bytes that it is safe
+ * to write without accidentally writing to another MemoryRegion.
+ */
+ if (!memory_region_is_ram(mr1)) {
l = memory_access_size(mr1, l, addr1);
- } else {
+ }
+ if (memory_region_is_ram(mr1) ||
+ memory_region_is_romd(mr1) ||
+ mr1 == sparse_mem_mr) {
/* ROM/RAM case */
if (qtest_log_enabled) {
/*