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envelope-from=alxndr@bu.edu; helo=NAM11-BN8-obe.outbound.protection.outlook.com X-Spam_score_int: -1 X-Spam_score: -0.2 X-Spam_bar: / X-Spam_report: (-0.2 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, HK_RANDOM_ENVFROM=0.89, HK_RANDOM_FROM=0.999, MSGID_FROM_MTA_HEADER=0.001, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Alexander Bulekov , =?UTF-8?q?Philippe=20Mathieu-Daud=C3=A9?= , Darren Kenny Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 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 Reviewed-by: Darren Kenny Reviewed-by: Philippe Mathieu-Daudé --- tests/qtest/fuzz/generic_fuzz.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) diff --git a/tests/qtest/fuzz/generic_fuzz.c b/tests/qtest/fuzz/generic_fuzz.c index 6c67522717..0ea47298b7 100644 --- a/tests/qtest/fuzz/generic_fuzz.c +++ b/tests/qtest/fuzz/generic_fuzz.c @@ -240,10 +240,17 @@ void fuzz_dma_read_cb(size_t addr, size_t len, MemoryRegion *mr) 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) { /* -- 2.30.2