On 28/11/22 16:16, Stefan Hajnoczi wrote:
On Mon, 28 Nov 2022 at 08:53, Philippe Mathieu-Daudé <phi...@linaro.org> wrote:
Have qxl_get_check_slot_offset() return false if the requested
buffer size does not fit within the slot memory region.
Similarly qxl_phys2virt() now returns NULL in such case, and
qxl_dirty_one_surface() aborts.
This avoids buffer overrun in the host pointer returned by
memory_region_get_ram_ptr().
Fixes: CVE-2022-4144 (out-of-bounds read)
Reported-by: Wenxu Yin (@awxylitol)
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1336
Signed-off-by: Philippe Mathieu-Daudé <phi...@linaro.org>
---
hw/display/qxl.c | 22 ++++++++++++++++++----
hw/display/qxl.h | 2 +-
2 files changed, 19 insertions(+), 5 deletions(-)
diff --git a/hw/display/qxl.c b/hw/display/qxl.c
index 231d733250..afa157d327 100644
--- a/hw/display/qxl.c
+++ b/hw/display/qxl.c
@@ -1424,11 +1424,13 @@ static void qxl_reset_surfaces(PCIQXLDevice *d)
/* can be also called from spice server thread context */
static bool qxl_get_check_slot_offset(PCIQXLDevice *qxl, QXLPHYSICAL pqxl,
- uint32_t *s, uint64_t *o)
+ uint32_t *s, uint64_t *o,
+ size_t size_requested)
{
uint64_t phys = le64_to_cpu(pqxl);
uint32_t slot = (phys >> (64 - 8)) & 0xff;
uint64_t offset = phys & 0xffffffffffff;
+ uint64_t size_available;
if (slot >= NUM_MEMSLOTS) {
qxl_set_guest_bug(qxl, "slot too large %d >= %d", slot,
@@ -1453,6 +1455,18 @@ static bool qxl_get_check_slot_offset(PCIQXLDevice *qxl,
QXLPHYSICAL pqxl,
return false;
}
+ size_available = memory_region_size(qxl->guest_slots[slot].mr);
+ assert(qxl->guest_slots[slot].offset + offset < size_available);
Can this assertion be triggered by the guest (via an invalid pqxl
value)? I think the answer is no, but I don't know the the qxl code
well enough to be sure.
'qxl->guest_slots[slot].offset' is initialized in qxl_add_memslot()
(host); 'size_available' also comes from the host, but 'offset'
comes from the guest via 'QXLPHYSICAL pqxl' IIUC.
I added this check to avoid overflow, but it can be changed to return
an error.
Thanks,
Phil.
