On Mon, 28 Nov 2022 at 10:25, Philippe Mathieu-Daudé <phi...@linaro.org> wrote: > > 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.
Yes, please. Aside from concerns about -DNDEBUG, which builds without assertions, there is also a DoS issue with nested virt where an L2 guest shouldn't be able to abort the L1 guest's QEMU by triggering an assertion in a pass through device. Guest input validation should use explicit error checking code instead of assert(3). Thanks, Stefan