On Thu, Jul 16, 2026 at 10:55:42AM +0200, David Hildenbrand (Arm) wrote: > On 7/15/26 18:41, Hari Mishal wrote: > > The device_block_size read from the virtio-mem config space is used as a > > divisor and also in ALIGN_DOWN() further down the code path in the > > driver without further validation. A zero value leads to a division by > > zero, and a non-power-of-two value corrupts the ALIGN_DOWN() bitmask > > arithmetic leading to a misreporting of guest-usable ram, post crash. > > > > Reject both at init time instead of trusting the device. > > > > Signed-off-by: Hari Mishal <[email protected]> > > --- > > v2: dropped the redundant explicit zero check, since > > is_power_of_2(0) already returns false. > > > > drivers/virtio/virtio_mem.c | 6 ++++++ > > 1 file changed, 6 insertions(+) > > > > diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c > > index 11c441501582..0e04fec458af 100644 > > --- a/drivers/virtio/virtio_mem.c > > +++ b/drivers/virtio/virtio_mem.c > > @@ -2847,6 +2847,12 @@ static int virtio_mem_init(struct virtio_mem *vm) > > &vm->plugged_size); > > virtio_cread_le(vm->vdev, struct virtio_mem_config, block_size, > > &vm->device_block_size); > > + if (!is_power_of_2(vm->device_block_size)) { > > + dev_err(&vm->vdev->dev, > > + "invalid device block size: 0x%llx\n", > > + (unsigned long long)vm->device_block_size); > > + return -EINVAL; > > + } > > The spec states "The device MUST set block_size to a power of two." > > I'm missing the point here.
So what happens if we have a non-spec-compliant device? Shouldn't we be attempting to verify this before doing something with the data? Or do we just always trust virtio mem devices explicitly? thanks, greg k-h
