On Mon, Jul 16, 2012 at 08:16:12PM +0200, Dominic Eschweiler wrote: > Am Freitag, den 13.07.2012, 21:19 +0300 schrieb Michael S. Tsirkin: > > > > UIO has the same property, doesn't it? Multiple users can > > access device memory through sysfs. > > > Indeed, that's a similar problem. I haven't tried it (yet), but this > particular problem can maybe circumvented by using mmap with the > MAP_PRIVATE flag. Doing so is the responsibility of the driver > programmer (like Hans already said). Even if that mmap trick does not > work, it is pretty much sure that a BAR is already used by another > program, if a related kernel driver is loaded. In that case the kernel > has a chance to avoid such BAR race conditions by not giving the > possibility to map them to the userspace. Don't make it more complicated than it is. I see no general problem in mapping BARs in uio_pci_generic like in any other UIO PCI driver. > > Nevertheless, I'm pretty sure that the possibility via sysfs to access > BARs, which are already managed by a kernel driver, opens the door for > denial of service attacks. There are also a few other possible attack scenarios, depending on the hardware. That's a general problem of all userspace drivers (e.g. X graphics drivers). You have to make sure access rights are correct. Making a UIO device node available to all normal users is foolishly dangerous. > > On the other hand, I'm quite a newbie on this topic and maybe I don't > see the big picture here. Therefore it is up to you guys to make the > right decision (if needed). Try to hack up a patch to add generic BAR mapping to uio_pci_generic.c and post it for review. Thanks, Hans -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
