On 14.11.19 09:15, Marc Zyngier wrote: > On Wed, 13 Nov 2019 21:23:07 +0000 > Peter Maydell <peter.maydell@xxxxxxxxxx> wrote: > >> On Wed, 13 Nov 2019 at 18:44, Christian Borntraeger >> <borntraeger@xxxxxxxxxx> wrote: >>> On 13.11.19 17:05, Marc Zyngier wrote: >>>> On a system without KVM_COMPAT, we prevent IOCTLs from being issued >>>> by a compat task. Although this prevents most silly things from >>>> happening, it can still confuse a 32bit userspace that is able >>>> to open the kvm device (the qemu test suite seems to be pretty >>>> mad with this behaviour). >>>> >>>> Take a more radical approach and return a -ENODEV to the compat >>>> task. >> >>> Do we still need compat_ioctl if open never succeeds? >> >> I wondered about that, but presumably you could use >> fd-passing, or just inheriting open fds across exec(), >> to open the fd in a 64-bit process and then hand it off >> to a 32-bit process to call the ioctl with. (That's >> probably only something you'd do if you were >> deliberately playing silly games, of course, but >> preventing silly games is useful as it makes it >> easier to reason about kernel behaviour.) > > This was exactly my train of thoughts, which I should have made clear > in the commit log. Thanks Peter for reading my mind! ;-) Makes sense. Looks like this is already in kvm/master so we cannot improve the commit message easily any more. Hopefully we will not forget :-)
