On 14/11/19 09:20, Christian Borntraeger wrote: > > > 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 :-) A comment in the code would probably be better than the commit message, to not forget stuff like this. (Hint! :)) Paolo
