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SubjectRe: [PATCH 06/11] compat_ioctl: remove /dev/random commands
On Tue, 11 Sep 2018 22:26:54 +0200
Arnd Bergmann <arnd@arndb.de> wrote:

> On Sun, Sep 9, 2018 at 6:12 AM Al Viro <viro@zeniv.linux.org.uk> wrote:
> >
> > On Sat, Sep 08, 2018 at 04:28:12PM +0200, Arnd Bergmann wrote:
> > > These are all handled by the random driver, so instead of listing
> > > each ioctl, we can just use the same function to deal with both
> > > native and compat commands.
> >
> > Umm... I don't think it's right -
> >
> > > .unlocked_ioctl = random_ioctl,
> > > + .compat_ioctl = random_ioctl,
> >
> >
> > ->compat_ioctl() gets called in
> > error = f.file->f_op->compat_ioctl(f.file, cmd, arg);
> > so you do *NOT* get compat_ptr() for those - they have to do it on their
> > own. It's not hard to provide a proper compat_ioctl() instance for that
> > one, but this is not it. What you need in drivers/char/random.c part of
> > that one is something like
>
> Looping in some s390 folks.
>
> As you suggested in another reply, I had a look at what other drivers
> do the same thing and have only pointer arguments. I created a
> patch to move them all over to using a new helper function that
> adds the compat_ptr(), and arrived at
>
> drivers/android/binder.c | 2 +-
> drivers/crypto/qat/qat_common/adf_ctl_drv.c | 2 +-
> drivers/dma-buf/dma-buf.c | 4 +---
> drivers/dma-buf/sw_sync.c | 2 +-
> drivers/dma-buf/sync_file.c | 2 +-
> drivers/gpu/drm/amd/amdkfd/kfd_chardev.c | 2 +-
> drivers/hid/hidraw.c | 4 +---
> drivers/iio/industrialio-core.c | 2 +-
> drivers/infiniband/core/uverbs_main.c | 4 ++--
> drivers/media/rc/lirc_dev.c | 4 +---
> drivers/mfd/cros_ec_dev.c | 4 +---
> drivers/misc/vmw_vmci/vmci_host.c | 2 +-
> drivers/nvdimm/bus.c | 4 ++--
> drivers/nvme/host/core.c | 6 +++---
> drivers/pci/switch/switchtec.c | 2 +-
> drivers/platform/x86/wmi.c | 2 +-
> drivers/rpmsg/rpmsg_char.c | 4 ++--
> drivers/s390/char/sclp_ctl.c | 8 ++------
> drivers/s390/char/vmcp.c | 2 ++----
> drivers/s390/cio/chsc_sch.c | 8 ++------
> drivers/sbus/char/display7seg.c | 2 +-
> drivers/sbus/char/envctrl.c | 4 +---
> drivers/scsi/3w-xxxx.c | 4 +---
> drivers/scsi/cxlflash/main.c | 2 +-
> drivers/scsi/esas2r/esas2r_main.c | 2 +-
> drivers/scsi/pmcraid.c | 4 +---
> drivers/staging/android/ion/ion.c | 4 +---
> drivers/staging/vme/devices/vme_user.c | 2 +-
> drivers/tee/tee_core.c | 2 +-
> drivers/usb/class/cdc-wdm.c | 2 +-
> drivers/usb/class/usbtmc.c | 4 +---
> drivers/video/fbdev/ps3fb.c | 2 +-
> drivers/video/fbdev/sis/sis_main.c | 4 +---
> drivers/virt/fsl_hypervisor.c | 2 +-
> fs/btrfs/super.c | 2 +-
> fs/ceph/dir.c | 2 +-
> fs/ceph/file.c | 2 +-
> fs/fuse/dev.c | 2 +-
> fs/notify/fanotify/fanotify_user.c | 2 +-
> fs/userfaultfd.c | 2 +-
> net/rfkill/core.c | 2 +-
> 41 files changed, 48 insertions(+), 76 deletions(-)
>
> Out of those, there are only a few that may get used on s390,
> in particular at most infiniband/uverbs, nvme, nvdimm,
> btrfs, ceph, fuse, fanotify and userfaultfd.
> [Note: there are three s390 drivers in the list, which use
> a different method: they check in_compat_syscall() from
> a shared handler to decide whether to do compat_ptr().

Using in_compat_syscall() seems to be a good solution, no?

> According to my memory from when I last worked on this,
> the compat_ptr() is mainly a safeguard for legacy binaries
> that got created with ancient C compilers (or compilers for
> something other than C) and might leave the high bit set
> in a pointer, but modern C compilers (gcc-3+) won't ever
> do that.

And compat_ptr clears the upper 32-bit of the register. If
the register is loaded to e.g. "lr" or "l" there will be
junk in the 4 upper bytes.

> You are probably right about /dev/random, which could be
> used in lots of weird code, but I wonder to what degree we
> need to worry about it for the rest.

--
blue skies,
Martin.

"Reality continues to ruin my life." - Calvin.

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