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Date:   Thu, 25 Apr 2019 17:32:05 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Mauro Carvalho Chehab <mchehab+samsung@...nel.org>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
        y2038 Mailman List <y2038@...ts.linaro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Jason Gunthorpe <jgg@...lanox.com>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        David Sterba <dsterba@...e.com>,
        Darren Hart <dvhart@...radead.org>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        driverdevel <devel@...verdev.osuosl.org>, qat-linux@...el.com,
        "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" 
        <linux-crypto@...r.kernel.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        linaro-mm-sig@...ts.linaro.org, amd-gfx@...ts.freedesktop.org,
        "open list:HID CORE LAYER" <linux-input@...r.kernel.org>,
        linux-iio@...r.kernel.org, linux-rdma <linux-rdma@...r.kernel.org>,
        linux-nvdimm@...ts.01.org, linux-nvme@...ts.infradead.org,
        linux-pci <linux-pci@...r.kernel.org>,
        Platform Driver <platform-driver-x86@...r.kernel.org>,
        linux-remoteproc@...r.kernel.org,
        sparclinux <sparclinux@...r.kernel.org>,
        linux-scsi <linux-scsi@...r.kernel.org>,
        USB list <linux-usb@...r.kernel.org>,
        linux-btrfs <linux-btrfs@...r.kernel.org>,
        ceph-devel <ceph-devel@...r.kernel.org>,
        linux-wireless <linux-wireless@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>, Sean Young <sean@...s.org>
Subject: Re: [PATCH v3 12/26] compat_ioctl: move more drivers to compat_ptr_ioctl

On Thu, Apr 25, 2019 at 5:22 PM Mauro Carvalho Chehab
<mchehab+samsung@...nel.org> wrote:
> Em Tue, 16 Apr 2019 22:25:33 +0200 Arnd Bergmann <arnd@...db.de> escreveu:
>
> If I understand your patch description well, using compat_ptr_ioctl
> only works if the driver is not for s390, right?

No, the purpose of compat_ptr_ioctl() is to make sure it works
everywhere including s390.

Even on s390 it tends to work most of the time, but for correctness
the upper bit of a 32-bit pointer needs to be cleared, as
compat_ptr_ioctl does, in case some application passes a pointer
with that bit set. [IIRC, in the instruction pointer, the high bit is set, in
data references it is ignored but usually cleared, but it may be left
on for IP-relative address generation]

       Arnd

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