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From: Arnd Bergmann <arnd@arndb.de>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: Linux FS-devel Mailing List <linux-fsdevel@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 01/17] compat_ioctl: add generic_compat_ioctl_ptrarg()
Date: Thu, 13 Sep 2018 12:29:02 +0200	[thread overview]
Message-ID: <CAK8P3a2PTaanqmJycLCJ5QgNFXONb7nVye1=TJST639wDBNpAQ@mail.gmail.com> (raw)
In-Reply-To: <20180913020757.GP19965@ZenIV.linux.org.uk>

On Thu, Sep 13, 2018 at 4:07 AM Al Viro <viro@zeniv.linux.org.uk> wrote:
>
> On Wed, Sep 12, 2018 at 05:01:02PM +0200, Arnd Bergmann wrote:
> > Many drivers have ioctl() handlers that are completely compatible
> > between 32-bit and 64-bit architectures, except for the argument
> > that is passed down from user space and may have to be passed
> > through compat_ptr() in order to become a valid 64-bit pointer.
> >
> > Using ".compat_ptr=generic_compat_ioctl_ptrarg" in file operations
> > should let us simplify a lot of those drivers to avoid #ifdef
> > checks, and convert additional drivers that don't have proper
> > compat handling yet.
>
> Just keep in mind that this should *only* be used when all
> ioctls implemented in a given instance do take pointers.
> Because otherwise you are asking for trouble - e.g. if one of
> them takes an u32 used as a bitmap, this will run into trouble
> as soon as somebody uses bit 31.  With no visible warnings.
>
> IOW, it shouldn't be used blindly and it should come with big
> fat warning.

I was hoping that the _ptrarg suffix gives enough warning here,
but maybe not. I was careful to only use it in cases that I
checked are safe, either using only pointer arguments, or
no arguments.

What we might do for further clarification (besides adding a
comment next to the declaration), would be to add a
complementary generic_compat_ioctl_intarg() that skips
the compat_ptr(). There are only a handful of drivers that
would use this though.

       Arnd

  reply	other threads:[~2018-09-13 15:38 UTC|newest]

Thread overview: 48+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-09-12 15:01 Arnd Bergmann
2018-09-12 15:01 ` [PATCH v2 02/17] compat_ioctl: move drivers to generic_compat_ioctl_ptrarg Arnd Bergmann
2018-09-12 15:33   ` Jason Gunthorpe
2018-09-12 16:20     ` Arnd Bergmann
2018-09-12 18:13   ` Greg Kroah-Hartman
2018-09-16 19:07   ` Jarkko Sakkinen
2018-09-12 15:01 ` [PATCH v2 03/17] compat_ioctl: use correct compat_ptr() translation in drivers Arnd Bergmann
2018-09-12 18:13   ` Greg Kroah-Hartman
2018-09-13  0:48   ` Andrew Donnellan
2018-09-13 11:03   ` Felipe Balbi
2018-09-12 15:01 ` [PATCH v2 04/17] ceph: fix compat_ioctl for ceph_dir_operations Arnd Bergmann
2018-09-12 16:12   ` David Laight
2018-09-12 16:25     ` Arnd Bergmann
2018-09-13  0:48   ` Yan, Zheng
2018-09-12 15:08 ` [PATCH v2 05/17] compat_ioctl: move more drivers to generic_compat_ioctl_ptrarg Arnd Bergmann
2018-09-12 15:08   ` [PATCH v2 06/17] compat_ioctl: move rtc handling into rtc-dev.c Arnd Bergmann
2018-09-12 20:00     ` Alexandre Belloni
2018-09-12 15:08   ` [PATCH v2 07/17] compat_ioctl: move tape handling into drivers Arnd Bergmann
2018-09-12 15:08   ` [PATCH v2 08/17] compat_ioctl: remove keyboard ioctl translation Arnd Bergmann
2018-09-12 15:08   ` [PATCH v2 09/17] compat_ioctl: remove HIDIO translation Arnd Bergmann
2018-09-12 15:56   ` [PATCH v2 05/17] compat_ioctl: move more drivers to generic_compat_ioctl_ptrarg Jason Gunthorpe
2018-09-12 15:58   ` Daniel Vetter
2018-09-12 16:01   ` Mauro Carvalho Chehab
2018-09-12 18:13   ` Greg Kroah-Hartman
2018-09-14 14:23   ` David Sterba
2018-09-14 20:35   ` Darren Hart
2018-09-14 20:57     ` Al Viro
2018-09-18 17:51       ` Darren Hart
2018-09-18 17:59         ` Jason Gunthorpe
2018-09-24 20:18           ` Arnd Bergmann
2018-09-24 20:35             ` Jason Gunthorpe
2018-09-24 21:17               ` Arnd Bergmann
2018-09-17  9:33   ` Jonathan Cameron
2018-10-06  7:05   ` Bjorn Andersson
2018-09-12 15:13 ` [PATCH v2 10/17] compat_ioctl: remove translation for sound ioctls Arnd Bergmann
2018-09-12 15:13   ` [PATCH v2 11/17] compat_ioctl: remove isdn ioctl translation Arnd Bergmann
2018-09-12 15:13   ` [PATCH v2 12/17] compat_ioctl: remove IGNORE_IOCTL() Arnd Bergmann
2018-09-12 15:13   ` [PATCH v2 13/17] compat_ioctl: remove /dev/random commands Arnd Bergmann
2018-09-12 18:13     ` Greg Kroah-Hartman
2018-09-12 15:13   ` [PATCH v2 14/17] compat_ioctl: remove joystick ioctl translation Arnd Bergmann
2018-09-12 15:13   ` [PATCH v2 15/17] compat_ioctl: remove PCI " Arnd Bergmann
2018-09-12 15:13   ` [PATCH v2 16/17] compat_ioctl: remove /dev/raw " Arnd Bergmann
2018-09-12 15:13   ` [PATCH v2 17/17] compat_ioctl: remove last RAID handling code Arnd Bergmann
2018-09-13 13:37   ` [PATCH v2 10/17] compat_ioctl: remove translation for sound ioctls Takashi Iwai
2018-09-13  2:07 ` [PATCH v2 01/17] compat_ioctl: add generic_compat_ioctl_ptrarg() Al Viro
2018-09-13 10:29   ` Arnd Bergmann [this message]
2018-10-28 17:07     ` Al Viro
2018-10-29  9:50       ` Arnd Bergmann

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