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Re: [PATCH v2 3/5] IB/hfi1: Add ioctl() interface for user commands

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On Thu, May 12, 2016 at 01:40:06PM -0600, Jason Gunthorpe wrote:
> On Thu, May 12, 2016 at 03:27:27PM -0400, Dennis Dalessandro wrote:
> 
> > >>+static inline int check_ioctl_access(unsigned int cmd, unsigned long arg)
> > >>+{
> > >>+	int read_cmd, write_cmd, read_ok, write_ok;
> > >>+
> > >>+	read_cmd = _IOC_DIR(cmd) & _IOC_READ;
> > >>+	write_cmd = _IOC_DIR(cmd) & _IOC_WRITE;
> > >>+	write_ok = access_ok(VERIFY_WRITE, (void __user *)arg, _IOC_SIZE(cmd));
> > >>+	read_ok = access_ok(VERIFY_READ, (void __user *)arg, _IOC_SIZE(cmd));
> > >>+
> > >>+	if ((read_cmd && !write_ok) || (write_cmd && !read_ok))
> > >>+		return -EFAULT;
> > >
> > >This seems kind of goofy, didn't Ira say this is performance senstive?
> 
> Well, calling access_ok twice when only once is typically needed is
> certainly not performant. Typically this check is done at every access
> via get_user/put_user/copy_to/from_user - why is it being hoisted like
> this?
>
> 
> > >Driver shouldn't be open coding __get_user like that, IMHO.
> > 
> > Can you explain what you mean here? We should not use __get_user()?
> 
> Generally speaking, yes. Use get_user() that includes the correct
> access_ok. Unless there is a good reason to avoid it, the standard API
> should be used.

I know this code was refactored while we were still submitting patches to Greg
KH back in Nov/Dec.  Part of this was cleaning up branch on error rather than
success.  Hence the check for access at the top of the function and early
return.

At that time I _thought_ there were multiple __get_users in some of the
operations so a single common access_ok would speed those up.  However, I don't
see that happening any longer, so either I don't remember correctly, or we have
made this cleaner.

As it stands now I think you are correct we could use get_user and
copy_to/from_user.

Ira

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[PATCH v2 0/5] IB/hfi1: Remove write() and use ioctl() for user  access Dennis Dalessandro <dennis.dalessandro@intel.com> - 2016-05-12 19:20 +0200
  [PATCH v2 3/5] IB/hfi1: Add ioctl() interface for user commands Dennis Dalessandro <dennis.dalessandro@intel.com> - 2016-05-12 19:20 +0200
    Re: [PATCH v2 3/5] IB/hfi1: Add ioctl() interface for user commands Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2016-05-12 19:50 +0200
      RE: [PATCH v2 3/5] IB/hfi1: Add ioctl() interface for user commands "Hefty, Sean" <sean.hefty@intel.com> - 2016-05-12 20:20 +0200
      Re: [PATCH v2 3/5] IB/hfi1: Add ioctl() interface for user commands Dennis Dalessandro <dennis.dalessandro@intel.com> - 2016-05-12 21:30 +0200
        Re: [PATCH v2 3/5] IB/hfi1: Add ioctl() interface for user commands Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2016-05-12 21:50 +0200
          Re: [PATCH v2 3/5] IB/hfi1: Add ioctl() interface for user commands Doug Ledford <dledford@redhat.com> - 2016-05-12 21:50 +0200
            Re: [PATCH v2 3/5] IB/hfi1: Add ioctl() interface for user commands Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2016-05-12 23:30 +0200
              Re: [PATCH v2 3/5] IB/hfi1: Add ioctl() interface for user commands Dennis Dalessandro <dennis.dalessandro@intel.com> - 2016-05-13 16:40 +0200
          Re: [PATCH v2 3/5] IB/hfi1: Add ioctl() interface for user commands "ira.weiny" <ira.weiny@intel.com> - 2016-05-13 23:00 +0200
  [PATCH v2 1/5] IB/hfi1: Export drivers user sw version via sysfs Dennis Dalessandro <dennis.dalessandro@intel.com> - 2016-05-12 19:20 +0200
  [PATCH v2 2/5] IB/hfi1: Remove unused user command Dennis Dalessandro <dennis.dalessandro@intel.com> - 2016-05-12 19:20 +0200
  [PATCH v2 4/5] IB/hfi1: Remove write(), use ioctl() for user cmds Dennis Dalessandro <dennis.dalessandro@intel.com> - 2016-05-12 19:20 +0200
  [PATCH v2 5/5] IB/hfi1: Add trace message in user IOCTL handling Dennis Dalessandro <dennis.dalessandro@intel.com> - 2016-05-12 19:20 +0200
  Re: [PATCH v2 0/5] IB/hfi1: Remove write() and use ioctl() for user  access Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2016-05-12 19:40 +0200
    Re: [PATCH v2 0/5] IB/hfi1: Remove write() and use ioctl() for user access Dennis Dalessandro <dennis.dalessandro@intel.com> - 2016-05-12 21:10 +0200
      Re: [PATCH v2 0/5] IB/hfi1: Remove write() and use ioctl() for user  access Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2016-05-12 21:30 +0200
        Re: [PATCH v2 0/5] IB/hfi1: Remove write() and use ioctl() for user access Dennis Dalessandro <dennis.dalessandro@intel.com> - 2016-05-12 22:00 +0200
          Re: [PATCH v2 0/5] IB/hfi1: Remove write() and use ioctl() for user  access Doug Ledford <dledford@redhat.com> - 2016-05-12 22:40 +0200
          Re: [PATCH v2 0/5] IB/hfi1: Remove write() and use ioctl() for user  access Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2016-05-12 23:30 +0200

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