Messages in this thread | | | Date | Fri, 13 May 2016 16:54:01 -0400 | From | "ira.weiny" <> | Subject | 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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