Re: [PATCH 3/5] misc: mlx5ctl: Add info ioctl

[Leon Romanovsky]

On Wed, Oct 18, 2023 at 11:02:00AM +0200, Arnd Bergmann wrote:
> On Wed, Oct 18, 2023, at 10:19, Saeed Mahameed wrote:
> 
> > Implement INFO ioctl to return the allocated UID and the capability flags
> > and some other useful device information such as the underlying ConnectX
> > device.
> 
> I'm commenting on the ABI here, ignoring everything for the moment.
> 
> >  static const struct file_operations mlx5ctl_fops = {
> >  	.owner = THIS_MODULE,
> >  	.open = mlx5ctl_open,
> >  	.release = mlx5ctl_release,
> > +	.unlocked_ioctl = mlx5ctl_ioctl,
> >  };
> 
> There should be a .compat_ioctl entry as well, to allow 32-bit
> tasks to use the same interface.

Even for new code as well?

Both kernel and userspace code is new, not released yet.

>  
> >  static int mlx5ctl_probe(struct auxiliary_device *adev,
> > diff --git a/include/uapi/misc/mlx5ctl.h b/include/uapi/misc/mlx5ctl.h
> > new file mode 100644
> > index 000000000000..81d89cd285fc
> > --- /dev/null
> > +++ b/include/uapi/misc/mlx5ctl.h
> > @@ -0,0 +1,24 @@
> > +/* SPDX-License-Identifier: GPL-2.0 OR Linux-OpenIB WITH Linux-syscall-note */
> > +/* Copyright (c) 2023, NVIDIA CORPORATION & AFFILIATES. All rights reserved. */
> > +
> > +#ifndef __MLX5CTL_IOCTL_H__
> > +#define __MLX5CTL_IOCTL_H__
> > +
> > +struct mlx5ctl_info {
> > +	__aligned_u64 flags;
> > +	__u32 size;
> > +	__u8 devname[64]; /* underlaying ConnectX device */
> > +	__u16 uctx_uid; /* current process allocated UCTX UID */
> 
> I don't know what a UCTX UID is, but if this is related to
> uid_t, it has to be 32 bit wide.

UCTX UID is mlx5 hardware index, it is not uid_t.

> 
> > +	__u16 reserved1;
> > +	__u32 uctx_cap; /* current process effective UCTX cap */
> > +	__u32 dev_uctx_cap; /* device's UCTX capabilities */
> > +	__u32 ucap; /* process user capability */
> > +	__u32 reserved2[4];
> > +};
> 
> If I'm counting right, this structure has a size of
> 108 bytes but an alignment of 8 bytes, so you end up with
> a 4-byte hole at the end, which introduces a risk of
> leaking kernel data. Maybe give it an extra reserved word?

I think that he needs to delete __u32 reserved2[4]; completely.

Thanks

> 
>      Arnd