linux-kernel - Re: __user with scalar data types

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Message-ID: <CAKMK7uFdH4VBftjyVCbXqcu76qMTSvkVFRDB3tJtX3N+SNm72w@mail.gmail.com>
Date:   Tue, 20 Jun 2017 09:12:23 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Al Viro <viro@...iv.linux.org.uk>,
        "Clark, Rob" <robdclark@...il.com>,
        Gerd Hoffmann <kraxel@...hat.com>
Cc:     linux-sparse@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>
Subject: Re: __user with scalar data types

On Mon, Jun 19, 2017 at 6:34 PM, Al Viro <viro@...iv.linux.org.uk> wrote:
> On Mon, Jun 19, 2017 at 10:15:09AM -0600, Jordan Crouse wrote:
>
>> Which raised a bikeshed debate over whether it is appropriate to mark a scalar
>> type as __user.  My opinion is that it is appropriate because __user should mark
>> user memory regardless of the container.
>
> What the hell?  __user is a qualifier like const, volatile, etc.  It's a property
> of *pointer* *type*.  Not some nebulous "marks userland memory" thing.
>
>> I'm looking for opinions or semi-authoritative edicts to determine if we should
>> either start changing our uapi headers or go off and try to figure out how to
>> make sparse understand this particular usage.
>
> Stop cargo-culting, please.

Yep that's cargo-culted, but from a quick grep only msm and qxl
headers do this (the other __user annotations in uapi/drm are for
pointers, where it's correct). Adding those maintainers.

Also, if you use u64_to_user_ptr helper macro sparse should have
caught this (if not we'd need to improve the macro).
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch