netdev - Re: [v2] vhost: add vsock compat ioctl

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Message-ID: <CAPz6YkV5FaQhO_2xbahagZw4mGFCcE8EXzmLw-dNkN4rmdKuVA@mail.gmail.com>
Date:   Thu, 22 Mar 2018 13:38:36 -0700
From:   Sonny Rao <sonnyrao@...omium.org>
To:     Stefan Hajnoczi <stefanha@...il.com>
Cc:     David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [v2] vhost: add vsock compat ioctl

On Thu, Mar 22, 2018 at 2:25 AM, Stefan Hajnoczi <stefanha@...il.com> wrote:
> On Fri, Mar 16, 2018 at 7:30 PM, David Miller <davem@...emloft.net> wrote:
>> Although the top level ioctls are probably size and layout compatible,
>> I do not think that the deeper ioctls can be called by compat binaries
>> without some translations in order for them to work.
>
> I audited the vhost ioctl code when reviewing this patch and was
> unable to find anything that would break for a 32-bit userspace
> process.
>
> drivers/vhost/net.c does the same thing already, which doesn't prove
> it's correct but makes me more confident I didn't miss something while
> auditing the vhost ioctl code.
>
> Did you have a specific ioctl in mind?

I think he means that we need to use the compat_ptr macro on any other
pointers we get from userspace in those other ioctls.  For most
architectures this macro doesn't seem to do much but it does on some
-- I think s390 modifies the pointer.

>
> Stefan