linux-kernel - Re: [PATCH] Ability to read the MKTME status from userspace

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Date:   Fri, 19 Jun 2020 16:02:06 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Daniel Gutson <daniel@...ypsium.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Arnd Bergmann <arnd@...db.de>,
        Peter Zijlstra <peterz@...radead.org>,
        "David S. Miller" <davem@...emloft.net>,
        Rob Herring <robh@...nel.org>, Tony Luck <tony.luck@...el.com>,
        Rahul Tanwar <rahul.tanwar@...ux.intel.com>,
        Xiaoyao Li <xiaoyao.li@...el.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Ability to read the MKTME status from userspace

On Fri, Jun 19, 2020 at 10:51:32AM -0300, Daniel Gutson wrote:
> > > +enum mktme_status_type get_mktme_status(void)
> > > +{
> > > +     return mktme_status;
> > > +}
> > > +EXPORT_SYMBOL_GPL(get_mktme_status);
> >
> > prefix of the subsystem first please:
> >         mktme_get_status
> >
> 
> OK.
> 
> > Or, better yet, why not just export the variable directly?  Why is this
> > a function at all?
> 
> Because I want this to be read only.

read-only to who?

> > > +
> > > +/* Buffer to return: always 3 because of the following chars:
> > > + *     value \n \0
> > > + */
> > > +#define BUFFER_SIZE 3
> >
> > Why a define?
> 
> Do you suggest `static const int` instead?

Why do you need it at all?

> > > +
> > > +     sprintf(tmp, "%d\n", (int)get_mktme_status() & 1);
> > > +     return simple_read_from_buffer(buf, count, ppos, tmp, sizeof(tmp));
> > > +}
> > > +
> > > +static const struct file_operations mktme_status_ops = {
> > > +     .read = mktme_status_read,
> > > +};
> > > +
> > > +static int __init mod_init(void)
> > > +{
> > > +     mktme_dir = securityfs_create_dir("mktme", NULL);
> > > +     if (IS_ERR(mktme_dir)) {
> > > +             pr_err("Couldn't create mktme sysfs dir\n");
> > > +             return -1;
> >
> > Don't make up random error numbers, use the EWHATEVER defines please.
> >
> 
> Could you please suggest one?

Why not return the error given to you?  Why throw that information away?

> > Also no Documentation/ABI/ update for your new userspace api that you
> > just created?
> >
> 
> should that be a comment in the .h?

No, you need a description in Documentation/ABI/ about any
sysfs/configfs/securityfs/whatever for new things you are creating.

thanks,

greg k-h