linux-kernel - RE: [PATCH v3 3/8] platform/x86: dell-wmi-smbios: Use Dell WMI descriptor check

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Date:   Sat, 30 Sep 2017 19:48:39 +0000
From:   <Mario.Limonciello@...l.com>
To:     <dvhart@...radead.org>
CC:     <andy.shevchenko@...il.com>, <linux-kernel@...r.kernel.org>,
        <platform-driver-x86@...r.kernel.org>, <luto@...nel.org>,
        <quasisec@...gle.com>, <pali.rohar@...il.com>
Subject: RE: [PATCH v3 3/8] platform/x86: dell-wmi-smbios: Use Dell WMI
 descriptor check

> -----Original Message-----
> From: Darren Hart [mailto:dvhart@...radead.org]
> Sent: Friday, September 29, 2017 8:29 PM
> To: Limonciello, Mario <Mario_Limonciello@...l.com>
> Cc: Andy Shevchenko <andy.shevchenko@...il.com>; LKML <linux-
> kernel@...r.kernel.org>; platform-driver-x86@...r.kernel.org; Andy Lutomirski
> <luto@...nel.org>; quasisec@...gle.com; pali.rohar@...il.com
> Subject: Re: [PATCH v3 3/8] platform/x86: dell-wmi-smbios: Use Dell WMI
> descriptor check
> 
> On Wed, Sep 27, 2017 at 11:02:15PM -0500, Mario Limonciello wrote:
> > The Dell WMI descriptor check is used as an indication that WMI
> > calls are safe to run both when used with the notification
> > ASL/GUID pair as well as the SMBIOS calling ASL/GUID pair.
> >
> > As some code in dell-wmi-smbios is already a prerequisite for
> > dell-wmi, move the code for performing the descriptor check into
> > dell-wmi-smbios and let both drivers use it from there.
> >
> > Signed-off-by: Mario Limonciello <mario.limonciello@...l.com>
> > ---
> ...
> > diff --git a/drivers/platform/x86/dell-smbios.c b/drivers/platform/x86/dell-
> smbios.c
> ...
> >
> > +/*
> > + * Descriptor buffer is 128 byte long and contains:
> ...
> > +	if (obj->buffer.length != 128) {
> > +		dev_err(&wdev->dev,
> > +			"Dell descriptor buffer has invalid length (%d)\n",
> > +			obj->buffer.length);
> 
> This seems odd. We call it an error (not a warning) if != 128, but we only abort
> and return an error if it's < 16.
> 
> If it's an error, we should return an error code, if anything above 16 is
> acceptable but 128 is preferred, the above should be a warning at best. (this
> scenario seems unlikely).

Hopefully the original author can speak up to the intentions here.  I would feel
that it should have errored out if it wasn't expected length too.

> 
> > +		if (obj->buffer.length < 16) {
> > +			ret = -EINVAL;
> > +			goto out;
> > +		}
> > +	}
> > +	desc_buffer = (u32 *)obj->buffer.pointer;
> > +
> > +	if (desc_buffer[0] != 0x4C4C4544 && desc_buffer[1] != 0x494D5720)
> 
> This seems like it should be an || ?
> 
> (I see this is fixed in a later patch)
> 
> I would have suggested fixing it, then moving it - just from a pure ease of
> review perspective. Perhaps not in the comment above that this is a verbatim
> move, some fixes are coming in subsequent patches. This is worth noting for a
> future develop who may be choosing what to backport.
> 

I'll re-order things so that the fixes come before the move.

> >  static int dell_smbios_wmi_probe(struct wmi_device *wdev)
> >  {
> > +	int ret;
> > +	u32 interface_version;
> 
> Declarations in order of decreasing line length please.
> 
> > @@ -236,6 +316,7 @@ static int dell_smbios_wmi_probe(struct wmi_device
> *wdev)
> >  	if (!buffer)
> >  		return -ENOMEM;
> >  	bufferlen = sizeof(struct wmi_calling_interface_buffer);
> > +
> 
> Stray whitespace, should have been in the previous patch I guess?
> 
> 
> --
> Darren Hart
> VMware Open Source Technology Center