linux-kernel - Re: [PATCH 1/1] dmi_scan: uuid: fix endianess for smbios >= 0x206

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Message-ID: <20160106140133.7376ec04@endymion.delvare>
Date:	Wed, 6 Jan 2016 14:01:33 +0100
From:	Jean Delvare <jdelvare@...e.de>
To:	Matt Fleming <matt@...eblueprint.co.uk>
Cc:	Andrea Arcangeli <aarcange@...hat.com>,
	Ivan Khoronzhuk <ivan.khoronzhuk@...aro.org>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Federico Simoncelli <fsimonce@...hat.com>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/1] dmi_scan: uuid: fix endianess for smbios >= 0x206

Hi Matt, Andrea,

On Tue, 22 Dec 2015 15:17:51 +0000, Matt Fleming wrote:
> (Cc'ing Jean since he's the maintainer)
> 
> On Tue, 22 Dec, at 02:53:10PM, Andrea Arcangeli wrote:
> > The dmi_ver wasn't updated correctly before the dmi_decode method run
> > to save the uuid.
> > 
> > That resulted in "dmidecode -s system-uuid" and
> > /sys/class/dmi/id/product_uuid disagreeing. The latter was buggy and
> > this fixes it.
> > 
> > Reported-by: Federico Simoncelli <fsimonce@...hat.com>
> > Signed-off-by: Andrea Arcangeli <aarcange@...hat.com>
> > ---
> >  drivers/firmware/dmi_scan.c | 6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/firmware/dmi_scan.c b/drivers/firmware/dmi_scan.c
> > index ac1ce4a..0e08e66 100644
> > --- a/drivers/firmware/dmi_scan.c
> > +++ b/drivers/firmware/dmi_scan.c
> > @@ -521,6 +521,7 @@ static int __init dmi_present(const u8 *buf)
> >  			dmi_ver = smbios_ver;
> >  		else
> >  			dmi_ver = (buf[14] & 0xF0) << 4 | (buf[14] & 0x0F);
> > +		dmi_ver <<= 8;
> >  		dmi_num = get_unaligned_le16(buf + 12);
> >  		dmi_len = get_unaligned_le16(buf + 6);
> >  		dmi_base = get_unaligned_le32(buf + 8);
> > @@ -528,15 +529,14 @@ static int __init dmi_present(const u8 *buf)
> >  		if (dmi_walk_early(dmi_decode) == 0) {
> >  			if (smbios_ver) {
> >  				pr_info("SMBIOS %d.%d present.\n",
> > -				       dmi_ver >> 8, dmi_ver & 0xFF);
> > +					dmi_ver >> 16, (dmi_ver >> 8) & 0xFF);
> >  			} else {
> >  				smbios_entry_point_size = 15;
> >  				memcpy(smbios_entry_point, buf,
> >  				       smbios_entry_point_size);
> >  				pr_info("Legacy DMI %d.%d present.\n",
> > -				       dmi_ver >> 8, dmi_ver & 0xFF);
> > +					dmi_ver >> 16, (dmi_ver >> 8) & 0xFF);
> >  			}
> > -			dmi_ver <<= 8;
> >  			dmi_format_ids(dmi_ids_string, sizeof(dmi_ids_string));
> >  			printk(KERN_DEBUG "DMI: %s\n", dmi_ids_string);
> >  			return 0;

Baaah. This was supposed to be fixed by my commit
5c1ac56b51b9d222ab202dec1ac2f4215346129d ("firmware: dmi_scan: Fix
ordering of product_uuid") but clearly I missed half of the required
changes. Should have tested...

The irony is that I clearly remember when reviewing Ivan's patches that
I did not like this part of the code. Quoting myself:

"I understand this was the easiest way to implement the change, but I'm
not really comfortable with dmi_ver having different formats for
different parts of the code. This is rather error prone for future
changes, even if the code is currently correct."

Even though I was wrong when claiming that the code was "currently
correct", I should have listened to my gut feeling back then and asked
for a different implementation.

Anyway... Thanks Andrea, applied with the missing "Fixes:" markers
added. I'll send to Linus soon.

-- 
Jean Delvare
SUSE L3 Support
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