[Qemu-devel] bug: incorrect uuid in seabios output

[Qemu-devel] bug: incorrect uuid in seabios output

[Cole Robinson]

Hi,

The UUID seabios reports in its boot output doesn't match what is passed via
qemu -uuid option. An example is reported here:

https://bugzilla.redhat.com/show_bug.cgi?id=1284259

This is due to:

commit caad057bb6ce86a9cb71520af395fd0bd04a659f
Author: Eduardo Habkost <ehabkost@redhat.com>
Date:   Wed Oct 29 11:26:08 2014 -0200

    smbios: Encode UUID according to SMBIOS specification

    Differently from older versions, SMBIOS version 2.6 is explicit about
    the encoding of UUID fields:

    > Although RFC 4122 recommends network byte order for all fields, the PC
    > industry (including the ACPI, UEFI, and Microsoft specifications) has
    > consistently used little-endian byte encoding for the first three fields:
    > time_low, time_mid, time_hi_and_version. The same encoding, also known as
    > wire format, should also be used for the SMBIOS representation of the UUID.
    >
    > The UUID {00112233-4455-6677-8899-AABBCCDDEEFF} would thus be represented
    > as 33 22 11 00 55 44 77 66 88 99 AA BB CC DD EE FF.

    The dmidecode tool implements this and decodes the above "wire format"
    when SMBIOS version >= 2.6. We moved from SMBIOS version 2.4 to 2.8 when
    we started building the SMBIOS entry point inside QEMU, on commit
    c97294ec1b9e36887e119589d456557d72ab37b5.


seabios doesn't seem to handle this special UUID format when reading from smbios.

Thanks,
Cole

Re: [Qemu-devel] [SeaBIOS] bug: incorrect uuid in seabios output

[Gerd Hoffmann]

On Di, 2015-11-24 at 11:55 -0500, Cole Robinson wrote:
> Hi,
> 
> The UUID seabios reports in its boot output doesn't match what is passed via
> qemu -uuid option. An example is reported here:
> 
> https://bugzilla.redhat.com/show_bug.cgi?id=1284259
> 
> This is due to:
> 
> commit caad057bb6ce86a9cb71520af395fd0bd04a659f
> Author: Eduardo Habkost <ehabkost@redhat.com>
> Date:   Wed Oct 29 11:26:08 2014 -0200
> 
>     smbios: Encode UUID according to SMBIOS specification
> 
>     Differently from older versions, SMBIOS version 2.6 is explicit about
>     the encoding of UUID fields:
> 
>     > Although RFC 4122 recommends network byte order for all fields, the PC
>     > industry (including the ACPI, UEFI, and Microsoft specifications) has
>     > consistently used little-endian byte encoding for the first three fields:
>     > time_low, time_mid, time_hi_and_version. The same encoding, also known as
>     > wire format, should also be used for the SMBIOS representation of the UUID.
>     >
>     > The UUID {00112233-4455-6677-8899-AABBCCDDEEFF} would thus be represented
>     > as 33 22 11 00 55 44 77 66 88 99 AA BB CC DD EE FF.
> 
>     The dmidecode tool implements this and decodes the above "wire format"
>     when SMBIOS version >= 2.6. We moved from SMBIOS version 2.4 to 2.8 when
>     we started building the SMBIOS entry point inside QEMU, on commit
>     c97294ec1b9e36887e119589d456557d72ab37b5.
> 
> 
> seabios doesn't seem to handle this special UUID format when reading from smbios.

Hmm.  Changing the ordering in display_uuid() is easy.  There seems to
be no easy way to figure which format to use though.  Checking the
version like dmidecode doesn't fly as there are qemu versions with old
format but version smbios 2.8 in the wild ...

cheers,
  Gerd

Re: [Qemu-devel] [SeaBIOS] bug: incorrect uuid in seabios output

[Laszlo Ersek]

On 11/26/15 08:43, Gerd Hoffmann wrote:
> On Di, 2015-11-24 at 11:55 -0500, Cole Robinson wrote:
>> Hi,
>>
>> The UUID seabios reports in its boot output doesn't match what is passed via
>> qemu -uuid option. An example is reported here:
>>
>> https://bugzilla.redhat.com/show_bug.cgi?id=1284259
>>
>> This is due to:
>>
>> commit caad057bb6ce86a9cb71520af395fd0bd04a659f
>> Author: Eduardo Habkost <ehabkost@redhat.com>
>> Date:   Wed Oct 29 11:26:08 2014 -0200
>>
>>     smbios: Encode UUID according to SMBIOS specification
>>
>>     Differently from older versions, SMBIOS version 2.6 is explicit about
>>     the encoding of UUID fields:
>>
>>     > Although RFC 4122 recommends network byte order for all fields, the PC
>>     > industry (including the ACPI, UEFI, and Microsoft specifications) has
>>     > consistently used little-endian byte encoding for the first three fields:
>>     > time_low, time_mid, time_hi_and_version. The same encoding, also known as
>>     > wire format, should also be used for the SMBIOS representation of the UUID.
>>     >
>>     > The UUID {00112233-4455-6677-8899-AABBCCDDEEFF} would thus be represented
>>     > as 33 22 11 00 55 44 77 66 88 99 AA BB CC DD EE FF.
>>
>>     The dmidecode tool implements this and decodes the above "wire format"
>>     when SMBIOS version >= 2.6. We moved from SMBIOS version 2.4 to 2.8 when
>>     we started building the SMBIOS entry point inside QEMU, on commit
>>     c97294ec1b9e36887e119589d456557d72ab37b5.
>>
>>
>> seabios doesn't seem to handle this special UUID format when reading from smbios.
> 
> Hmm.  Changing the ordering in display_uuid() is easy.  There seems to
> be no easy way to figure which format to use though.  Checking the
> version like dmidecode doesn't fly as there are qemu versions with old
> format but version smbios 2.8 in the wild ...

Plus, because this is guest visible, Eduardo's patch noted above only
changes the encoding for 2.2 and later QEMU machine types. If you run
your reproducer but flip the machine type to 2.1 or earlier, you should
see the UUID on the SeaBIOS screen change.

Thanks
Laszlo

Re: [Qemu-devel] [SeaBIOS] bug: incorrect uuid in seabios output

[Eduardo Habkost]

On Thu, Nov 26, 2015 at 07:40:10PM +0100, Laszlo Ersek wrote:
> On 11/26/15 08:43, Gerd Hoffmann wrote:
> > On Di, 2015-11-24 at 11:55 -0500, Cole Robinson wrote:
> >> Hi,
> >>
> >> The UUID seabios reports in its boot output doesn't match what is passed via
> >> qemu -uuid option. An example is reported here:
> >>
> >> https://bugzilla.redhat.com/show_bug.cgi?id=1284259
> >>
> >> This is due to:
> >>
> >> commit caad057bb6ce86a9cb71520af395fd0bd04a659f
> >> Author: Eduardo Habkost <ehabkost@redhat.com>
> >> Date:   Wed Oct 29 11:26:08 2014 -0200
> >>
> >>     smbios: Encode UUID according to SMBIOS specification
> >>
> >>     Differently from older versions, SMBIOS version 2.6 is explicit about
> >>     the encoding of UUID fields:
> >>
> >>     > Although RFC 4122 recommends network byte order for all fields, the PC
> >>     > industry (including the ACPI, UEFI, and Microsoft specifications) has
> >>     > consistently used little-endian byte encoding for the first three fields:
> >>     > time_low, time_mid, time_hi_and_version. The same encoding, also known as
> >>     > wire format, should also be used for the SMBIOS representation of the UUID.
> >>     >
> >>     > The UUID {00112233-4455-6677-8899-AABBCCDDEEFF} would thus be represented
> >>     > as 33 22 11 00 55 44 77 66 88 99 AA BB CC DD EE FF.
> >>
> >>     The dmidecode tool implements this and decodes the above "wire format"
> >>     when SMBIOS version >= 2.6. We moved from SMBIOS version 2.4 to 2.8 when
> >>     we started building the SMBIOS entry point inside QEMU, on commit
> >>     c97294ec1b9e36887e119589d456557d72ab37b5.
> >>
> >>
> >> seabios doesn't seem to handle this special UUID format when reading from smbios.
> > 
> > Hmm.  Changing the ordering in display_uuid() is easy.  There seems to
> > be no easy way to figure which format to use though.  Checking the
> > version like dmidecode doesn't fly as there are qemu versions with old
> > format but version smbios 2.8 in the wild ...

QEMU versions with the old format but smbios 2.8 are buggy, and
exposing a broken UUID to guests. I don't believe you need to
work around that QEMU bug in the tools that display the UUID.

That translates to:
* pc-2.2 and later report SMBIOS 2.8 and use the correct format,
  so it's OK
* pc-2.1 is buggy, because it reports SMBIOS 2.8 and use the
  old format
* pc-2.0 and older is OK, because it lets SeaBIOS build the
  SMBIOS tables, which uses the old format and reports SMBIOS 2.4

Showing the wrong UUID when using pc-2.1 seems unavoidable
(because that's a QEMU Bug). But you should be able to display
the right UUID on all other pc versions (pc <= 2.0 or pc >= 2.2).

> 
> Plus, because this is guest visible, Eduardo's patch noted above only
> changes the encoding for 2.2 and later QEMU machine types. If you run
> your reproducer but flip the machine type to 2.1 or earlier, you should
> see the UUID on the SeaBIOS screen change.

Not 2.1 or earlier, but 2.1 only. If you use 2.0 or earlier, the
UUID should be correct.

-- 
Eduardo