[PATCH v3 0/7] efi: CapsuleUpdate: support for dynamic UUIDs

[Ilias Apalodimas]

Hi Vincent,

[...]

> > >   $ uuid -d 935FE837-FAC8-4394-C008-737D8852C60D
> > >   encode: STR:     935fe837-fac8-4394-c008-737d8852c60d
> > >           SIV:     195894493536133784175416063449172723213
> > >   decode: variant: reserved (Microsoft GUID)
> > >           version: 4 (random data based)
> > >           content: 93:5F:E8:37:FA:C8:03:94:00:08:73:7D:88:52:C6:0D
> > >                    (no semantics: random data only)
> > >
> > > A reserved Microsoft GUID variant does not look right.
> >
> > This seems like an existing bug. RFC4122 defines the MS reserved GUIDs
> > in the variant as
> > 1     1     0    Reserved, Microsoft Corporation backward
> > compatibility and the existing UUID_VARIANT_MASK is defined as 0xc0...
>
> I think the variant mask 0xc0 is correct:
>
> - The variant field is in the top three bits of the "clock seq high and
>   reserved" byte, but...
> - The variant we want is 1 0 x (do not care for bit 5, a.k.a. "Msb2").
>
> With the mask 0xc0 we can clear the top two bits as we set the top most bit just
> after anyway.
>
> ...the mask needs to be used correctly, though; see below.

Ah yes, the current code is using it in clrsetbits_8, which inverts it
internally, so it's indeed correct.

>
> >
> > The patch below should work for you (on top of Calebs')
> >
> > diff --git a/include/uuid.h b/include/uuid.h
> > index b38b20d957ef..78ed5839d2d6 100644
> > --- a/include/uuid.h
> > +++ b/include/uuid.h
> > @@ -81,7 +81,7 @@ struct uuid {
> >  #define UUID_VERSION_SHIFT     12
> >  #define UUID_VERSION           0x4
> >
> > -#define UUID_VARIANT_MASK      0xc0
> > +#define UUID_VARIANT_MASK      0xb0
> >  #define UUID_VARIANT_SHIFT     7
> >  #define UUID_VARIANT           0x1
> >
> > diff --git a/lib/uuid.c b/lib/uuid.c
> > index 89911b06ccc0..73251eaa397e 100644
> > --- a/lib/uuid.c
> > +++ b/lib/uuid.c
> > @@ -411,9 +411,9 @@ void gen_uuid_v5(const struct uuid *namespace,
> > struct uuid *uuid, ...)
> >         memcpy(uuid, hash, sizeof(*uuid));
> >
> >         /* Configure variant/version bits */
> > -       tmp = be32_to_cpu(uuid->time_hi_and_version);
> > +       tmp = uuid->time_hi_and_version;
>
> Not caring for the endianness at all does not look right.
> Indeed, while this does work on my side in little-endian, this does not work on
> on big-endian simulators.

Yes, we need the conversions

> Also, this is a 16b quantity, not 32b; we need to redefine tmp to uint16_t and
> use the be16 functions.
>

Yep I already pointed that out earlier.

> >         tmp = (tmp & ~UUID_VERSION_MASK) | (5 << UUID_VERSION_SHIFT);
> > -       uuid->time_hi_and_version = cpu_to_be32(tmp);
> > +       uuid->time_hi_and_version = tmp;
> >
> >         uuid->clock_seq_hi_and_reserved &= UUID_VARIANT_MASK;
>
> We need to mask with ~UUID_VARIANT_MASK, I think.
>
> >         uuid->clock_seq_hi_and_reserved |= UUID_VARIANT << UUID_VARIANT_SHIFT;
> >
> > Can you give it a shot?
>
> This does indeed work on my little-endian machines, but not on big-endian
> simulators.
> For testing on big-endian, I suggest using only genguid as the sandbox will not
> help there:
>
>   $ make sandbox_defconfig
>   $ make tools-only
>   $ ./tools/genguid 2a5aa852-b856-4d97-baa9-5c5f4421551f \
>         -c "qcom,qrb4210-rb2" \
>         QUALCOMM-UBOOT
>
> ...and feed the resulting UUID to `uuid -d'.
> (The genguid command is the online help example.)
>
> > What I am afraid of is breaking existing use cases using a different
> > variant mask....
> > If that's the case we might need to keep the buggy existing
> > UUID_VARIANT_MASK and use the new one only on v5 and newer code
>
> I tried to debug further and I suspect that:
>
> - Operations on 8b clock_seq_hi_and_reserved might need further casts.
>
> - My understanding is that we are generating the v5 UUID as big-endian in
>   memory; if this is indeed the case, genguid should not print it with the GUID
>   byte order.

RFC4122 says that
"put name space ID in network byte order so it hashes the same no
matter what endian machine we're on "
the EFI spec says
"It should also be noted that TimeLow, TimeMid, TimeHighAndVersion
fields in the EFI are encoded as little endian. The following table
defines the format of an EFI GUID (128 bits)."

Which is lovely....

I'll send a patch with the changes

Regards
/Ilias
>
> For the moment I am unable to make the code work in all the following cases:
>
> - genguid on little-endian
> - genguid on big-endian
> - sandbox ESRT on little-endian
>
> I will let you and Caleb know if I make any progress.
>
> Best regards,
> Vincent.
>
> >
> > Thanks
> > /Ilias