[PATCH] tpm2: table size can be 76 when "LAML" & "LASA" are used

[Alex Hung]

On Wed, Jul 22, 2020 at 8:21 PM ivanhu <ivan.hu at canonical.com> wrote:

>
>
> On 7/23/20 2:21 AM, Alex Hung wrote:
> > TCG ACPI Specification released in 2017 added two fields, "Log Area
> > Minimum Length" and "Log Area Start Address". When they are used, the
> > table size will be 76.
> >
> > Buglink: https://bugs.launchpad.net/bugs/1888189
> >
> > Signed-off-by: Alex Hung <alex.hung at canonical.com>
> > ---
> >  src/acpi/tpm2/tpm2.c | 35 +++++++++++++++++++----------------
> >  1 file changed, 19 insertions(+), 16 deletions(-)
> >
> > diff --git a/src/acpi/tpm2/tpm2.c b/src/acpi/tpm2/tpm2.c
> > index bca5cb8a..56b35a1c 100644
> > --- a/src/acpi/tpm2/tpm2.c
> > +++ b/src/acpi/tpm2/tpm2.c
> > @@ -72,22 +72,25 @@ static int tpm2_test1(fwts_framework *fw)
> >                       tpm2->start_method);
> >       }
> >
> > -     if (tpm2->start_method == 2 && table->length !=
> sizeof(fwts_acpi_table_tpm2) + 4) {
> > -             passed = false;
> > -             fwts_failed(fw, LOG_LEVEL_HIGH,
> > -                     "TPM2BadPlatformParameters",
> > -                     "Table length must be 0x%" PRIx32 " if Start
> method equals 2, got 0x%" PRIx32,
> > -                     (uint32_t) sizeof(fwts_acpi_table_tpm2) + 4,
> > -                     (uint32_t) table->length);
> > -     }
> > -
> > -     if (tpm2->start_method == 11 && table->length <
> sizeof(fwts_acpi_table_tpm2) + 12) {
> > -             passed = false;
> > -             fwts_failed(fw, LOG_LEVEL_HIGH,
> > -                     "TPM2BadPlatformParameters",
> > -                     "Table length must be atleast 0x%" PRIx32 " if
> Start method equals 11, got 0x%" PRIx32,
> > -                     (uint32_t) sizeof(fwts_acpi_table_tpm2) + 12,
> > -                     (uint32_t) table->length);
> > +     /* When TPM2 includes fields "LAML" & "LASA", table size will be
> fixed to 76. */
> > +     if (table->length != 76) {
>
> From the Spec, we shouldn't check the fixed size 76, the Start Method
> Specific Parameters is variable, and both LAML and LASA are optional.
>
> I think we should check the sizes of Start Method Specific Parameters,
> LAML and LASA included or not.
>

That's not entirely correct.

The document (
https://trustedcomputinggroup.org/wp-content/uploads/TCG_ACPIGeneralSpecification_v1.20_r8.pdf)
states the length as below:
========================
The length of this table starting from the Signature field up to
and including the Start Method specific parameters field. (52
+ size of Start Method specific parameters)
If the table contains LAML and LASA field, Length is 76.
========================

It also states "Start Method Specific Parameters" can be varying or fixed
in size
========================
The content of the Start Method specific parameters is
determined by the Start Method....

If LAML and LASA are present, then this field is 12 bytes in size.
========================

I would interpret that the length can be 76 or variable (52 + Specific
Parameters). This is not depending on Start Method but on the availability
of LAML and LASA.

Note: This definition seems to be changed from 2013, but the table revision
did not change.


>
> Cheers,
> Ivan
>
> > +             if (tpm2->start_method == 2 && table->length !=
> sizeof(fwts_acpi_table_tpm2) + 4) {
> > +                     passed = false;
> > +                     fwts_failed(fw, LOG_LEVEL_HIGH,
> > +                             "TPM2BadPlatformParameters",
> > +                             "Table length must be 0x%" PRIx32 " if
> Start Method equals 2, "
> > +                             "got 0x%" PRIx32, (uint32_t)
> sizeof(fwts_acpi_table_tpm2) + 4,
> > +                             (uint32_t) table->length);
> > +             }
> > +
> > +             if (tpm2->start_method == 11 && table->length <
> sizeof(fwts_acpi_table_tpm2) + 12) {
> > +                     passed = false;
> > +                     fwts_failed(fw, LOG_LEVEL_HIGH,
> > +                             "TPM2BadPlatformParameters",
> > +                             "Table length must be at least 0x%" PRIx32
> " if Start Method equals 11, "
> > +                             "got 0x%" PRIx32, (uint32_t)
> sizeof(fwts_acpi_table_tpm2) + 12,
> > +                             (uint32_t) table->length);
> > +             }
> >       }
> >
> >       if (passed)
> >
>


-- 
Cheers,
Alex Hung
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