[SeaBIOS] [PATCH 3/3] tpm: Support 2.0 TPM devices connected to a TIS host

[Stephen Douthit]

On 02/27/2018 12:17 PM, Stefan Berger wrote:
> On 02/27/2018 12:14 PM, Stephen Douthit wrote:
>> On 02/26/2018 07:45 PM, Stefan Berger wrote:
>>> On 02/26/2018 06:24 PM, Stephen Douthit wrote:
>>>> On 02/26/2018 06:02 PM, Stefan Berger wrote:
>>>>> On 02/26/2018 05:44 PM, Stephen Douthit wrote:
>>>>>> On 02/26/2018 05:09 PM, Stefan Berger wrote:
>>>>>>> On 02/26/2018 03:37 PM, Stephen Douthit wrote:
>>>>>>>> tis_get_tpm_version() was returning the interface version, which is always
>>>>>>>> 1.2 since tis_probe() would have failed if the interface wasn't TIS.
>>>>>>>>
>>>>>>>> New version check is based on the tpm2_probe() function from the Linux
>>>>>>>> tpm_tis driver.
>>>>>>>>
>>>>>>>> Signed-off-by: Stephen Douthit <stephend at silicom-usa.com>
>>>>>>>> Tested-by: Stephen Douthit <stephend at silicom-usa.com>
>>>>>>>> ---
>>>>>>>>   src/hw/tpm_drivers.c | 21 +++++++++++++++------
>>>>>>>>   src/std/tcg.h        |  1 +
>>>>>>>>   src/tcgbios.c        |  2 +-
>>>>>>>>   src/tcgbios.h        |  4 ++++
>>>>>>>>   4 files changed, 21 insertions(+), 7 deletions(-)
>>>>>>>>
>>>>>>>> diff --git a/src/hw/tpm_drivers.c b/src/hw/tpm_drivers.c
>>>>>>>> index 789d70a..32c34df 100644
>>>>>>>> --- a/src/hw/tpm_drivers.c
>>>>>>>> +++ b/src/hw/tpm_drivers.c
>>>>>>>> @@ -11,6 +11,7 @@
>>>>>>>>   #include "config.h" // CONFIG_TPM_TIS_SHA1THRESHOLD
>>>>>>>>   #include "hw/tpm_drivers.h" // struct tpm_driver
>>>>>>>>   #include "std/tcg.h" // TCG_RESPONSE_TIMEOUT
>>>>>>>> +#include "tcgbios.h" // tpm20_getcapability
>>>>>>>>   #include "output.h" // warn_timeout
>>>>>>>>   #include "stacks.h" // yield
>>>>>>>>   #include "string.h" // memcpy
>>>>>>>> @@ -119,7 +120,7 @@ static u32 tis_probe(void)
>>>>>>>>       if ((didvid != 0) && (didvid != 0xffffffff))
>>>>>>>>           rc = 1;
>>>>>>>>
>>>>>>>> -    /* TPM 2 has an interface register */
>>>>>>>> +    /* Low 32 bits of CRB interface register overlap TIS interface register */
>>>>>>>>       u32 ifaceid = readl(TIS_REG(0, TIS_REG_IFACE_ID));
>>>>>>>
>>>>>>> Since this is tis_probe, I don't think we need to mention the CRB here ...
>>>>>>
>>>>>> I think that was a note to myself I forgot to strip out when I
>>>>>> dropped my debug prints.  I'll change the comment back.
>>>>>>
>>>>>>>>
>>>>>>>>       if ((ifaceid & 0xf) != 0xf) {
>>>>>>>> @@ -142,13 +143,21 @@ static u32 tis_probe(void)
>>>>>>>>
>>>>>>>>   static TPMVersion tis_get_tpm_version(void)
>>>>>>>>   {
>>>>>>>> -    /* TPM 2 has an interface register */
>>>>>>>> -    u32 ifaceid = readl(TIS_REG(0, TIS_REG_IFACE_ID));
>>>>>>>> +    u8 buffer[128];
>>>>>>>> +    int ret;
>>>>>>>> +    struct tpm2_res_getcapability *trg =
>>>>>>>> +      (struct tpm2_res_getcapability *)&buffer;
>>>>>>>> +
>>>>>>>> +    ret = tpm20_getcapability(TPM2_CAP_TPM_PROPERTIES, cpu_to_be32(0x100),
>>>>>>>> +                              cpu_to_be32(1), &trg->hdr, sizeof(buffer));
>>>>>>>> +    if (ret == TPM2_RC_INITIALIZE)
>>>>>>>> +        return TPM_VERSION_2;
>>>>>>>> +    else if (ret)
>>>>>>>> +        return TPM_VERSION_NONE;
>>>>>>> I haven't tried yet, but likely this will not work for TPM 1.2 since it will also return an error.
>>>>>>
>>>>>> Doh.  That makes sense.  I'll need to find a 1.2 system to test on to
>>>>>> avoid stupid mistakes like that.
>>>>>>
>>>>>>> Wouldn't the check for the tag below not be sufficient? We are doing something similar in QEMU when probing for the TPM. Here we send TPM 2 command TPM_CC_ReadClock and check the tag for TPM 2 type and then TPM 1.2 command TPM_ORD_GetTicks and check for TPM 1.2 tag.
>>>>>>
>>>>>> It might be, it wasn't clear to me if the tag could be trusted if the
>>>>>> return code wasn't success.  The Linux tpm2_probe() code bails before
>>>>>> the tag comparison if tpm_transmit_cmd() returns an error.
>>>>>>
>>>>>> Is there a block of QEMU code you would recommend as a reference for
>>>>>> probing TPMs?  I'm not very familiar with that code base, and a
>>>>>> pointer would be handy.
>>>>>
>>>>> https://github.com/stefanberger/qemu-tpm/blob/v2.4.1%2Btpm/hw/tpm/tpm_util.c#L94
>>>>>
>>>>> What I don't like about the sending of commands is that we're breaking the layer here. We basically cannot send commands using this higher level API. The lowest we could go would be to call tpmhw_transmit, but that function cannot be used as it is but has to be split up to take tpm_driver as a parameter. You would pass to it &tpm_drivers[TIS_DRIVER_INDEX].
>>>>>
>>>>> As far as I know, TPM 1.2 didn't have that register, so they either return static 0 or 0xffffffff in that register.
>>>>>
>>>>> Though if reading the flags from the interface register really turns out to be insufficient, I think you should try to send a command like TPM2_CC_ReadClock. If you get back a TPM2_ST_NO_SESSION, it's a TPM 2. If you get a TPM_TAG_RSP_COMMAND it's a TPM 12.
>>>>
>>>> Thanks for all the info.  This gives me some experiments to run, and
>>>> I'll try to find a solution that avoids sending commands if possible.
>>>
>>> The following document on pdf page 100 defines bits 28-30 of the interface capability register. If the value there is 0x3 (mask 0x7), we should be sure to have a TPM 2. Hopefully that's sufficient also for your device for determining that it's a TPM 2.
>>>
>>> https://trustedcomputinggroup.org/wp-content/uploads/TCG_PC_Client_Platform_TPM_Profile_PTP_Specification_Family_2.0_Revision_1.3v22.pdf
>>>
>>>
>>
>> My interface ID reads as 0xffffffff, and the interface capability
>> register reads as intf_cap 0x30000697.  So your suggestion of
>> checking for 3 in that bitfield of the interface capability register
>> works here.
>>
>> If I change the version check function to the following and drop all
>> the other changes from patch 3/3 would that be acceptable?
>>
>> static TPMVersion tis_get_tpm_version(void)
>> {
>>     u32 reg = readl(TIS_REG(0, TIS_REG_IFACE_ID));
>>
>>     /* FIFO interface as defined in PTP for TPM 2.0 is active */
>>     if ((reg & 0xf) == 0) {
>>         return TPM_VERSION_2;
>>     }
>>     /*
>>      * FIFO interface as defined in TIS1.3 is active
>>      * Interface capabilities are defined in TIS_REG_INTF_CAPABILITY
>>      */
>>     else if ((reg & 0xf) == 0xf) {
>>         reg = readl(TIS_REG(0, TIS_REG_INTF_CAPABILITY));
>>         /* Interface 1.3 for TPM 2.0 */
>>         if (((reg >> 28) & 0x7) == 3)
>>             return TPM_VERSION_2;
> 
> 
> I think this is actually the better test and you should put this one up front.

By "up front" do you want me to swap the order of if/else if tests,
or make this the first patch in the series?

>     Stefan
> 
>>     }
>>
>>     return TPM_VERSION_1_2;
>> }
>>
>