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

[Stefan Berger]

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.

    Stefan

>     }
>
>     return TPM_VERSION_1_2;
> }
>