[SeaBIOS] [PATCH v9 1/6] Add an implementation of a TPM TIS driver

[Stefan Berger]

On 03/21/2015 10:38 PM, Kevin O'Connor wrote:
> On Sat, Mar 21, 2015 at 09:39:57PM -0400, Stefan Berger wrote:
>> On 03/20/2015 08:59 PM, Kevin O'Connor wrote:
>>> On Fri, Mar 20, 2015 at 02:00:36PM -0400, Stefan Berger wrote:
>>>> From: Stefan Berger <stefann at linux.vnet.ibm.com>
>>>>
>>>> This patch adds an implementation of a TPM TIS driver for the TPM TIS
>>>> emulation supported by QEMU. The driver is broken up into several
>>>> small functions that have to be called in proper sequence. The driver is
>>>> cleanly separated from the rest of the code through an interface holding
>>>> pointers to the driver's functions.
>>>> A client using this driver first probes whether the TPM TIS
>>>> interface is available (probe function) and then invokes the interface
>>>> function to initialze the interface and send requests and receive responses.
>>> [...]
>>>> +struct tpm_driver tpm_drivers[TPM_NUM_DRIVERS] = {
>>>> +    [TIS_DRIVER_IDX] =
>>>> +        {
>>>> +            .timeouts      = NULL,
>>>> +            .durations     = NULL,
>>>> +            .set_timeouts  = set_timeouts,
>>>> +            .probe         = tis_probe,
>>>> +            .init          = tis_init,
>>>> +            .activate      = tis_activate,
>>>> +            .ready         = tis_ready,
>>>> +            .senddata      = tis_senddata,
>>>> +            .readresp      = tis_readresp,
>>>> +            .waitdatavalid = tis_waitdatavalid,
>>>> +            .waitrespready = tis_waitrespready,
>>>> +            .sha1threshold = 100 * 1024,
>>>> +        },
>>>> +};
>>> Can any of the above functions be called after SeaBIOS finishes its
>>> POST phase?  If so, I think the function pointers may confuse the
>>> build's detection of runtime vs init only code.
>> These functions can be called until the very end, even when the bootloaded
>> (trusted grub) calls the BIOS API. I haven't seen any crashes that
>> presumably would happen due to the memory of the table getting reused. How
>> can we make sure that this table stays alive during runtime?
> If the table itself is referenced by "runtime code" then it should be
> okay.  You can check to see that the table and its associated
> functions are not between code32init_start and code32init_end (by
> looking at out/romlayout32flat.lds or an objdump of the rom).

The above functions and the table seem to be outside that area.

     Stefan

>
> If, however, a pointer to the table (or one of the funcs) is copied to
> some struct during init and the only "runtime" references are via that
> copied pointer, then that could confuse the build check.
>
> -Kevin
>