Re: [PATCH V3 4/4] crypto: ccp - Add SEV_INIT_EX support

[Brijesh Singh <brijesh.singh@amd.com>]

On 11/9/21 2:46 PM, Peter Gonda wrote:
> On Tue, Nov 9, 2021 at 1:26 PM Sean Christopherson <seanjc@google.com> wrote:
>>
>> On Tue, Nov 09, 2021, Peter Gonda wrote:
>>> On Tue, Nov 9, 2021 at 10:21 AM Sean Christopherson <seanjc@google.com> wrote:
>>>> There's no need for this to be a function pointer, and the duplicate code can be
>>>> consolidated.
>>>>
>>>> static int sev_do_init_locked(int cmd, void *data, int *error)
>>>> {
>>>>          if (sev_es_tmr) {
>>>>                  /*
>>>>                   * Do not include the encryption mask on the physical
>>>>                   * address of the TMR (firmware should clear it anyway).
>>>>                   */
>>>>                  data.flags |= SEV_INIT_FLAGS_SEV_ES;
>>>>                  data.tmr_address = __pa(sev_es_tmr);
>>>>                  data.tmr_len = SEV_ES_TMR_SIZE;
>>>>          }
>>>>          return __sev_do_cmd_locked(SEV_CMD_INIT, &data, error);
>>>> }
>>>>
>>>> static int __sev_init_locked(int *error)
>>>> {
>>>>          struct sev_data_init data;
>>>>
>>>>          memset(&data, 0, sizeof(data));
>>>>          return sev_do_init_locked(cmd, &data, error);
>>>> }
>>>>
>>>> static int __sev_init_ex_locked(int *error)
>>>> {
>>>>          struct sev_data_init_ex data;
>>>>
>>>>          memset(&data, 0, sizeof(data));
>>>>          data.length = sizeof(data);
>>>>          data.nv_address = __psp_pa(sev_init_ex_nv_address);
>>>>          data.nv_len = NV_LENGTH;
>>>>          return sev_do_init_locked(SEV_CMD_INIT_EX, &data, error);
>>>> }
>>>
>>> I am missing how this removes the duplication of the retry code,
>>> parameter checking, and other error checking code.. With what you have
>>> typed out I would assume I still need to function pointer between
>>> __sev_init_ex_locked and __sev_init_locked. Can you please elaborate
>>> here?
>>
>> Hmm.  Ah, I got distracted between the original thought, the realization that
>> the two commands used different structs, and typing up the above.
>>
>>> Also is there some reason the function pointer is not acceptable?
>>
>> It's not unacceptable, it would just be nice to avoid, assuming the alternative
>> is cleaner.  But I don't think any alternative is cleaner, since as you pointed
>> out the above is a half-baked thought.
> 
> OK I'll leave as is.
> 
>>
>>>>> +     rc = init_function(error);
>>>>>        if (rc && *error == SEV_RET_SECURE_DATA_INVALID) {
>>>>>                /*
>>>>>                 * INIT command returned an integrity check failure
>>>>> @@ -286,8 +423,8 @@ static int __sev_platform_init_locked(int *error)
>>>>>                 * failed and persistent state has been erased.
>>>>>                 * Retrying INIT command here should succeed.
>>>>>                 */
>>>>> -             dev_dbg(sev->dev, "SEV: retrying INIT command");
>>>>> -             rc = __sev_do_cmd_locked(SEV_CMD_INIT, &data, error);
>>>>> +             dev_notice(sev->dev, "SEV: retrying INIT command");
>>>>> +             rc = init_function(error);
>>>>
>>>> The above comment says "persistent state has been erased", but __sev_do_cmd_locked()
>>>> only writes back to the file if a relevant command was successful, which means
>>>> that rereading the userspace file in __sev_init_ex_locked() will retry INIT_EX
>>>> with the same garbage data.
>>>
>>> Ack my mistake, that comment is stale. I will update it so its correct
>>> for the INIT and INIT_EX flows.
>>>>
>>>> IMO, the behavior should be to read the file on load and then use the kernel buffer
>>>> without ever reloading (unless this is built as a module and is unloaded and reloaded).
>>>> The writeback then becomes opportunistic in the sense that if it fails for some reason,
>>>> the kernel's internal state isn't blasted away.
>>>
>>> One issue here is that the file read can fail on load so we use the
>>> late retry to guarantee we can read the file.
>>
>> But why continue loading if reading the file fails on load?
>>
>>> The other point seems like preference. Users may wish to shutdown the PSP FW,
>>> load a new file, and INIT_EX again with that new data. Why should we preclude
>>> them from that functionality?
>>
>> I don't think we should preclude that functionality, but it needs to be explicitly
>> tied to a userspace action, e.g. either on module load or on writing the param to
>> change the path.  If the latter is allowed, then it needs to be denied if the PSP
>> is initialized, otherwise the kernel will be in a non-coherent state and AFAICT
>> userspace will have a heck of a time even understanding what state has been used
>> to initialize the PSP.
> 
> If this driver is builtin the filesystem will be unavailable during
> __init. Using the existing retries already built into
> sev_platform_init() also the file to be read once userspace is
> running, meaning the file system is usable. As I tried to explain in
> the commit message. We could remove the sev_platform_init call during
> sev_pci_init since this only actually needs to be initialized when the
> first command requiring it is issues (either reading some keys/certs
> from the PSP or launching an SEV guest). Then userspace in both the
> builtin and module usage would know running one of those commands
> cause the file to be read for PSP usage. Tom any thoughts on this?
> 

One thing to note is that if we do the INIT on the first command then 
the first guest launch will take a longer. The init command is not 
cheap (especially with the SNP, it may take a longer because it has to 
do all those RMP setup etc). IIRC, in my early SEV series in I was doing 
the INIT during the first command execution and based on the 
recommendation moved to do the init on probe.

Should we add a module param to control whether to do INIT on probe or 
delay until the first command ?

-Brijesh