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

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

On 11/12/21 5:44 PM, Peter Gonda wrote:
> On Fri, Nov 12, 2021 at 4:39 PM Brijesh Singh <brijesh.singh@amd.com> wrote:
>>
>> On 11/12/21 10:55 AM, Peter Gonda wrote:
>>> On Wed, Nov 10, 2021 at 8:32 AM Peter Gonda <pgonda@google.com> wrote:
>>>> On Tue, Nov 9, 2021 at 3:20 PM Brijesh Singh <brijesh.singh@amd.com> wrote:
>>>>>
>>>>> 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 ?
>>>> Thats a good point Brijesh. I've only been testing this with SEV and
>>>> ES so haven't noticed that long setup time. I like the idea of a
>>>> module parameter to decide when to INIT, that should satisfy Sean's
>>>> concern that the user doesn't know when the INIT_EX file would be read
>>>> and that there is extra retry code (duplicated between sev_pci_init
>>>> and all the PSP commands). I'll get started on that.
>>> I need a little guidance on how to proceed with this. Should I have
>>> the new module parameter 'psp_init_on_probe' just disable PSP init on
>>> module init if false. Or should it also disable PSP init during
>>> command flow if it's true?
>>>
>>> I was thinking I should just have 'psp_init_on_probe' default to true,
>>> and if false it stops the PSP init during sev_pci_init(). If I add the
>>> second change that seems like it changes the ABI. Thoughts?
>>>
>> Good point that a module params may break the ABI. How about if we add a
>> new ioctl that can be used to initialize the SEV_INIT_EX. The ioctl
>> implementation will be similar to the PLATFORM_RESET; it will shutdown
>> the firmware then call INIT_EX. A platform provisioning tool may use ioctl.
> Would just a 'skip_psp_init_on_probe' parameter be simpler. We default
> to false but if users set it, we can skip that init attempt in
> sev_pci_init(). The init attempts on all other commands that require
> the INIT state would then provide users with INIT_EX functionality.
> They would also know exactly when INIT or INIT_EX would be attempted
> based on the parameter.

Yes, I think that option is also acceptable. Because we are requiring
the user to explicitly say that it does not want to INIT on boot.


>
> Otherwise a new ioctl sounds reasonable.
>> -Brijesh
>>