Message-ID: <14e6c746-c7d3-8cca-47ed-b90f31e4e495@amd.com>
Date:   Fri, 12 Nov 2021 17:39:42 -0600
From:   Brijesh Singh <brijesh.singh@....com>
To:     Peter Gonda <pgonda@...gle.com>
Cc:     brijesh.singh@....com, Sean Christopherson <seanjc@...gle.com>,
        Thomas.Lendacky@....com, David Rientjes <rientjes@...gle.com>,
        Marc Orr <marcorr@...gle.com>, Joerg Roedel <jroedel@...e.de>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        John Allen <john.allen@....com>,
        "David S. Miller" <davem@...emloft.net>,
        Paolo Bonzini <pbonzini@...hat.com>,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3 4/4] crypto: ccp - Add SEV_INIT_EX support


On 11/12/21 10:55 AM, Peter Gonda wrote:
> On Wed, Nov 10, 2021 at 8:32 AM Peter Gonda <pgonda@...gle.com> wrote:
>> On Tue, Nov 9, 2021 at 3:20 PM Brijesh Singh <brijesh.singh@....com> wrote:
>>>
>>>
>>> On 11/9/21 2:46 PM, Peter Gonda wrote:
>>>> On Tue, Nov 9, 2021 at 1:26 PM Sean Christopherson <seanjc@...gle.com> wrote:
>>>>> On Tue, Nov 09, 2021, Peter Gonda wrote:
>>>>>> On Tue, Nov 9, 2021 at 10:21 AM Sean Christopherson <seanjc@...gle.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.

-Brijesh

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