Re: [PULL 5/5] crypto/tls-cipher-suites: Produce fw_cfg consumable blob

[Laszlo Ersek <lersek@redhat.com>]

On 10/05/20 11:16, Philippe Mathieu-Daudé wrote:
> Hi Laszlo,
> 
> On 10/1/20 9:18 AM, Laszlo Ersek wrote:
>> On 09/29/20 17:46, Kevin Wolf wrote:
>>> Am 04.07.2020 um 18:39 hat Philippe Mathieu-Daudé geschrieben:
>>>> Since our format is consumable by the fw_cfg device,
>>>> we can implement the FW_CFG_DATA_GENERATOR interface.
>>>>
>>>> Example of use to dump the cipher suites (if tracing enabled):
>>>>
>>>>   $ qemu-system-x86_64 -S \
>>>>     -object tls-cipher-suites,id=mysuite1,priority=@SYSTEM \
>>>>     -fw_cfg name=etc/path/to/ciphers,gen_id=mysuite1 \
>>>>     -trace qcrypto\*
>>>>   1590664444.197123:qcrypto_tls_cipher_suite_priority priority: @SYSTEM
>>>>   1590664444.197219:qcrypto_tls_cipher_suite_info data=[0x13,0x02] version=TLS1.3 name=TLS_AES_256_GCM_SHA384
>>>>   1590664444.197228:qcrypto_tls_cipher_suite_info data=[0x13,0x03] version=TLS1.3 name=TLS_CHACHA20_POLY1305_SHA256
>>>>   1590664444.197233:qcrypto_tls_cipher_suite_info data=[0x13,0x01] version=TLS1.3 name=TLS_AES_128_GCM_SHA256
>>>>   1590664444.197236:qcrypto_tls_cipher_suite_info data=[0x13,0x04] version=TLS1.3 name=TLS_AES_128_CCM_SHA256
>>>>   1590664444.197240:qcrypto_tls_cipher_suite_info data=[0xc0,0x30] version=TLS1.2 name=TLS_ECDHE_RSA_AES_256_GCM_SHA384
>>>>   1590664444.197245:qcrypto_tls_cipher_suite_info data=[0xcc,0xa8] version=TLS1.2 name=TLS_ECDHE_RSA_CHACHA20_POLY1305
>>>>   1590664444.197250:qcrypto_tls_cipher_suite_info data=[0xc0,0x14] version=TLS1.0 name=TLS_ECDHE_RSA_AES_256_CBC_SHA1
>>>>   1590664444.197254:qcrypto_tls_cipher_suite_info data=[0xc0,0x2f] version=TLS1.2 name=TLS_ECDHE_RSA_AES_128_GCM_SHA256
>>>>   1590664444.197258:qcrypto_tls_cipher_suite_info data=[0xc0,0x13] version=TLS1.0 name=TLS_ECDHE_RSA_AES_128_CBC_SHA1
>>>>   1590664444.197261:qcrypto_tls_cipher_suite_info data=[0xc0,0x2c] version=TLS1.2 name=TLS_ECDHE_ECDSA_AES_256_GCM_SHA384
>>>>   1590664444.197266:qcrypto_tls_cipher_suite_info data=[0xcc,0xa9] version=TLS1.2 name=TLS_ECDHE_ECDSA_CHACHA20_POLY1305
>>>>   1590664444.197270:qcrypto_tls_cipher_suite_info data=[0xc0,0xad] version=TLS1.2 name=TLS_ECDHE_ECDSA_AES_256_CCM
>>>>   1590664444.197274:qcrypto_tls_cipher_suite_info data=[0xc0,0x0a] version=TLS1.0 name=TLS_ECDHE_ECDSA_AES_256_CBC_SHA1
>>>>   1590664444.197278:qcrypto_tls_cipher_suite_info data=[0xc0,0x2b] version=TLS1.2 name=TLS_ECDHE_ECDSA_AES_128_GCM_SHA256
>>>>   1590664444.197283:qcrypto_tls_cipher_suite_info data=[0xc0,0xac] version=TLS1.2 name=TLS_ECDHE_ECDSA_AES_128_CCM
>>>>   1590664444.197287:qcrypto_tls_cipher_suite_info data=[0xc0,0x09] version=TLS1.0 name=TLS_ECDHE_ECDSA_AES_128_CBC_SHA1
>>>>   1590664444.197291:qcrypto_tls_cipher_suite_info data=[0x00,0x9d] version=TLS1.2 name=TLS_RSA_AES_256_GCM_SHA384
>>>>   1590664444.197296:qcrypto_tls_cipher_suite_info data=[0xc0,0x9d] version=TLS1.2 name=TLS_RSA_AES_256_CCM
>>>>   1590664444.197300:qcrypto_tls_cipher_suite_info data=[0x00,0x35] version=TLS1.0 name=TLS_RSA_AES_256_CBC_SHA1
>>>>   1590664444.197304:qcrypto_tls_cipher_suite_info data=[0x00,0x9c] version=TLS1.2 name=TLS_RSA_AES_128_GCM_SHA256
>>>>   1590664444.197308:qcrypto_tls_cipher_suite_info data=[0xc0,0x9c] version=TLS1.2 name=TLS_RSA_AES_128_CCM
>>>>   1590664444.197312:qcrypto_tls_cipher_suite_info data=[0x00,0x2f] version=TLS1.0 name=TLS_RSA_AES_128_CBC_SHA1
>>>>   1590664444.197316:qcrypto_tls_cipher_suite_info data=[0x00,0x9f] version=TLS1.2 name=TLS_DHE_RSA_AES_256_GCM_SHA384
>>>>   1590664444.197320:qcrypto_tls_cipher_suite_info data=[0xcc,0xaa] version=TLS1.2 name=TLS_DHE_RSA_CHACHA20_POLY1305
>>>>   1590664444.197325:qcrypto_tls_cipher_suite_info data=[0xc0,0x9f] version=TLS1.2 name=TLS_DHE_RSA_AES_256_CCM
>>>>   1590664444.197329:qcrypto_tls_cipher_suite_info data=[0x00,0x39] version=TLS1.0 name=TLS_DHE_RSA_AES_256_CBC_SHA1
>>>>   1590664444.197333:qcrypto_tls_cipher_suite_info data=[0x00,0x9e] version=TLS1.2 name=TLS_DHE_RSA_AES_128_GCM_SHA256
>>>>   1590664444.197337:qcrypto_tls_cipher_suite_info data=[0xc0,0x9e] version=TLS1.2 name=TLS_DHE_RSA_AES_128_CCM
>>>>   1590664444.197341:qcrypto_tls_cipher_suite_info data=[0x00,0x33] version=TLS1.0 name=TLS_DHE_RSA_AES_128_CBC_SHA1
>>>>   1590664444.197345:qcrypto_tls_cipher_suite_count count: 29
>>>>
>>>> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
>>>> Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
>>>> Acked-by: Laszlo Ersek <lersek@redhat.com>
>>>> Message-Id: <20200623172726.21040-6-philmd@redhat.com>
>>>
>>> I noticed only now that this breaks '--object help' in
>>> qemu-storage-daemon:
>>>
>>> $ qemu-storage-daemon --object help
>>> List of user creatable objects:
>>> qemu-storage-daemon: missing interface 'fw_cfg-data-generator' for object 'tls-creds'
>>> Aborted (core dumped)
>>>
>>> The reason is that we don't (and can't) link hw/nvram/fw_cfg.c into the
>>> storage daemon because it requires other system emulator stuff.
>>
>> Ouch. I've been completely oblivious to "--object help" and how it
>> affects qemu-storage-daemon. Sorry about that.
>>
>> Could you please include a backtrace about the abort()?
>>
>> Grepping for the error message, I can find type_initialize() in
>> "qom/object.c", but my knowledge about QOM internals is practically nil.
>>
>> The error message seems bogus FWIW -- why would
>> TYPE_FW_CFG_DATA_GENERATOR_INTERFACE be *required* from "tls-creds"?
>>
>> TYPE_FW_CFG_DATA_GENERATOR_INTERFACE is implemented by
>> "tls-cipher-suites", and required by "-fw_cfg name=...,gen_id=...". If
>> that -fw_cfg switch is not used, then why would anything look for the
>> TYPE_FW_CFG_DATA_GENERATOR_INTERFACE interface? Especially under the
>> tls-creds object?
> 
> Sorry for not updating Kevin's post in time (we have been discussing
> over IRC).
> 
> What happens here is a QOM design flow, first triggered by fw_cfg as
> we are now trying to have QEMU split into more components.
> 
> QOM interface/object type names are simple strings, so we don't get
> any link failure in case of missing dependency (which are resolved at
> runtime using strcmp).
> 
> "tls-cipher-suites" is a generic crypto object, it happens to implement
> the fw_cfg-data-generator interface. The fw_cfg-data-generator interface
> is registered as QOM type in hw/nvram/fw_cfg.c which is only built when
> SOFTMMU is selected. qemu-storage-daemon doesn't select SOFTMMU.
> We don't want to restrict "tls-cipher-suites" to SOFTMMU.
> 
> The simplest fix we discuss is to have a single C file to register the
> fw_cfg-data-generator interface in QOM, and link with it if any of
> CRYPTO / NVRAM kconfig is selected.
> 
> I'll send a patch.

Thank you for the explanation!

(I suggest keeping such discussions *originally* on the list. IRC is
practically indistinguishable from the bit bucket, and you'll have to
write up a summary for others on the mailing list anyway. (In some cases
it could even require filing a ticket in some tracker, in the end.) Best
to have the discussion at once on the list. Just my suggestion of course.)

Thanks!
Laszlo