[Skiboot] [PATCH] libstb/secureboot: Disable secureboot in OPAL by nvram

Claudio Carvalho cclaudio at linux.vnet.ibm.com
Fri May 11 22:54:08 AEST 2018

On 11/05/2018 09:33, ppaidipe wrote:
> On 2018-05-11 17:47, Claudio Carvalho wrote:
>> ---
>> Claudio Carvalho
>> Linux Security Development - IBM LTC
>>> ----- Original message -----
>>> From: ppaidipe <ppaidipe at linux.vnet.ibm.com>
>>> To: Nayna Jain <nayna at linux.vnet.ibm.com>
>>> Cc: skiboot at lists.ozlabs.org, George Wilson <gcwilson at us.ibm.com>,
>>> Claudio Carvalho/Brazil/IBM at IBMBR, hellerda at us.ibm.com,
>>> erichte at us.ibm.com, sarahw at us.ibm.com
>>> Subject: Re: [Skiboot] [PATCH] libstb/secureboot: Disable secureboot
>>> in OPAL by nvram
>>> Date: Fri, May 11, 2018 9:04 AM
>>> On 2018-05-11 16:52, Nayna Jain wrote:
>>>> On 05/09/2018 02:40 PM, Pridhiviraj Paidipeddi wrote:
>>>>> Currently custom debug petitboot kernels failed to boot on
>>> secureboot
>>>>> enabled systems as the key verification fails results in
>>> enforcing the
>>>>> boot. Due to which debugging any problems in petitboot kernel in
>>>>> secure
>>>>> boot enabled systems become hard.
>>>>> This patch provides a way to disable secureboot in OPAL by using
>>> below
>>>>> nvram command.
>>>> Petitboot verification should not be disabled if firmware secure
>>> boot
>>>> is on. Its only Host OS kernel
>>>> for which we can have the switch.
>>>> This patch can result in a loophole where someone as application
>>> user
>>>> can disable
>>>> verification of petitboot kernel using nvram utility.
>>> Yeah, agree, but this is really a debug hack, without that there are
>>> bugs related to keys
>>> in upstream vs vendor released firmware, due to which verification
>>> fails
>>> and boot enforce
>>> happening on secureboot enabled systems,
>> I'm not sure if I know what bug you are talking about here. Can you
>> elaborate more on that?
> Yes, Lets say p9dsu system is having latest supermicro released 
> firmware(having imprint keys)
> and secureboot mode is enabled in the system. If we compile custom 
> kernel in upstream op-build
> using development mode in signed mode and flash that on that failed 
> secureboot system. so when
> we boot with that kernel, keys verification is failing, i am not sure 
> why it is failing now, earlier
> it works when doing testing. The kernel tried from both the places one 
> is zImage.epapr and another
> one is extracted BOOTKERNEL partition from full PNOR built in signed 
> imprint mode. Using both the images
> verification is failing now.

Hmm ... as long as the system trusts the imprinting keys (not any 
production key), you should still be able to build and boot custom 
zImage.epapr signed with imprinting keys. Do you remember how you built 
(and signed) the zImage.epapr?


>> Thanks,
>> Claudio
>>> so we need a way to force
>>> disable it, like the way
>>> we have for enabling it via nvram. Otherwise debugging petitboot
>>> kernels
>>> on such systems
>>> became really hard.
>>> Thanks
>>> Pridhiviraj
>>>> Thanks & Regards,
>>>> - Nayna
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