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I have installed tboot using this command apt-get install tboot on ubuntu . Actually I am having one doubt regarding tboot and trusted Grub. trusted grub does STRM(static root of trust for Measurement ) and it changes values in PCR 12 -PCR14. tboot does DRTM(Dynamic root of trust for Measurement ) using Trusted Execution Technology ( Intel 's TXT) technology . It will changes values in PCR17 to PCR22 .I want to know that if tboot supports SRTM then it should also change values in PCR 12 to PCR14 for different linux kernel version .But tboot is changing only For PCR17 to PCR22 for different linux kernel version . tboot can provide SRTM and DRTM both at a time??

user1710979
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1 Answers1

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No.

The SRTM is always your firmware. And tboot itself is not your DRTM either. The DRTM is the SINIT module. Tboot is responsible for preparing the late launch and after returning from the SINIT code functions as your MLE, thus extending your dynamic chain of trust.

Scolytus
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  • thanks .If I want Static root of trust ,then it is must i have to use Trusted grub or there is any alternative for SRTM? – user1710979 May 09 '14 at 06:00
  • Trusted Grub is not your SRTM, likewise. The SRTM is part of the firmware. If you want to extend the chain to the bootloader and beyound, you need a trusted computing aware chain of software. If you are on a PC platform than most probably Trusted GRUB is a good choice. But also UBoot on embedded systems is capable of taking measurements. – Scolytus May 09 '14 at 06:52
  • Also, the boot loader is the last component to be measured by the firmware. To measure components that run after the boot loader, you need to perform the DTRM. The PCRs that store the measurements of these additional components are only available through specific TPM localities. On both Intel and AMD platforms, the required locality is not accessible without an explicit trusted launch using "GETSEC SENTER" (Intel) or "SKINIT" (AMD). – Safayet Ahmed Mar 25 '15 at 13:13
  • @SafayetAhmed that's not true. While the bootloader is the last component that's measured by the firmware, it's the bootloader's responsibility to extend the chain of trust. That's why it's called a chain of trust. So your statement that you *need to perform the DRTM* is false. – Scolytus Mar 25 '15 at 22:01
  • It IS the bootloader's responsibility to extend the chain of trust. What I was referring to was the TPM PCRs. To extend PCRS associated with DRTM (PCR17 , PCR18, ...) you need to access the TPM through a specific locality. To the best of my knowledge, that locality is not accessible on Intel/AMD platforms without performing a DRTM. – Safayet Ahmed Mar 27 '15 at 19:40
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    @SafayetAhmed that's true, but you did not write this in your first comment ;) – Scolytus Mar 27 '15 at 20:05
  • Ah, this is something I was trying to get my head around. If you use SBOOT with grub or any old bootloader, then there is a broken chain, is there not? firmware measures bootloader, SINIT might measure itself and any kernels, but unless you have a bootloader that measures its kernels (i.e. sinit in this case), then there is a break in the chain, right? – deitch Apr 11 '16 at 11:15