some frequently asked questions, with draft answers

FAQ.md

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+Frequently Asked Questions about Heads
+===
+
+Why replace UEFI with coreboot?
+---
+While Intel's edk2 tree that is the base of UEFI firmware is open source,
+the firmware that vendors install on their machines is proprietary and
+closed source.  Updates for bugs fixes or security vulnerabilities
+are at the vendor's convienence; user specific enhancements are likely not
+possible; and the code is not auditable.
+
+UEFI is much more complex than the BIOS that it replaced.  It consists of
+millions of lines of code and is an entire operating system,
+with network device drivers, graphics, USB, TCP, https, etc, etc, etc.
+All of these features represents increased "surface area" for attacks,
+as well as unnecessary complexity in the boot process.
+
+coreboot is open source and focuses on just the code necessary to bring
+the system up from reset.  This minimal code base has a much smaller
+surface area and is possible to audit.  Additionally, self-help is
+possible if custom features are required or if a security vulnerability
+needs to be patched.
+
+
+What's wrong with UEFI Secure Boot?
+---
+Can't audit it, signing keys are controlled by vendors,
+doesn't handle hand off in all cases, depends on possible leaked keys.
+
+
+Why use Linux instead of vboot2?
+---
+vboot2 is part of the coreboot tree and is used by Google in the
+Chromebook system to provide boot time security by verifying the
+hashes on the coreboot payload.  This works well for the specialized
+Chrome OS on the Chromebook, but is not as flexible as a measured
+boot solution.
+
+By moving the verification into the boot scripts we're able to have
+a much flexible verification system and use more common tools like PGP
+to sign firmware stages.
+
+
+What about Trusted GRUB?
+---
+The mainline grub doesn't have support for TPM and signed kernels, but
+there is a Trusted grub fork that does.  Due to philosophical differences
+the code might not be merged into the mainline.  And due to problems
+with secure boot (which Trusted Grub builds on), many distributions have
+signed insecure kernels that bypass all of the protections secure
+boot promised.
+
+Additionally, grub is closer to UEFI in that it must have device
+drivers for all the different boot devices, as well as filesystems.
+This duplicates the code that exists in the Linux kernel and has its
+own attack surface.
+
+Using coreboot and Linux as a boot loader allows us to restrict
+the signature validation to keys that we control.  We also have one code
+base for the device drivers in the Linux-as-a-boot-loader as well
+as Linux in the operating system.
+
+
+What is the concern with the Intel Management Engine?
+---
+"Rootkit in your chipset", "x86 considered harmful", etc
+
+
+How about the other embedded devices in the system?
+---
+#goodbios, funtenna, etc.
+
+
+Should we be concerned about the binary blobs?
+---
+Maybe.  x230 has very few (MRC) since it has native vga init.
+
+
+Why use ancient Thinkpads instead of modern Macbooks?
+---
+coreboot support, TPM, nice keyboards, cheap to experiment on.
+
+How likely are physical presence attacks vs remote software attacks?
+---
+Who knows.
+
+
+Defense in depth vs single layers
+---
+Yes.
+
+is it worth doing the hardware modifications?
+---
+Depends on your threat model.
+
+
+Should I validate the TPMTOTP on every boot?
+---
+Probably.  I want to make it also do it at S3.
+
+
+suspend vs shutdown?
+---
+S3 is subject to cold boot attacks, although they are harder to
+pull off on a Heads system since the boot devices are constrained.
+
+However, without tpmtotp in s3 it is hard to know if the system is in
+a safe state when the xscreensaver lock screen comes up.  Is it a fake
+to deceive you and steal your login password?  Maybe!  It wouldn't get
+your disk password, which is perhaps an improvement.
+
+
+Disk key in TPM or user passphrase?
+---
+Depends on your threat model.  With the disk key in the TPM an attacker
+would need to have the entire machine (or a backdoor in the TPM)
+to get the key and their attempts to unlock it can be rate limited
+by the TPM hardware.
+
+However, this ties the disk to that one machine (without having to
+recover and type in the master key), which might be an unacceptable risk
+for some users.