Linked by Thom Holwerda on Fri 22nd Jun 2012 23:17 UTC
Ubuntu, Kubuntu, Xubuntu After Fedora, Ubuntu has now also announced how it's going to handle the nonsense called "Secure" Boot. The gist: they'll use the same key as Fedora, but they claim they can't use GRUB2. "In the event that a manufacturer makes a mistake and delivers a locked-down system with a GRUB 2 image signed by the Ubuntu key, we have not been able to find legal guidance that we wouldn't then be required by the terms of the GPLv3 to disclose our private key in order that users can install a modified boot loader. At that point our certificates would of course be revoked and everyone would end up worse off." So, they're going to use the more liberally licensed efilinux loader from Intel. Only the bootloader will be signed; the kernel will not.
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The solution[tm]...
by pepper on Sat 23rd Jun 2012 07:56 UTC
pepper
Member since:
2007-09-18

Can someone explain to me why they don't implement a Damn Simple Bootloader in the MBR that is signed and chainloads grub2 from the currently active partition?

Also, why on earth does it seem like none of the UEFI designers ever heard of Trusted Boot? This would be the obvious solution for measuring exactly what you're loading, but reacting on it only later on after sufficient infrastructure is loaded to flexibly detect the situation(online revocation etc). At the same time, it allows anyone who doesn't care to load anything they want.

For those who don't like TPMs, UEFI can implement the necessary base function in software.

Reply Score: 3

RE: The solution[tm]...
by vaette on Sat 23rd Jun 2012 10:15 in reply to "The solution[tm]..."
vaette Member since:
2008-08-09

Making a signed bootloader that chainloads into an unsigned bootloader would break Secure Boot completely since malware makers would just install your signed bootloader and have it chainload into their unsigned malware (which in turn will set up various hooks then load the OS in a controlled way). This is also the reason why it seems improbable that Ubuntu will be able to do what they are planning to do, since loading a unsigned kernel amounts to chainloading. Malware makers will be able to use Ubuntus signed bootloader and have it launch what looks like an Ubuntu Linux kernel, but which is actually a small piece of malware that just installs hooks and then launches Windows, faking a secure boot.

Trusted Boot does not, as far as I can tell. Load sufficiently early, if a piece of malware manages to write to the MBR it will just refrain from running Trusted Boot and instead load the OS in an insecure way itself.

Edited 2012-06-23 10:16 UTC

Reply Parent Score: 3

RE[2]: The solution[tm]...
by pepper on Sat 23rd Jun 2012 16:05 in reply to "RE: The solution[tm]..."
pepper Member since:
2007-09-18

Making a signed bootloader that chainloads into an unsigned bootloader would break Secure Boot completely


As you point out, this is equivalent to chainloading an unverified kernel. So its the same security level as the proposed Ubuntu solution, but you can easily implement it and don't have to drop the most mature and flexible bootloader out there.

Trusted Boot does not, as far as I can tell, load
sufficiently early, if a piece of malware manages to
write to the MBR


No, trusted boot is started by the initial BIOS and in fact also measures extended BIOS firmware. So its in fact "earlier" than Secure Boot. And it gives you actual evidence of what happened. And it gives you an option to do something about it, instead of just stop booting. And it does not need a revocation infrastructure in the BIOS/UEFI.

Trusted Boot was specifically invented because Secure Boot is unsuitable for general-purpose PCs, where there are multiple parties that can determine what is "legitimate" and what not (you, your company, your vendor, ...).

With a system like UEFI and/or SMM, you could even let the TPM chip be implement in software by the BIOS. Still same security level as UEFI/secure boot but much more flexible and also more powerful.

Reply Parent Score: 2