Re: [PATCH v6 04/14] x86: Secure Launch Resource Table header file

From: Daniel P. Smith
Date: Mon May 15 2023 - 17:16:11 EST

On 5/12/23 06:55, Matthew Garrett wrote:
On Thu, May 04, 2023 at 02:50:13PM +0000, Ross Philipson wrote:

+#define SLR_TABLE_MAGIC 0x4452544d

From convention I'd expect this to be 0x534c5254, but not really an

Apologies, but which convention?

+/* SLR defined bootloaders */

Oof. Having the kernel know about bootloaders has not worked out super
well for us in the past. If someone writes a new bootloader, are they
unable to Secure Launch any existing kernels? The pragmatic thing for
them to do would be to just pretend they're grub, which kind of defeats
the point of having this definition...

Actually, this is not for making the kernel know about bootloaders. This is dealing with the challenge created when the preamble was split for efi-stub, and similar use cases, where what sets up the preamble, ie. the bootloader, is separate from what invokes the dynamic launch, ie. the DLE handler. The reality is that even in the simplest implementation of the DLE handler, a remnant of GRUB for call back from efi-stub, there is information that is needed to cross the gap.

+} __packed;

Random nit - why are they all packed? Are there circumstances where two
pieces of code with different assumptions about alignment will be
looking at a single instance of a table? It doesn't seem likely we're
going to be doing DRTM in a 32-bit firmware environment while launching
a 64-bit kernel?

We wrote the TrenchBoot Secure Launch general spec [1] with as much forethought as possible for the target environments. Specifically, the desire is to have a common approach for x86 (Intel and AMD), Arm, and perhaps down the road the POWER arch. In particular, I do not believe there is anything in the Arm DRTM beta spec that prohibits a mixed 32/64 bit environment. In the end it is better to for the spec to be safe for those environments then having to make changes to the spec later down the road.