On Mon, Jun 25, 2018 at 05:00:05PM -0400, Nathaniel McCallum wrote: > On Thu, Jun 21, 2018 at 5:21 PM Sean Christopherson > <sean.j.christopherson@xxxxxxxxx> wrote: > > > > On Thu, Jun 21, 2018 at 03:11:18PM -0400, Nathaniel McCallum wrote: > > > If this is acceptable for everyone, my hope is the following: > > > > > > 1. Intel would split the existing code into one of the following > > > schemas (I don't care which): > > > A. three parts: UEFI module, FLC-only kernel driver and user-space > > > launch enclave > > > B. two parts: UEFI module (including launch enclave) and FLC-only > > > kernel driver > > > > To make sure I understand correctly... > > > > The UEFI module would lock the LE MSRs with a public key hardcoded > > into both the UEFI module and the kernel at build time? > > > > And for the kernel, it would only load its SGX driver if FLC is > > supported and the MSRs are locked to the expected key? > > > > IIUC, this approach will cause problems for virtualization. Running > > VMs with different LE keys would require the bare metal firmware to > > configure the LE MSRs to be unlocked, which would effectively make > > using SGX in the host OS mutually exlusive with exposing SGX to KVM > > guests. Theoretically it would be possible for KVM to emulate the > > guest's LE and use the host's LE to generate EINIT tokens, but > > emulating an enclave would likely require a massive amount of code > > and/or complexity. > > How is this different from any other scenario where you lock the LE > MSRs? Unless Intel provides hardware support between the LE MSRs and > the VMX instructions, I don't see any way around this besides letting > any launch enclave run. It's not. All prior discussions have effectively required unlocked MSRs, so that's my baseline. > > > 2. Intel would release a reproducible build of the GPL UEFI module > > > sources signed with a SecureBoot trusted key and provide an > > > acceptable[0] binary redistribution license. > > > > > > 3. The kernel community would agree to merge the kernel driver given > > > the above criteria (and, obviously, acceptable kernel code). > > > > > > The question of how to distribute the UEFI module and possible launch > > > enclave remains open. I see two options: independent distribution and > > > bundling it in linux-firmware. The former may be a better > > > technological fit since the UEFI module will likely need to be run > > > before the kernel (and the boot loader; and shim). However, the latter > > > has the benefit of already being a well-known entity to our downstream > > > distributors. I could go either way on this. > > > > Writing and locks the LE MSRs effectively needs to be done before > > running the bootloader/kernel/etc... Delaying activation would > > require, at a minimum, leaving IA32_FEATURE_CONTROL unlocked since > > IA32_FEATURE_CONTROL's SGX bits can't be set until SGX is activated. > > > > > I know this plan is more work for everyone involved, but I think it > > > manages to actually maximize both security and freedom. > > > > > > [0]: details here - > > > https://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux-firmware.git/tree/README#n19 > > > On Thu, Jun 21, 2018 at 11:29 AM Neil Horman <nhorman@xxxxxxxxxx> wrote: > > > > > > > > On Thu, Jun 21, 2018 at 08:32:25AM -0400, Nathaniel McCallum wrote: > > > > > On Wed, Jun 20, 2018 at 5:02 PM Sean Christopherson > > > > > <sean.j.christopherson@xxxxxxxxx> wrote: > > > > > > > > > > > > On Wed, Jun 20, 2018 at 11:39:00AM -0700, Jethro Beekman wrote: > > > > > > > On 2018-06-20 11:16, Jethro Beekman wrote: > > > > > > > > > This last bit is also repeated in different words in Table 35-2 and > > > > > > > > > Section 42.2.2. The MSRs are *not writable* before the write-lock bit > > > > > > > > > itself is locked. Meaning the MSRs are either locked with Intel's key > > > > > > > > > hash, or not locked at all. > > > > > > > > > > > > > > Actually, this might be a documentation bug. I have some test hardware and I > > > > > > > was able to configure the MSRs in the BIOS and then read the MSRs after boot > > > > > > > like this: > > > > > > > > > > > > > > MSR 0x3a 0x0000000000040005 > > > > > > > MSR 0x8c 0x20180620aaaaaaaa > > > > > > > MSR 0x8d 0x20180620bbbbbbbb > > > > > > > MSR 0x8e 0x20180620cccccccc > > > > > > > MSR 0x8f 0x20180620dddddddd > > > > > > > > > > > > > > Since this is not production hardware, it could also be a CPU bug of course. > > > > > > > > > > > > > > If it is indeed possible to configure AND lock the MSR values to non-Intel > > > > > > > values, I'm very much in favor of Nathaniels proposal to treat the launch > > > > > > > enclave like any other firmware blob. > > > > > > > > > > > > It's not a CPU or documentation bug (though the latter is arguable). > > > > > > SGX has an activation step that is triggered by doing a WRMSR(0x7a) > > > > > > with bit 0 set. Until SGX is activated, the SGX related bits in > > > > > > IA32_FEATURE_CONTROL cannot be set, i.e. SGX can't be enabled. But, > > > > > > the LE hash MSRs are fully writable prior to activation, e.g. to > > > > > > allow firmware to lock down the LE key with a non-Intel value. > > > > > > > > > > > > So yes, it's possible to lock the MSRs to a non-Intel value. The > > > > > > obvious caveat is that whatever blob is used to write the MSRs would > > > > > > need be executed prior to activation. > > > > > > > > > > This implies that it should be possible to create MSR activation (and > > > > > an embedded launch enclave?) entirely as a UEFI module. The kernel > > > > > would still get to manage who has access to /dev/sgx and other > > > > > important non-cryptographic policy details. Users would still be able > > > > > to control the cryptographic policy details (via BIOS Secure Boot > > > > > configuration that exists today). Distributions could still control > > > > > cryptographic policy details via signing of the UEFI module with their > > > > > own Secure Boot key (or using something like shim). The UEFI module > > > > > (and possibly the external launch enclave) could be distributed via > > > > > linux-firmware. > > > > > > > > > > Andy/Neil, does this work for you? > > > > > > > > > I need some time to digest it. Who in your mind is writing the UEFI module. Is > > > > that the firmware vendor or IHV? > > > > > > > > Neil > > > > > > > > > > As for the SDM, it's a documentation... omission? SGX activation > > > > > > is intentionally omitted from the SDM. The intended usage model is > > > > > > that firmware will always do the activation (if it wants SGX enabled), > > > > > > i.e. post-firmware software will only ever "see" SGX as disabled or > > > > > > in the fully activated state, and so the SDM doesn't describe SGX > > > > > > behavior prior to activation. I believe the activation process, or > > > > > > at least what is required from firmware, is documented in the BIOS > > > > > > writer's guide. > > > > > > > > > > > > > Jethro Beekman | Fortanix > > > > > > > > > > > > > > > > > > >
