The Hirsute Hippo has reached End of Life, so this bug will not be fixed
for that release.
** Changed in: linux (Ubuntu Hirsute)
Status: Fix Committed => Won't Fix
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https://bugs.launchpad.net/bugs/1931254
Title:
Google Confidential Compute fails to boot with shim version 1.47
Status in linux package in Ubuntu:
Fix Released
Status in linux-gcp package in Ubuntu:
Fix Released
Status in linux source package in Hirsute:
Won't Fix
Status in linux-gcp source package in Hirsute:
Fix Released
Bug description:
# Overview
Hirsute and Impish daily builds are currently not booting on Google
Confidential Compute. Confidential compute is Google's platform that
enables the use of Secure Encrypted Virtualization extension via AMD
EPYC CPUs. Booting an image with version 1.45 works, but once upgraded
to 1.47, the VM no longer boots, and instead the kernel panics.
Launching the image with secure boot, but without confidential compute
works as expected.
# Expected result
The system is able to reboot after the upgrade.
# Actual result
Kernel panic: https://paste.ubuntu.com/p/mHrvVc6qBc/
# Steps to reproduce
Launch a VM in GCE with confidential compute enabled with a serial
v20210511a or later and look at the serial log for the kernel panic.
Example CLI command to launch a VM:
$ gcloud beta compute instances create $USER-confidential-testing
--zone=us-west1-b --machine-type=n2d-standard-2 --image=daily-
ubuntu-2104-hirsute-v20210511a --image-project=ubuntu-os-cloud-devel
--confidential-compute --maintenance-policy=TERMINATE
The last known good working image is daily-
ubuntu-2104-hirsute-v20210510. The upgrade that fails is when shim
signed is updated from 1.46+15.4-0ubuntu1 to 1.47+15.4-0ubuntu2
# Logs & notes
* 20210510 manifest (good): https://paste.ubuntu.com/p/QjnMPcJj7G/
* 20210511a manifest (bad): https://paste.ubuntu.com/p/PvJQwRXHcG/
* diff between manifests: https://paste.ubuntu.com/p/4nJtGxqGn7/
* serial logs of failed boot: https://paste.ubuntu.com/p/mHrvVc6qBc/
# Cause:
shim changed the memory type for pages reserved for EFI runtime
services, from EfiRuntimeServicesData to EfiBootServicesData.
Memory reserved for EFI runtime/boot services must be remapped as
encrypted in the kernel (during boot) if SEV (secure encrypted
virtualization) is enabled. The original kernel implementation of
ioremap only correctly mapped the region as encrypted for
EfiRuntimeServicesData regions, so when shim changed the type to
EfiBootServicesData the kernel bug was exposed
Note that this affects all 5.11 kernels not just gcp. It is possible
that gcp is the only cloud that uses sev currently (for "Confidential
Computing").
# Fix:
Both EfiRuntimeServicesData and EfiBootServicesData must be mapped as
encrypted if SEV is active, as per:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=8d651ee9c71bb12fc0c8eb2786b66cbe5aa3e43b
# Test
Without the fix applied, confirmed that I was able to reproduce the issue
described here (complete failure to boot, kernel panic)
With fix, confirmed no issues booting
# Regression potential
The fix could potentially cause boot failures, if a memory region is
marked encrypted when it shouldn't be. I assume in that case it would
cause a panic similar to the one seen here for this bug:
general protection fault, probably for non-canonical address
0x314836c31124d346: 0000 [#1] SMP NOPTI
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