Multiple Kexec in AWS Nitro instances fail
Affects | Status | Importance | Assigned to | Milestone | |
---|---|---|---|---|---|
linux (Ubuntu) |
Fix Released
|
High
|
Guilherme G. Piccoli | ||
Xenial |
Fix Released
|
High
|
Guilherme G. Piccoli | ||
Bionic |
Fix Released
|
High
|
Guilherme G. Piccoli | ||
Eoan |
Fix Released
|
High
|
Guilherme G. Piccoli | ||
Focal |
Fix Released
|
High
|
Guilherme G. Piccoli |
Bug Description
[Impact]
* Currently, users cannot perform multiple kernel kexec loads on AWS Nitro instances (KVM-based); after the 2nd or 3rd kexec, an initrd corruption is observed, with the following signature:
Initramfs unpacking failed: junk within compressed archive
[...]
Kernel panic - not syncing: No working init found.
Try passing init= option to kernel. See Linux Documentation/
CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.5.0-rc7-gpiccoli+ #26 Hardware name: Amazon EC2 t3.large/, BIOS 1.0 10/16/2017
Call Trace:
dump_
? csum_partial_
panic+0x101/0x2e3
? do_execve+0x25/0x30
? rest_init+0xb0/0xb0
kernel_
ret_from_
* After investigation (see comment 2), it was noticed the Amazon ena network driver doesn't provide a shutdown() handler, hence it could be performing a DMA transaction to a previous valid address during boot, which would then corrupt kernel memory. The following patch was proposed and fixed the issue, allowing 1000 kexecs to be executed successfully with no issues observed: 428c491332bc("net: ena: Add PCI shutdown handler to allow safe kexec") [ git.kernel.
* Hence, we are hereby requesting SRU for this patch. It was tested in all supported series (4.4, 4.15 and 5.3) in Amazon Nitro instances with success, and reviewed/acked by ena driver team and a kexec developer from other distro. Worth mentioning that we proposed an upstream multi-vendor discussion about this issue: marc.info/
[Test case]
* The basic test procedure is about performing multiple kexecs sequentially; AWS does not provide a full console, so in case of failures one could check the instance screenshot or use pstore/ramoops in order to collect dmesg after a crash in a preserved memory area. The commands used to perform kexec are:
kexec -l <kernel file> --initrd <initrd file> --reuse-cmdline
systemctl kexec
Alternatively, one could user "--append=" instead of "--reuse-cmdline" if a change in kexec command-line is desired; also, to execute the kexec-loaded kernel both "kexec -e" and "systemctl kexec" are equally valid.
* On comment 3 we proposed a script/approach to auto-test kexecs, used here to perform 1000 kexecs with the proposed patch.
[Regression Potential]
* Although the patch proposed here introduce a PCI handler, it kept the remove handler identical and based shutdown strongly on ena_remove(), changing just netdev handling following other upstream drivers. It was extensively tested and presented no issue. Also, it's self-contained and affect only one driver, so any other cloud providers or non-cloud environment wouldn't be even affected by the patch.
* In case of a potential regression, it could manifest as a delay or issue on reboot/shutdown path, only if ena driver is in use.
CVE References
Changed in linux (Ubuntu Eoan): | |
assignee: | nobody → Guilherme G. Piccoli (gpiccoli) |
Changed in linux (Ubuntu Bionic): | |
assignee: | nobody → Guilherme G. Piccoli (gpiccoli) |
Changed in linux (Ubuntu Xenial): | |
assignee: | nobody → Guilherme G. Piccoli (gpiccoli) |
Changed in linux (Ubuntu Eoan): | |
importance: | Undecided → High |
Changed in linux (Ubuntu Bionic): | |
importance: | Undecided → High |
Changed in linux (Ubuntu Xenial): | |
importance: | Undecided → High |
Changed in linux (Ubuntu Eoan): | |
status: | New → Confirmed |
Changed in linux (Ubuntu Bionic): | |
status: | New → Confirmed |
Changed in linux (Ubuntu Xenial): | |
status: | New → Confirmed |
description: | updated |
Changed in linux (Ubuntu Xenial): | |
status: | Confirmed → In Progress |
Changed in linux (Ubuntu Bionic): | |
status: | Confirmed → In Progress |
Changed in linux (Ubuntu Eoan): | |
status: | Confirmed → In Progress |
Changed in linux (Ubuntu Focal): | |
status: | Confirmed → In Progress |
Changed in linux (Ubuntu Disco): | |
status: | New → Fix Committed |
Changed in linux (Ubuntu Disco): | |
importance: | Undecided → Medium |
assignee: | nobody → Guilherme G. Piccoli (gpiccoli) |
Changed in linux (Ubuntu Focal): | |
status: | Fix Committed → Fix Released |
Changed in linux (Ubuntu Disco): | |
importance: | Medium → Low |
status: | Opinion → Won't Fix |
Changed in linux (Ubuntu): | |
status: | Fix Committed → Fix Released |
no longer affects: | linux (Ubuntu Disco) |
An initrd corruption in AWS Nitro (KVM-based) instances was reported when trying multiple kexecs sequentially - it usually manifests after the 2nd or 3rd kexec. By using pstore/ramoops, we collected the attached log.