Support for VMGenID device on x86 microVMs #4487

bchalios · 2024-03-06T10:07:06Z

Changes

Add support for Virtual Machine Generation ID for x86 microVMs. This also adds support for the ACPI Generic Event Device which routes interrupts for ACPI devices. VMGenID provides to the guest a 16-byte cryptographically random number which changes every time the microVM resumes from a snapshot.

Reason

VMGenID is used by the Linux kernel to re-seed its internal PRNG whenever a VM resumes from a snapshot. With Linux 6.8, Linux VMGenID driver will also emit a uevent to guest user-space every time the generation ID changes (i.e. the VM resumes from a snapshot).

License Acceptance

By submitting this pull request, I confirm that my contribution is made under
the terms of the Apache 2.0 license. For more information on following Developer
Certificate of Origin and signing off your commits, please check
CONTRIBUTING.md.

PR Checklist

If a specific issue led to this PR, this PR closes the issue.
The description of changes is clear and encompassing.
Any required documentation changes (code and docs) are included in this
PR.
API changes follow the Runbook for Firecracker API changes.
User-facing changes are mentioned in CHANGELOG.md.
All added/changed functionality is tested.
New TODOs link to an issue.
Commits meet
contribution quality standards.

This functionality cannot be added in rust-vmm.

bchalios · 2024-03-06T10:07:45Z

This is still a draft, since it depends on #4428

codecov · 2024-03-06T10:11:55Z

Codecov Report

Attention: Patch coverage is 95.69378% with 9 lines in your changes are missing coverage. Please review.

Project coverage is 82.14%. Comparing base (9f8b0b2) to head (90db35b).

Files	Patch %	Lines
src/vmm/src/devices/acpi/vmgenid.rs	94.04%	5 Missing ⚠️
src/vmm/src/device_manager/acpi.rs	96.66%	2 Missing ⚠️
src/vmm/src/device_manager/persist.rs	92.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4487      +/-   ##
==========================================
+ Coverage   82.04%   82.14%   +0.09%     
==========================================
  Files         253      255       +2     
  Lines       31072    31278     +206     
==========================================
+ Hits        25492    25692     +200     
- Misses       5580     5586       +6

Flag	Coverage Δ
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4.14-m6i.metal	`79.62% <95.69%> (+0.12%)`	⬆️
4.14-m7g.metal	`76.69% <100.00%> (?)`
5.10-c5n.metal	`82.15% <95.69%> (+0.10%)`	⬆️
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5.10-m7g.metal	`79.46% <100.00%> (?)`
6.1-c5n.metal	`82.15% <95.69%> (+0.11%)`	⬆️
6.1-m5n.metal	`82.14% <95.69%> (+0.11%)`	⬆️
6.1-m6a.metal	`81.44% <95.69%> (+0.11%)`	⬆️
6.1-m6g.metal	`79.46% <100.00%> (+<0.01%)`	⬆️
6.1-m6i.metal	`82.13% <95.69%> (+0.11%)`	⬆️
6.1-m7g.metal	`79.46% <100.00%> (?)`

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src/vmm/src/builder.rs

src/vmm/src/device_manager/acpi.rs

tests/integration_tests/security/test_vulnerabilities.py

docs/snapshotting/snapshot-support.md

docs/snapshotting/random-for-clones.md

wearyzen

still going through the code but here are some initial comments

CHANGELOG.md

docs/snapshotting/random-for-clones.md

docs/snapshotting/snapshot-support.md

bchalios · 2024-04-05T12:21:38Z

Changes from v1 to v2:

Fixed various references in the docs that VMGenID was added in Linux 6.1 (it was actually added in 5.18).
MMIODevManagerConstructorArgs now keeps a reference to guest memory, so we can avoid one clone() operation.
Removed comment that we need to inject the VMGenID notification after calling start_vcpus, as it was wrong.
Added explicit comment that VMGenID in kernels before 5.18 will have no effect in the guest.
dropped left over enable_console() call in tests.
Various typo fixes in documentation

src/vmm/src/devices/acpi/vmgenid.rs

src/vmm/src/device_manager/persist.rs

src/vmm/src/builder.rs

docs/snapshotting/snapshot-support.md

bchalios · 2024-04-05T15:34:58Z

Changes from v2 to v3:

Re-worked the logic to create VMGenID devices. Now, the resource allocation happens inside the VmGenId "constructor". Like that, we hide the logic of allocating resources which are specific to VMGenID devices.
Re-worked the logic for (de)serializing the VMGenID state, by moving VMGenID specific stuff under the VMGenID logic (similar to what we do with VirtIO devices).

ShadowCurse

Overall PR seems fine to me. The only thing to make it a bit better would be to split first commit into several commits smth like:

update mmio_restore_args
add acpi_device_manager
add vmgenid
...

src/vmm/src/lib.rs

tests/framework/artifacts.py

bchalios · 2024-04-08T11:50:51Z

@ShadowCurse regarding splitting the first commit in parts, I believe that splitting out the MMIO restore argument changes it makes sense. I don't see much value in splitting out the ACPI device manager though. Without the VMGenID changes, this would be just adding an empty struct (without any implementation at all). I would rather keep them together.

bchalios · 2024-04-08T12:21:34Z

Changes from v3 to v4:

Split out in its own commit the change that stores in MMIO constructor arguments a reference rather than the actual object.
Inlined one-liner function in tests that was only used in one place.
Bumped the snapshot version to 2.0.0 since VMGenID makes the snapshot format backwards incompatible with previous snapshots.

src/vmm/src/devices/acpi/vmgenid.rs

Use a reference to the GuestMemoryMmap rather than the object itself when restoring MMIO devices. This will avoid us a few clone() operations later on when we add support for restoring VMGenID, where we will need to pass information about the memory as well. Signed-off-by: Babis Chalios <bchalios@amazon.es>

Add support for the Virtual Machine Generation ID (VMGenID) device that allows notifying the guest about snapshot resume events. The device itself allocates one page of guest memory and an IRQ line. It stores a 16 bytes cryptographically random number (generation ID) at the beginning of this page. Once the microVM resumes from a snapshot, it writes a new 16-byte generation ID and sends an interrupt to the device. Also add support for the Generic Event Device, an ACPI device which handles IRQ lines allocated to ACPI devices and routes them as ACPI notifications to the devices the belong to. VMGenID state is saved in Firecracker snapshots. This renders the current snapshot format incompatible with all previous snapshot versions. Bump snapshot version to 2.0.0 to reflect that. Signed-off-by: Babis Chalios <bchalios@amazon.es>

We now reserve one IRQ for the VMGenID device, so we have one less IRQ available for VirtIO devices. Signed-off-by: Babis Chalios <bchalios@amazon.es>

tests/conftest.py

wearyzen

LGTM, I would however like to get a 2nd opinion on the kernels_unfiltered from @pb8o

At the moment, we filter out 6.1 guest kernel in all tests apart from PTP on Graviton. Add a new filter that allows select any kernel that exists in our CI artifacts folder and use it to create a pytest fixture for guest kernel 6.1, which works independently of the platform we run on. Signed-off-by: Babis Chalios <bchalios@amazon.es>

Add an integration test that launches a microVM, snapshots it repeatedly and checks for the existence of the message that the kernel emits every time it receives the VMGenID notification. Signed-off-by: Babis Chalios <bchalios@amazon.es>

In test_vulnerabilities.py we have various tests that check whether a condition holds after resuming from a snapshot. These checks seem to consistently fail if we take a snapshot before letting the guest kernel boot. Introduce an ssh command to ensure that the guest has booted before taking the snapshot so that we avoid the issue. Signed-off-by: Babis Chalios <bchalios@amazon.es>

Extend our current documentation for snapshotting and entropy recommendations with context about VMGenID. Mention the available VMGenID features depending on Linux version and also provide recommendations for entropy on VM clones based on VMGenID availability. Also, add CHANGELOG entry for VMGenID support. Signed-off-by: Babis Chalios <bchalios@amazon.es>

bchalios force-pushed the vmgenid_x86_64 branch 7 times, most recently from e488135 to 9f43105 Compare March 13, 2024 09:22

ShadowCurse mentioned this pull request Mar 16, 2024

[DRAFT] Prerequisite for proper device manager. #4509

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bchalios requested review from xmarcalx, kalyazin, pb8o and wearyzen as code owners April 4, 2024 16:08

bchalios self-assigned this Apr 4, 2024

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Refactoring of devices management #4542

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bchalios added 3 commits April 9, 2024 08:42

fix(test): set max device to 18 in test_max_devices

eaca56e

We now reserve one IRQ for the VMGenID device, so we have one less IRQ available for VirtIO devices. Signed-off-by: Babis Chalios <bchalios@amazon.es>

bchalios force-pushed the vmgenid_x86_64 branch from 594b4df to 3ad9a98 Compare April 9, 2024 08:43

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bchalios added 4 commits April 9, 2024 11:44

bchalios dismissed stale reviews from wearyzen and ShadowCurse via 9f28ece April 9, 2024 11:45

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Merge branch 'main' into vmgenid_x86_64

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bchalios merged commit 092d90a into firecracker-microvm:main Apr 9, 2024
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bchalios deleted the vmgenid_x86_64 branch April 9, 2024 15:31

bchalios mentioned this pull request May 13, 2024

[Snaps] #snapsafe support via VMGenID on ACPI #2476

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Support for VMGenID device on x86 microVMs #4487

Support for VMGenID device on x86 microVMs #4487

bchalios commented Mar 6, 2024 •

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Support for VMGenID device on x86 microVMs #4487

Support for VMGenID device on x86 microVMs #4487

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bchalios commented Mar 6, 2024 • edited Loading

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