mirror of
https://github.com/edgelesssys/constellation.git
synced 2024-12-25 23:49:37 -05:00
89 lines
3.9 KiB
Markdown
89 lines
3.9 KiB
Markdown
# PCR-updater
|
|
|
|
New images result in different PCR values for the image.
|
|
This utility program makes it simple to update the expected PCR values of the CLI.
|
|
|
|
## Usage
|
|
|
|
To read the PCR state of any running Constellation node, run the following:
|
|
|
|
```shell
|
|
go run main.go -constell-ip <NODE_IP> -constell-port <VERIFY_SERVICE_PORT>
|
|
```
|
|
|
|
The output is similar to the following:
|
|
|
|
```shell
|
|
$ go run main.go -constell-ip 192.0.2.3 -constell-port 30081
|
|
connecting to verification service at 192.0.2.3:30081
|
|
PCRs:
|
|
{
|
|
"0": "DzXCFGCNk8em5ornNZtKi+Wg6Z7qkQfs5CfE3qTkOc8=",
|
|
"1": "XBoRlWuQx6nIDr5vgUL0DlJHy6H6u1dPU3qK2NyToc8=",
|
|
"10": "WLmYFRmDft/ajZJ056CAhpheU6Vbt73aR8eIQpLRGq0=",
|
|
"11": "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=",
|
|
"12": "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=",
|
|
"13": "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=",
|
|
"14": "4tPyJd6A5g09KduV3+nWZQCiEzHAiRT5DulmAqlvpZU=",
|
|
"15": "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=",
|
|
"16": "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=",
|
|
"17": "//////////////////////////////////////////8=",
|
|
"18": "//////////////////////////////////////////8=",
|
|
"19": "//////////////////////////////////////////8=",
|
|
"2": "PUWM/lXMA+ofRD8VYr7sjfUcdeFKn8+acjShPxmOeWk=",
|
|
"20": "//////////////////////////////////////////8=",
|
|
"21": "//////////////////////////////////////////8=",
|
|
"22": "//////////////////////////////////////////8=",
|
|
"23": "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=",
|
|
"3": "PUWM/lXMA+ofRD8VYr7sjfUcdeFKn8+acjShPxmOeWk=",
|
|
"4": "MmkueFj1rP2seH+bjeIRsO4dUnLnMdl7QgtGoAtQH7M=",
|
|
"5": "ExaiapuIfo0KMBo8wj6kPDORLocgnH1C0G/KY8DcV3A=",
|
|
"6": "PUWM/lXMA+ofRD8VYr7sjfUcdeFKn8+acjShPxmOeWk=",
|
|
"7": "UZcW+fhFRMpFkgU+EfKG2s3KdmgEA+TD2quLmthQHbo=",
|
|
"8": "KLSMootYaHBjysWKq9CAYXkXpeYx9PUBimlSEZGJqUM=",
|
|
"9": "gse53SjsqREEdOpImJH4KAb0b8PqIgwI+Ps/XSiFnN4="
|
|
}
|
|
```
|
|
|
|
### Extend Config
|
|
|
|
To set measurement values in Constellation config, use `yaml` format option.
|
|
Optionally filter down results measurements per cloud provider:
|
|
|
|
Azure
|
|
|
|
```bash
|
|
./pcr-reader --constell-ip ${CONSTELLATION_IP} --format yaml | yq e 'del(.[0,6,10,11,12,13,14,15,16,17,18,19,20,21,22,23])' -
|
|
```
|
|
|
|
## Meaning of PCR values
|
|
|
|
An overview about what data is measured into the different registers can be found [in the TPM spec](https://trustedcomputinggroup.org/wp-content/uploads/TCG_PCClient_PFP_r1p05_v23_pub.pdf#%5B%7B%22num%22%3A157%2C%22gen%22%3A0%7D%2C%7B%22name%22%3A%22XYZ%22%7D%2C33%2C400%2C0%5D).
|
|
|
|
We use the TPM and its PCRs to verify all nodes of a Constellation run with the same firmware and OS software.
|
|
|
|
### Azure trusted launch
|
|
|
|
PCR[0] measures the firmware volume (FV). Changes to FV also change PCR[0], making it unreliable for attestation.
|
|
PCR[6] measures the VM ID. This is unusable for cluster attestation for two reasons:
|
|
|
|
1. The verification service does not know the VM ID of nodes wanting to join the cluster, so it can not compute the expected PCR[6] for the joining VM
|
|
2. A user may attest any node of the cluster without knowing the VM ID
|
|
|
|
PCR[10] is used by Linux Integrity Measurement Architecture (IMA).
|
|
IMA creates runtime measurements based on a measurement policy (which is obsolete for Constellation, since we use dm-verity).
|
|
The first entry of the runtime measurements is the `boot_aggregate`. It is a SHA1 hash over PCRs 0 to 7.
|
|
As detailed earlier, PCR[6] is different for every VM in Azure, therefore PCR[10] will also be different since it includes PCR[6], meaning we can not use it for attestation.
|
|
IMA writing its measurements into PCR[10] can not be disabled without rebuilding the kernel.
|
|
|
|
### Azure flexible deployment and attestation (FDA)
|
|
|
|
With FDA CVMs measuring all of the firmware, it should be possible to use all PCRs for attestation since we know, and can choose, what firmware is running.
|
|
|
|
### GCP confidential VM
|
|
|
|
GCP uses confidential VMs based on AMD SEV-ES with a vTPM interface.
|
|
|
|
PCR[0] contains the measurement of a string marking the VM as using ADM SEV-ES.
|
|
All firmware measurements seem to be constant.
|