Kyverno和SLSA 3

CNCF

发布于 2023-02-12 17:13:43

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发布于 2023-02-12 17:13:43

文章被收录于专栏：CNCF

Kyverno 项目如何符合 SLSA 第 3 级要求。

随着 Kyverno 1.9 的发布，Kyverno 开始了基于SLSA[1]标准生成和证明其发布工件的来源，并相信满足了第 3 级。这篇博客文章试图解释一点关于 SLSA 和第 3 级，以及我们如何满足要求。一旦OpenSSF[2]（Open Source Security Foundation，开源安全基金会）建立了它的一致性计划，我们希望看到这个过程得到官方的认可。

关于 SLSA

SLSA（发音：“salsa”，Supply chain Levels for Software Artifacts，软件工件的供应链级别），是一个安全框架，旨在防止篡改和保护项目中的工件。SLSA 有助于缓解供应链威胁。SLSA 合规性基于 4 个级别。第 1 级从基本要求开始，达到第 4 级需要严格加固供应链平台。

下图描述了几个已知的攻击点。有关详细的文档，请参考https://slsa.dev。

SLSA 要求和 Kyverno 合规状态

SLSA 将需求分为 3 个主要方面：源代码、构建和完整性。每个领域都有满足特定级别的子要求。由于 Kyverno 声称达到 SLSA 第 3 级，这份文件将解释我们是如何实现的。有关 SLSA 要求的完整摘要，请参考https://slsa.dev/spec/v0.1/requirements。

Source Requirements

Requirement	Required at SLSA Level 3	Met by Kyverno
Version controlled	Yes	Yes
Verified history	Yes	Yes
Retained indefinitely	Yes (for 18 months or above)	Yes

Version Controlled

Description:The source code should be tracked in a version-controlled system. The version control system should maintain the history of changes. The identification of uploaders and reviewers (if any), timestamps of the reviews, its content, and the parent reviews. Each revision should be tracked back using an immutable reference. These requirements are met by most of the revision systems, e.g git.

Kyverno Processes:Kyverno uses GitHub for source code management. Each commit gives info about the author, an explanation about the commit, and the time at which the commit was generated.

Verified History

Description:The history of a revision must be trackable. It should contain a timestamp and a strongly authenticated user (author, uploader, reviewer, etc.). The identities must use two-step verification or similar.

Kyverno Processes:Each commit in Kyverno contains a timestamp and info about the author. It also gives an explanation about the commit.

Retained Indefinitely

Description:If there are no legal or policy requirements, the revision and its change history must be preserved indefinitely and cannot be deleted. For SLSA Level 3, the retention can be limited to 18 months.

Kyverno Processes:The git tree remains unaltered. The source code of the build is archived.

Build Requirements

The conversion of source code into the build is the responsibility of the build system. The build system must be secured against any sort of outside intervention. The build system should produce the builds in a reproducible manner for verification.

Requirement	Required at SLSA Level 3	Met by Kyverno
Scripted build	Yes	Yes
Build service	Yes	Yes
Build as code	Yes	Yes
Ephemeral environment	Yes	Yes
Isolated	Yes	Yes

Scripted Build

Description:All build steps should be defined in the build script. e.g Makefile or GitHub action workflow file. The invocation command for build script is the only manual command allowed.

Kyverno Processes:Since the Kyverno code base is stored in GitHub, GitHub Actions are used to invoke build scripts. Kyverno uses a mix of Makefile and GitHub Workflows. Everything is declared inside build scripts.

Build Service

Description:The build step should be executed on some build service environment e.g GitHub Action, AWS CodePipeline. The developer workstation doesn't qualify as a build service.

Kyverno Processes:As mentioned above, the Kyverno source code is stored in GitHub. Kyverno relies on GitHub Actions as a build service environment.

Build As Code

Description:The build definition and configuration used by the build service to generate the build must be derived from text files. The build-as-code files need to be stored in the version control system.

Kyverno Processes:The build is generated by executing GitHub workflows. The build definition and configuration are all defined in workflow files under the directory .github/workflows/ in the kyverno/kyverno repository[3].

Ephemeral Environment

Description:The build step should be executed in an ephemeral environment. The environment should be solely created for this build and must not be reused. e.g container or VM.

Kyverno Processes:Kyverno relies on GitHub Actions as a build service environment. GitHub uses the concept of runners and the Kyverno project uses GitHub-hosted runners[4]. For each job, a new virtual machine is created.

Isolated

Description:The build step should be executed independently of each other. The build instance, either prior or concurrent, should not influence others.

Kyverno Processes:The GitHub-hosted runners run each job in a separate virtual machine. When the job has finished, the VM is automatically decommissioned.

Provenance Requirements

In order to prove that build was produced and artifacts were produced according to SLSA Level 3, SLSA mentions some requirements for provenance which can be grouped into the following:

Requirements on the process by which provenance is generated and consumed
Requirements on the content of the provenance

Kyverno relies on the official SLSA GitHub Generator project[5] for provenance generation. For more information on the generator project, see https://github.com/slsa-framework/slsa-github-generator.

Requirements on the process by which provenance is generated and consumed

Requirement	Required at SLSA Level 3	Met by Kyverno
Available	Yes	Yes
Authenticated	Yes	Yes
Service generated	Yes	Yes
Non-falsifiable	Yes	Yes

Available

Description:The provenance should be provided to the customer in a format accepted by the customer.

Kyverno Processes:Kyverno relies on the official SLSA GitHub generator framework[6] to provide provenance in the in-toto[7] format. The provenance is attested using the Sigstore[8] cosign[9] project and is publicly available as an image artifact on GitHub Container Registry stored in the same repository as the Kyverno container images themselves. This repository and its contents can be publicly pulled without authentication.

Authenticated

Description:The consumer can verify the authenticity and integrity of the provenance.

Kyverno Processes:The provenance is signed by OIDC identity and the public key to verify the provenance is stored in the public Rekor transparency log[10]. If someone tampers with the file then the signature will fail to verify. Anyone can verify the provenance for Kyverno artifacts with the process documented here[11].

Service Generated

Description:The provenance data should be obtained from the build service.

Kyverno Processes:The GitHub Action reusable workflow hosted by the SLSA GitHub Generator project creates the provenance file. The caller workflow from the Kyverno project is release.yaml and the called workflow is generator_container_slsa3.yml. The necessary data to the called workflow is passed in the form of variables and secrets. The called workflow is a third-party workflow which is used by Kyverno for provenance generation and any actions in the called workflow run as if they were part of the caller workflow.

Non-Falsifiable

Description:The build service's users can not falsify the provenance.

Kyverno Processes:GitHub takes care of avoiding interference with the build system. GitHub uses ephemeral and isolated virtual machines, no one can persistently compromise this environment. GitHub automatically provisions a new VM for that job. When the job execution is finished, the VM is automatically decommissioned. Use of the SLSA GitHub generator[12] separates the signing from building so the Kyverno build itself never has access to the signing secrets. Use of OIDC-based secrets through Sigstore's keyless signing[13] means the ephemeral signing secret is associated only with one specific build making it easy to detect secret theft and an attempt at signing something else.

Provenance Content Requirements

Requirement	Required at SLSA Level 3	Met by Kyverno
Identifies artifact	Yes	Yes
Identifies builder	Yes	Yes
Identifies build instructions	Yes	Yes
Identifies source code	Yes	Yes
Identifies entry point	Yes	Yes
Includes all build parameters	Yes	Yes

Identifies Artifact

Description:The output artifact must be identified by provenance by at least one cryptographic hash.

Kyverno Processes:The provenance file stores SHA-256 hashes of build artifacts. The provenance identifies the container image using its digest in SHA-256 format.

Identifies Builder

Description:The entity who executed the build process and generated the provenance should be identified by provenance.

Kyverno Processes:The id of the builder is added to provenance in the predicate.builder section. In case of Kyverno, GitHub Actions act as the builder. The build logic is defined inside GitHub workflows file. The provenance generation logic is in a separate reusable workflow which is recorded in the predicate.builder section. As an example, refer to the Provenance Example section.

Identifies Build Instructions

Description:The top-level instruction that was executed to initiate the build should be available in the provenance file.

Kyverno Processes:The top-level instruction is the GitHub Action workflow which is calling the provenance generation workflow. This is recorded in invocation.entrypoint in the provenance file. In Kyverno's case, it is release.yaml. The SLSA requirements mentions that "The identified instructions should be at the highest level available to the build" so it doesn't necessarily need to record all the the instructions as they are part of workflow file. As an example, refer to the Provenance Example section.

Identifies Source Code

Description:The repository origin of the source code used in the build must be identified in provenance.

Kyverno Processes:The repository information is stored in the provenance file. This is recorded in the predicate.invocation section. As an example, refer to the Provenance Example section.

Identifies Entry Point

Description:The processes which started the build processes should be identified by provenance.

Kyverno Processes:The required information is stored in the invocation.configSource.entryPoint in the provenance file. As an example, refer to the Provenance Example section.

Include All Build Parameters

Description:The provenance must include all the build parameters which are under user control.

Kyverno Processes:The main GitHub Action workflow file does not accept any parameters. The workflow_dispatch section in the release.yaml file does not accept any parameters. At SLSA level 3 the parameters, if any, must be listed. At SLSA level 4, the parameters must be empty.

Provenance Example

The following is an example of the generated provenance for Kyverno which will be returned from the process documented here[14].

{
  "_type": "https://in-toto.io/Statement/v0.1",
  "predicateType": "https://slsa.dev/provenance/v0.2",
  "subject": [
    {
      "name": "ghcr.io/kyverno/kyverno",
      "digest": {
        "sha256": "96a54a5747485b800adf05ff84d48fc9a8b66f1cdf9087cbed385dacc1cdb4d6"
      }
    }
  ],
  "predicate": {
    "builder": {
      "id": "https://github.com/slsa-framework/slsa-github-generator/.github/workflows/generator_container_slsa3.yml@refs/tags/v1.4.0"
    },
    "buildType": "https://github.com/slsa-framework/slsa-github-generator/container@v1",
    "invocation": {
      "configSource": {
        "uri": "git+https://github.com/kyverno/kyverno@refs/tags/v1.9.0-beta.2",
        "digest": {
          "sha1": "ab368ebc080535448aa08fafdff82a4d4c69e127"
        },
        "entryPoint": ".github/workflows/release.yaml"
      },
      "parameters": {},
      "environment": {
        "github_actor": "realshuting",
        "github_actor_id": "25727662",
        "github_base_ref": "",
        "github_event_name": "push",
        "github_event_payload": {
          "after": "9d6e981a64b0b8dc357befb7fc811304d7b11f7b",
          "base_ref": null,
          "before": "0000000000000000000000000000000000000000",
          "commits": [],
          "compare": "https://github.com/kyverno/kyverno/compare/v1.9.0-beta.2",
          "created": true,
          "deleted": false,
          "enterprise": {
            "avatar_url": "https://avatars.githubusercontent.com/b/9995?v=4",
            "created_at": "2021-11-03T14:57:36Z",
            "description": "",
            "html_url": "https://github.com/enterprises/cncf",
            "id": 9995,
            "name": "Cloud Native Computing Foundation",
            "node_id": "E_kgDNJws",
            "slug": "cncf",
            "updated_at": "2022-12-27T16:04:12Z",
            "website_url": "https://cncf.io"
          },
          "forced": false,
          "head_commit": {
            "author": {
              "email": "shuting@nirmata.com",
              "name": "shuting",
              "username": "realshuting"
            },
            "committer": {
              "email": "noreply@github.com",
              "name": "GitHub",
              "username": "web-flow"
            },
            "distinct": true,
            "id": "ab368ebc080535448aa08fafdff82a4d4c69e127",
            "message": "tag v1.9.0-beta.2 (#5959)",
            "timestamp": "2023-01-10T11:45:52Z",
            "tree_id": "95c14e810108e4125c571ba33483204f4b078900",
            "url": "https://github.com/kyverno/kyverno/commit/ab368ebc080535448aa08fafdff82a4d4c69e127"
          },
          "organization": {
            "avatar_url": "https://avatars.githubusercontent.com/u/68448710?v=4",
            "description": "Kubernetes Native Policy Management",
            "events_url": "https://api.github.com/orgs/kyverno/events",
            "hooks_url": "https://api.github.com/orgs/kyverno/hooks",
            "id": 68448710,
            "issues_url": "https://api.github.com/orgs/kyverno/issues",
            "login": "kyverno",
            "members_url": "https://api.github.com/orgs/kyverno/members{/member}",
            "node_id": "MDEyOk9yZ2FuaXphdGlvbjY4NDQ4NzEw",
            "public_members_url": "https://api.github.com/orgs/kyverno/public_members{/member}",
            "repos_url": "https://api.github.com/orgs/kyverno/repos",
            "url": "https://api.github.com/orgs/kyverno"
          },
          "pusher": {
            "email": "shutting06@gmail.com",
            "name": "realshuting"
          },
          "ref": "refs/tags/v1.9.0-beta.2",
          "repository": {
            "allow_forking": true,
            "archive_url": "https://api.github.com/repos/kyverno/kyverno/{archive_format}{/ref}",
            "archived": false,
            "assignees_url": "https://api.github.com/repos/kyverno/kyverno/assignees{/user}",
            "blobs_url": "https://api.github.com/repos/kyverno/kyverno/git/blobs{/sha}",
            "branches_url": "https://api.github.com/repos/kyverno/kyverno/branches{/branch}",
            "clone_url": "https://github.com/kyverno/kyverno.git",
            "collaborators_url": "https://api.github.com/repos/kyverno/kyverno/collaborators{/collaborator}",
            "comments_url": "https://api.github.com/repos/kyverno/kyverno/comments{/number}",
            "commits_url": "https://api.github.com/repos/kyverno/kyverno/commits{/sha}",
            "compare_url": "https://api.github.com/repos/kyverno/kyverno/compare/{base}...{head}",
            "contents_url": "https://api.github.com/repos/kyverno/kyverno/contents/{+path}",
            "contributors_url": "https://api.github.com/repos/kyverno/kyverno/contributors",
            "created_at": 1549297548,
            "default_branch": "main",
            "deployments_url": "https://api.github.com/repos/kyverno/kyverno/deployments",
            "description": "Kubernetes Native Policy Management",
            "disabled": false,
            "downloads_url": "https://api.github.com/repos/kyverno/kyverno/downloads",
            "events_url": "https://api.github.com/repos/kyverno/kyverno/events",
            "fork": false,
            "forks": 479,
            "forks_count": 479,
            "forks_url": "https://api.github.com/repos/kyverno/kyverno/forks",
            "full_name": "kyverno/kyverno",
            "git_commits_url": "https://api.github.com/repos/kyverno/kyverno/git/commits{/sha}",
            "git_refs_url": "https://api.github.com/repos/kyverno/kyverno/git/refs{/sha}",
            "git_tags_url": "https://api.github.com/repos/kyverno/kyverno/git/tags{/sha}",
            "git_url": "git://github.com/kyverno/kyverno.git",
            "has_discussions": true,
            "has_downloads": true,
            "has_issues": true,
            "has_pages": true,
            "has_projects": true,
            "has_wiki": true,
            "homepage": "https://kyverno.io",
            "hooks_url": "https://api.github.com/repos/kyverno/kyverno/hooks",
            "html_url": "https://github.com/kyverno/kyverno",
            "id": 169108858,
            "is_template": false,
            "issue_comment_url": "https://api.github.com/repos/kyverno/kyverno/issues/comments{/number}",
            "issue_events_url": "https://api.github.com/repos/kyverno/kyverno/issues/events{/number}",
            "issues_url": "https://api.github.com/repos/kyverno/kyverno/issues{/number}",
            "keys_url": "https://api.github.com/repos/kyverno/kyverno/keys{/key_id}",
            "labels_url": "https://api.github.com/repos/kyverno/kyverno/labels{/name}",
            "language": "Go",
            "languages_url": "https://api.github.com/repos/kyverno/kyverno/languages",
            "license": {
              "key": "apache-2.0",
              "name": "Apache License 2.0",
              "node_id": "MDc6TGljZW5zZTI=",
              "spdx_id": "Apache-2.0",
              "url": "https://api.github.com/licenses/apache-2.0"
            },
            "master_branch": "main",
            "merges_url": "https://api.github.com/repos/kyverno/kyverno/merges",
            "milestones_url": "https://api.github.com/repos/kyverno/kyverno/milestones{/number}",
            "mirror_url": null,
            "name": "kyverno",
            "node_id": "MDEwOlJlcG9zaXRvcnkxNjkxMDg4NTg=",
            "notifications_url": "https://api.github.com/repos/kyverno/kyverno/notifications{?since,all,participating}",
            "open_issues": 296,
            "open_issues_count": 296,
            "organization": "kyverno",
            "owner": {
              "avatar_url": "https://avatars.githubusercontent.com/u/68448710?v=4",
              "email": "kyverno@googlegroups.com",
              "events_url": "https://api.github.com/users/kyverno/events{/privacy}",
              "followers_url": "https://api.github.com/users/kyverno/followers",
              "following_url": "https://api.github.com/users/kyverno/following{/other_user}",
              "gists_url": "https://api.github.com/users/kyverno/gists{/gist_id}",
              "gravatar_id": "",
              "html_url": "https://github.com/kyverno",
              "id": 68448710,
              "login": "kyverno",
              "name": "kyverno",
              "node_id": "MDEyOk9yZ2FuaXphdGlvbjY4NDQ4NzEw",
              "organizations_url": "https://api.github.com/users/kyverno/orgs",
              "received_events_url": "https://api.github.com/users/kyverno/received_events",
              "repos_url": "https://api.github.com/users/kyverno/repos",
              "site_admin": false,
              "starred_url": "https://api.github.com/users/kyverno/starred{/owner}{/repo}",
              "subscriptions_url": "https://api.github.com/users/kyverno/subscriptions",
              "type": "Organization",
              "url": "https://api.github.com/users/kyverno"
            },
            "private": false,
            "pulls_url": "https://api.github.com/repos/kyverno/kyverno/pulls{/number}",
            "pushed_at": 1673351226,
            "releases_url": "https://api.github.com/repos/kyverno/kyverno/releases{/id}",
            "size": 75072,
            "ssh_url": "git@github.com:kyverno/kyverno.git",
            "stargazers": 3340,
            "stargazers_count": 3340,
            "stargazers_url": "https://api.github.com/repos/kyverno/kyverno/stargazers",
            "statuses_url": "https://api.github.com/repos/kyverno/kyverno/statuses/{sha}",
            "subscribers_url": "https://api.github.com/repos/kyverno/kyverno/subscribers",
            "subscription_url": "https://api.github.com/repos/kyverno/kyverno/subscription",
            "svn_url": "https://github.com/kyverno/kyverno",
            "tags_url": "https://api.github.com/repos/kyverno/kyverno/tags",
            "teams_url": "https://api.github.com/repos/kyverno/kyverno/teams",
            "topics": [
              "kubernetes",
              "policy-management"
            ],
            "trees_url": "https://api.github.com/repos/kyverno/kyverno/git/trees{/sha}",
            "updated_at": "2023-01-10T06:16:33Z",
            "url": "https://github.com/kyverno/kyverno",
            "visibility": "public",
            "watchers": 3340,
            "watchers_count": 3340,
            "web_commit_signoff_required": true
          },
          "sender": {
            "avatar_url": "https://avatars.githubusercontent.com/u/25727662?v=4",
            "events_url": "https://api.github.com/users/realshuting/events{/privacy}",
            "followers_url": "https://api.github.com/users/realshuting/followers",
            "following_url": "https://api.github.com/users/realshuting/following{/other_user}",
            "gists_url": "https://api.github.com/users/realshuting/gists{/gist_id}",
            "gravatar_id": "",
            "html_url": "https://github.com/realshuting",
            "id": 25727662,
            "login": "realshuting",
            "node_id": "MDQ6VXNlcjI1NzI3NjYy",
            "organizations_url": "https://api.github.com/users/realshuting/orgs",
            "received_events_url": "https://api.github.com/users/realshuting/received_events",
            "repos_url": "https://api.github.com/users/realshuting/repos",
            "site_admin": false,
            "starred_url": "https://api.github.com/users/realshuting/starred{/owner}{/repo}",
            "subscriptions_url": "https://api.github.com/users/realshuting/subscriptions",
            "type": "User",
            "url": "https://api.github.com/users/realshuting"
          }
        },
        "github_head_ref": "",
        "github_ref": "refs/tags/v1.9.0-beta.2",
        "github_ref_type": "tag",
        "github_repository_id": "169108858",
        "github_repository_owner": "kyverno",
        "github_repository_owner_id": "68448710",
        "github_run_attempt": "1",
        "github_run_id": "3883016519",
        "github_run_number": "232",
        "github_sha1": "ab368ebc080535448aa08fafdff82a4d4c69e127"
      }
    },
    "metadata": {
      "buildInvocationID": "3883016519-1",
      "completeness": {
        "parameters": true,
        "environment": false,
        "materials": false
      },
      "reproducible": false
    },
    "materials": [
      {
        "uri": "git+https://github.com/kyverno/kyverno@refs/tags/v1.9.0-beta.2",
        "digest": {
          "sha1": "ab368ebc080535448aa08fafdff82a4d4c69e127"
        }
      }
    ]
  }
}

总结

SLSA 项目在确保软件供应链的完整性方面提供了巨大的收益。

参考资料

[1]

SLSA: https://slsa.dev/

[2]

OpenSSF: https://openssf.org/

[3]

kyverno/kyverno repository: https://github.com/kyverno/kyverno

[4]

GitHub-hosted runners: https://docs.github.com/en/actions/using-github-hosted-runners/about-github-hosted-runners

[5]

SLSA GitHub Generator project: https://github.com/slsa-framework/slsa-github-generator

[6]

SLSA GitHub generator framework: https://github.com/slsa-framework/slsa-github-generator

[7]

in-toto: https://in-toto.io/

[8]

Sigstore: https://www.sigstore.dev/

[9]

cosign: https://github.com/sigstore/cosign

[10]

Rekor transparency log: https://docs.sigstore.dev/rekor/overview/

[11]

here: https://kyverno.io/docs/security/#verifying-provenance

[12]

SLSA GitHub generator: https://github.com/slsa-framework/slsa-github-generator

[13]

keyless signing: https://github.com/sigstore/cosign/blob/main/KEYLESS.md

[14]

here: https://kyverno.io/docs/security/#verifying-provenance

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