OpenSSL static linking proposal

[qmuntal]

Goal

Add OpenSSL static linking support to Microsoft Go OpenSSL crypto backend.

Background

We currently support OpenSSL dynamic loading by calling dlopen(libcrypto.so.X), being X a configurable version string (see docs). The supported OpenSSL versions are 1.0.2, 1.1.0, 1.1.1 and 3.

We also support portable OpenSSL, which means users can build an application using an OpenSSL version different that the one used at runtime.

One can tune the FIPS behavior by using the GOFIPS environment variable in the following ways:

• GOFIPS=0: disable OpenSSL FIPS mode.
• GOFIPS=1: force OpenSSL FIPS mode, panic is not enabled and can't be enabled.
• GOFIPS unset: try to enable FIPS mode if not enabled. If can't be enabled, go on with the OpenSSL backend in non-FIPS mode.

OpenSSL static linking is not supported, although we could add this capability to go-crypto-openssl with a reasonable effort. This proposal is not about how to update go-crypto-openssl nor how is integrated with microsoft/go, but about the user experience around the different OpenSSL linking/loading modes

Why static linking

• Deploy on distroless containers: some containers are so trimmed down that they don't even contain libcrypto.so, so embedding it into the binary facilitate running it without installing external packages.
• Ensure OpenSSL is FIPS-compliant: we currently require the platform OpenSSL to be FIPS-compliant, which is not the case for popular containers, such as Ubuntu. CBL-Mariner does provide a FIPS-compliant OpenSSL out of the box.

Proposal

• GOEXPERIMENT=opensslcrypto uses dynamic loading (aka dlopen) by default, which is the current behavior. Using the platform crypto is the Microsoft Crypto Board recommendation, so we should stick to it.
• GOEXPERIMENT=opensslcrypto uses static linking when used together with -tags=opensslstatic.
  e.g., GOEXPERIMENT=opensslcrypto go build . -tags=opensslstatic.
• Microsoft Go will provide the OpenSSL library that will be used for static linking, in a similar way as Google does for BoringSSL. This library will be FIPS-capable and vetted by Microsoft's Crypto Board. The Microsoft Go team shouldn't be responsible of maintaining this library, it should either build the source code from a trusted repository (e.g. CBL-Mariner) using a compliant build recipe or just take the pre-compiled binaries.
• Microsoft Go won't provide multiple OpenSSL versions. This should be transparent for end users as long as OpenSSL integrates well with Go crypto.
• Microsoft Go won't support linking against custom OpenSSL static libraries. The business case of this functionality is not clear and would complicate the implementation. This decision can be revisit later on.
• Change GOFIPS to default to `GOFIPS=1, which means it will panic if OpenSSL cannot be used in FIPS mode. If someone is not sure whether FIPS mode will be supported at runtime they should use OpenSSL static linking, which will be warranted to support FIPS.

The most difficult part of this proposal is to agree on who provides the FIPS-capable OpenSSL sources and built recipe. This proposal is consciously vague at this point so we focus the discussion on the UX. If at the end we can't provide a FIPS-capable OpenSSL static library I would argue that we should not provide OpenSSL static linking at all.

@dagood @jaredpar @chsienki
FYI @derekparker

[derekparker]

cc @simo5 @ueno

[dagood]

• The Microsoft Go team shouldn't be responsible of maintaining this library, it should build the source code from a trusted repository (e.g. CBL-Mariner) using a compliant build recipe.

Do we (microsoft/go) need to build this from source to satisfy some UX? I think we should be open to acquiring the actual binaries from CBL-Mariner, so they keep control over the entire build process. We already build our Linux platform Go on a Mariner container, so we already have these binaries on the build machine.

This also is what Mariner would need to do when they build Microsoft Go from source, so if we can both use the same binary ingestion process, I think that will work well for everyone.

This isn't the focus of the proposal and you mentioned keeping this part vague, I think it's probably just not quite vague enough. 😄

[qmuntal]

Do we (microsoft/go) need to build this from source to satisfy some UX? I think we should be open to acquiring the actual binaries from CBL-Mariner, so they keep control over the entire build process. We already build our Linux platform Go on a Mariner container, so we already have these binaries on the build machine.

This is a possibility and could be a good initial plan. What worries me is that Mariner only provides amd64 binaries, thus it wouldn't work for arm64. I'm not aware of any requirement to support arm64, but something to keep in mind.

[dagood]

What worries me is that Mariner only provides amd64 binaries

They have arm64 too, just not armv6l. From emulated Docker:

root [ / ]# rpm -q --whatprovides /usr/lib/libcrypto.so.1.1.1k
openssl-libs-1.1.1k-12.cm1.aarch64
root [ / ]# file /usr/lib/libcrypto.so.1.1.1k
/usr/lib/libcrypto.so.1.1.1k: ELF 64-bit LSB shared object, ARM aarch64, version 1 (SYSV), statically linked, BuildID[sha1]=dfa8ebe52a3de49330d9867765450d98db00d73d, with debug_info, not stripped, too many notes (256)

[qmuntal]

What worries me is that Mariner only provides amd64 binaries

They have arm64 too, just not armv6l. From emulated Docker:

root [ / ]# rpm -q --whatprovides /usr/lib/libcrypto.so.1.1.1k
openssl-libs-1.1.1k-12.cm1.aarch64
root [ / ]# file /usr/lib/libcrypto.so.1.1.1k
/usr/lib/libcrypto.so.1.1.1k: ELF 64-bit LSB shared object, ARM aarch64, version 1 (SYSV), statically linked, BuildID[sha1]=dfa8ebe52a3de49330d9867765450d98db00d73d, with debug_info, not stripped, too many notes (256)

You got me there. I'll update the proposal to include this option 😄

[qmuntal]

OpenSSL 3 dynamically loads providers, so it is not possible to achieve self-contained binaries when using OpenSSL. Also, it is not recommended to statically link libraries that use dynamic loading due to glibc compatibility issues. I'm retracting this proposal given these facts.