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michelle-clayton-work merged 1 commit into from
Apr 23, 2026
+147 −22
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Address GOFIPS short-circuit bug #2244

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17 changes: 17 additions & 0 deletions eng/doc/fips/README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -146,10 +146,23 @@ The Microsoft build of Go detects your FIPS mode preference by evaluating this l
- If environment variable setting `GODEBUG=fips140=on` is found: Enabled ✅
- More specifically, if [`GODEBUG`](https://go.dev/doc/godebug) contains `fips140=on`.
- This is the recommended way to set your FIPS preference.
- `GODEBUG=fips140=only` and `GODEBUG=fips140=debug` also enable FIPS mode. See [Go Runtime FIPS mode](#go-runtime-fips-mode).
- If environment variable setting `GODEBUG=fips140=off` is found: Disabled ❌
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michelle-clayton-work marked this conversation as resolved.
- This explicitly disables FIPS mode and skips platform-specific FIPS
detection (e.g. the Linux kernel FIPS flag). This is the only supported
way to skip platform FIPS detection.
- If the environment variable `GOFIPS` is set to:
- `1`: Enabled ✅
- Any other value (including `0` and the empty string) is ignored, and
detection continues with the next item in this list. To explicitly
disable FIPS mode and skip platform FIPS detection, use
`GODEBUG=fips140=off`.
- If the environment variable `GOLANG_FIPS` is set to:
- `1`: Enabled ✅
- Any other value (including `0` and the empty string) is ignored, and
detection continues with the next item in this list. To explicitly
disable FIPS mode and skip platform FIPS detection, use
`GODEBUG=fips140=off`.
- If a platform-specific preference is detected: Enabled ✅
- See the following sections for per-platform details.
- If the [build option to require FIPS mode](#build-option-to-require-fips-mode) is enabled: Enabled ✅
Expand Down Expand Up @@ -433,6 +446,9 @@ This list of major changes is intended for quick reference and for access to his
### Go 1.27 (Aug 2026)

- Support for `GODEBUG=fips140=only` has been added. It acts as `fips140=on`, but also panics if a non-FIPS-approved algorithm is used.
- `GODEBUG=fips140=off` now explicitly disables FIPS mode and skips the platform-specific FIPS detection (e.g. the Linux kernel FIPS flag at `/proc/sys/crypto/fips_enabled`). This is the supported way to opt out of platform FIPS detection. See [microsoft/go#2184](https://github.com/microsoft/go/issues/2184).
- `GOFIPS` now matches its documented behavior: only `GOFIPS=1` enables FIPS mode, and any other value (including `0` and the empty string) is treated as if `GOFIPS` were unset. The same applies to `GOLANG_FIPS`.
- In Go 1.25 and 1.26, due to a bug, setting `GOFIPS` (or `GOLANG_FIPS`) to any value silently bypassed the platform-specific FIPS detection (e.g. the Linux kernel FIPS flag) even though only `=1` actually enabled FIPS mode. Programs that previously relied on `GOFIPS=0` to skip platform FIPS detection should switch to `GODEBUG=fips140=off`.
- The per-platform GOEXPERIMENTs (`opensslcrypto`, `cngcrypto`, `darwincrypto`) have been removed.
- Using any of the removed experiments will result in a build error.
- The `systemcrypto` GOEXPERIMENT has been the preferred way to select a crypto backend since it was introduced in Go 1.21. It is now the only way.
Expand Down Expand Up @@ -463,6 +479,7 @@ This list of major changes is intended for quick reference and for access to his
- If your app doesn't use a crypto package and you make a change that introduces a crypto package dependency, you will only encounter a compatibility check failure after the change. The change may be in your transitive dependencies: for example, depending on a new module that uses `crypto/sha256` may trigger the compatibility check. This is undesirable, but it's necessary to enable flexibility.

- `GOFIPS=0` support has been removed. It now has no effect.
- Note: due to a bug, in Go 1.25 and 1.26 setting `GOFIPS` (or `GOLANG_FIPS`) to any value other than `1` actually still bypassed the platform-specific FIPS detection (e.g. the Linux kernel FIPS flag), even though it was documented as having no effect. This was fixed in Go 1.27, which also adds `GODEBUG=fips140=off` as the supported way to explicitly disable FIPS mode and skip platform FIPS detection. See [microsoft/go#2184](https://github.com/microsoft/go/issues/2184).

- `GOEXPERIMENT=boringcrypto` has been removed.

Expand Down
152 changes: 130 additions & 22 deletions patches/0003-Implement-crypto-internal-backend.patch
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Original file line number Diff line number Diff line change
Expand Up @@ -33,7 +33,8 @@ desired goexperiments and build tags.
src/crypto/internal/backend/bbig/big_linux.go | 12 +
.../internal/backend/bbig/big_windows.go | 12 +
src/crypto/internal/backend/common.go | 46 ++
.../internal/backend/fips140/fips140.go | 70 +++
.../internal/backend/fips140/fips140.go | 95 ++++
.../internal/backend/fips140/fips140_test.go | 75 +++
.../internal/backend/fips140/isrequirefips.go | 9 +
.../internal/backend/fips140/norequirefips.go | 9 +
.../backend/fips140/nosystemcrypto.go | 13 +
Expand All @@ -53,7 +54,7 @@ desired goexperiments and build tags.
src/go/build/deps_test.go | 24 +-
src/internal/buildcfg/exp.go | 47 ++
src/runtime/runtime_boring.go | 5 +
44 files changed, 2763 insertions(+), 16 deletions(-)
45 files changed, 2863 insertions(+), 16 deletions(-)
create mode 100644 src/cmd/go/systemcrypto_test.go
create mode 100644 src/crypto/internal/backend/backend_darwin.go
create mode 100644 src/crypto/internal/backend/backend_linux.go
Expand All @@ -65,6 +66,7 @@ desired goexperiments and build tags.
create mode 100644 src/crypto/internal/backend/bbig/big_windows.go
create mode 100644 src/crypto/internal/backend/common.go
create mode 100644 src/crypto/internal/backend/fips140/fips140.go
create mode 100644 src/crypto/internal/backend/fips140/fips140_test.go
create mode 100644 src/crypto/internal/backend/fips140/isrequirefips.go
create mode 100644 src/crypto/internal/backend/fips140/norequirefips.go
create mode 100644 src/crypto/internal/backend/fips140/nosystemcrypto.go
Expand Down Expand Up @@ -368,10 +370,10 @@ index a4edd854f1d35a..10ee92536b96cd 100644
// This will also update the BuildContext's tool tags to include the new
// experiment tags.
diff --git a/src/cmd/go/internal/load/pkg.go b/src/cmd/go/internal/load/pkg.go
index f40de7fe12fd37..04797bfc529ac1 100644
index 91282ef9ace1c6..8f0deba2378f44 100644
--- a/src/cmd/go/internal/load/pkg.go
+++ b/src/cmd/go/internal/load/pkg.go
@@ -2413,6 +2413,9 @@ func (p *Package) setBuildInfo(ctx context.Context, f *modfetch.Fetcher, autoVCS
@@ -2415,6 +2415,9 @@ func (p *Package) setBuildInfo(ctx context.Context, f *modfetch.Fetcher, autoVCS
buildmode = "archive"
}
}
Expand Down Expand Up @@ -2264,10 +2266,10 @@ index 00000000000000..a9682181ffa154
+}
diff --git a/src/crypto/internal/backend/fips140/fips140.go b/src/crypto/internal/backend/fips140/fips140.go
new file mode 100644
index 00000000000000..1bf7c3b7d63da8
index 00000000000000..6c3568d77d2c0a
--- /dev/null
+++ b/src/crypto/internal/backend/fips140/fips140.go
@@ -0,0 +1,70 @@
@@ -0,0 +1,95 @@
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
Expand Down Expand Up @@ -2297,20 +2299,7 @@ index 00000000000000..1bf7c3b7d63da8
+func init() {
+ // TODO: Decide which environment variable to use.
+ // See https://github.com/microsoft/go/issues/397.
+ var ok bool
+ value := fips140GODEBUG.Value()
+ if value == "on" || value == "only" || value == "debug" {
+ message = "environment variable GODEBUG=fips140=" + value
+ value = "1"
+ } else if value, ok = syscall.Getenv("GOFIPS"); ok {
+ message = "environment variable GOFIPS"
+ } else if value, ok = syscall.Getenv("GOLANG_FIPS"); ok {
+ message = "environment variable GOLANG_FIPS"
+ } else if systemFIPSMode() {
+ message = "system FIPS mode"
+ value = "1"
+ }
+ enabled = value == "1"
+ enabled, message = detect(fips140GODEBUG.Value(), syscall.Getenv, systemFIPSMode)
+ if isRequireFIPS {
+ if isSkipFIPSCheck {
+ panic("the 'requirefips' build tag is enabled, but it conflicts " +
Expand All @@ -2321,6 +2310,44 @@ index 00000000000000..1bf7c3b7d63da8
+ }
+}
+
+// detect reports whether FIPS 140 mode should be enabled and returns a
+// human-readable message describing how the decision was made.
+//
+// godebug is the value of the fips140 GODEBUG setting. getenv is used to look
+// up the GOFIPS and GOLANG_FIPS environment variables and mirrors the
+// semantics of [syscall.Getenv]. systemFIPS reports whether the platform
+// indicates that FIPS mode should be enabled (e.g. the Linux kernel FIPS flag).
+//
+// The inputs are taken as parameters, rather than read directly, to make the
+// detection logic easy to test without depending on process state.
+func detect(godebug string, getenv func(string) (string, bool), systemFIPS func() bool) (enabled bool, message string) {
+ switch godebug {
+ case "on", "only", "debug":
+ return true, "environment variable GODEBUG=fips140=" + godebug
+ case "off":
+ // GODEBUG=fips140=off explicitly disables FIPS mode and bypasses
+ // the platform-specific FIPS detection (e.g. the Linux kernel FIPS flag).
+ // This is the only supported way to skip the platform FIPS detection.
+ return false, "environment variable GODEBUG=fips140=off"
+ }
+ // Only "1" is a meaningful value for GOFIPS and GOLANG_FIPS. Any other
+ // value (including "0" and the empty string) is treated as if the
+ // variable were unset, to match the documented behavior and to avoid
+ // silently bypassing the platform FIPS detection due to a typo or
+ // accidental setting. To explicitly disable FIPS mode and skip the
+ // platform FIPS detection, use GODEBUG=fips140=off.
+ if v, ok := getenv("GOFIPS"); ok && v == "1" {
+ return true, "environment variable GOFIPS=1"
+ }
+ if v, ok := getenv("GOLANG_FIPS"); ok && v == "1" {
+ return true, "environment variable GOLANG_FIPS=1"
+ }
+ if systemFIPS() {
+ return true, "system FIPS mode"
+ }
+ return false, ""
+}
+
+// Check checks whether fips mode, as returned by fips(),
+// is valid given the current settings.
+func Check(fips func() bool) error {
Expand All @@ -2338,6 +2365,87 @@ index 00000000000000..1bf7c3b7d63da8
+ }
+ return nil
+}
diff --git a/src/crypto/internal/backend/fips140/fips140_test.go b/src/crypto/internal/backend/fips140/fips140_test.go
new file mode 100644
index 00000000000000..9fb7df809baed8
--- /dev/null
+++ b/src/crypto/internal/backend/fips140/fips140_test.go
@@ -0,0 +1,75 @@
+// Copyright 2026 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package fips140
+
+import (
+ "testing"
+)
+
+// fakeEnv returns a getenv function that serves lookups from m, with the
+// same (value, ok) semantics as [syscall.Getenv]. A key present in m with an
+// empty string value represents a set-but-empty environment variable.
+func fakeEnv(m map[string]string) func(string) (string, bool) {
+ return func(key string) (string, bool) {
+ v, ok := m[key]
+ return v, ok
+ }
+}
+
+// TestDetect exercises the FIPS 140 detection logic in isolation, without
+// depending on process environment variables or the host's kernel FIPS
+// configuration. This lets us cover combinations that would otherwise be
+// impossible to test on a single machine, such as the kernel FIPS flag
+// being set or not set for the same test run.
+func TestDetect(t *testing.T) {
+ tests := []struct {
+ name string
+ godebug string
+ env map[string]string
+ systemFIPS bool
+ wantEnabled bool
+ wantMessage string
+ }{
+ // GODEBUG=fips140 takes precedence over everything else.
+ {name: "GODEBUG=on", godebug: "on", wantEnabled: true, wantMessage: "environment variable GODEBUG=fips140=on"},
+ {name: "GODEBUG=only", godebug: "only", wantEnabled: true, wantMessage: "environment variable GODEBUG=fips140=only"},
+ {name: "GODEBUG=debug", godebug: "debug", wantEnabled: true, wantMessage: "environment variable GODEBUG=fips140=debug"},
+ {name: "GODEBUG=on beats GOFIPS=0 and kernel FIPS", godebug: "on", env: map[string]string{"GOFIPS": "0"}, systemFIPS: true, wantEnabled: true, wantMessage: "environment variable GODEBUG=fips140=on"},
+ {name: "GODEBUG=off beats kernel FIPS", godebug: "off", systemFIPS: true, wantEnabled: false, wantMessage: "environment variable GODEBUG=fips140=off"},
+ {name: "GODEBUG=off beats GOFIPS=1", godebug: "off", env: map[string]string{"GOFIPS": "1"}, wantEnabled: false, wantMessage: "environment variable GODEBUG=fips140=off"},
+
+ // GOFIPS=1 enables FIPS when GODEBUG is unset/empty/unrecognized.
+ {name: "GOFIPS=1", env: map[string]string{"GOFIPS": "1"}, wantEnabled: true, wantMessage: "environment variable GOFIPS=1"},
+ {name: "GOFIPS=1 beats kernel FIPS off", env: map[string]string{"GOFIPS": "1"}, systemFIPS: false, wantEnabled: true, wantMessage: "environment variable GOFIPS=1"},
+ {name: "GODEBUG unrecognized, GOFIPS=1", godebug: "bogus", env: map[string]string{"GOFIPS": "1"}, wantEnabled: true, wantMessage: "environment variable GOFIPS=1"},
+
+ // Non-"1" values of GOFIPS are ignored and fall through.
+ {name: "GOFIPS=0 falls through to kernel FIPS on", env: map[string]string{"GOFIPS": "0"}, systemFIPS: true, wantEnabled: true, wantMessage: "system FIPS mode"},
+ {name: "GOFIPS=0 falls through to kernel FIPS off", env: map[string]string{"GOFIPS": "0"}, systemFIPS: false, wantEnabled: false, wantMessage: ""},
+ {name: "GOFIPS empty falls through to kernel FIPS on", env: map[string]string{"GOFIPS": ""}, systemFIPS: true, wantEnabled: true, wantMessage: "system FIPS mode"},
+ {name: "GOFIPS=garbage falls through", env: map[string]string{"GOFIPS": "garbage"}, systemFIPS: false, wantEnabled: false, wantMessage: ""},
+
+ // GOLANG_FIPS behaves the same as GOFIPS.
+ {name: "GOLANG_FIPS=1", env: map[string]string{"GOLANG_FIPS": "1"}, wantEnabled: true, wantMessage: "environment variable GOLANG_FIPS=1"},
+ {name: "GOFIPS=1 beats GOLANG_FIPS=0", env: map[string]string{"GOFIPS": "1", "GOLANG_FIPS": "0"}, wantEnabled: true, wantMessage: "environment variable GOFIPS=1"},
+ {name: "GOLANG_FIPS=0 falls through to kernel FIPS on", env: map[string]string{"GOLANG_FIPS": "0"}, systemFIPS: true, wantEnabled: true, wantMessage: "system FIPS mode"},
+
+ // With nothing set, the kernel FIPS flag controls the result.
+ {name: "nothing set, kernel FIPS on", systemFIPS: true, wantEnabled: true, wantMessage: "system FIPS mode"},
+ {name: "nothing set, kernel FIPS off", systemFIPS: false, wantEnabled: false, wantMessage: ""},
+ }
+
+ for _, tc := range tests {
+ t.Run(tc.name, func(t *testing.T) {
+ systemFIPS := func() bool { return tc.systemFIPS }
+ gotEnabled, gotMessage := detect(tc.godebug, fakeEnv(tc.env), systemFIPS)
+ if gotEnabled != tc.wantEnabled || gotMessage != tc.wantMessage {
+ t.Errorf("detect(godebug=%q, env=%v, systemFIPS=%v) = (%v, %q), want (%v, %q)",
+ tc.godebug, tc.env, tc.systemFIPS,
+ gotEnabled, gotMessage, tc.wantEnabled, tc.wantMessage)
+ }
+ })
+ }
+}
diff --git a/src/crypto/internal/backend/fips140/isrequirefips.go b/src/crypto/internal/backend/fips140/isrequirefips.go
new file mode 100644
index 00000000000000..b33d08c84e2dae
Expand Down Expand Up @@ -3199,7 +3307,7 @@ index 00000000000000..7500bd3a86472b
+ `
+}
diff --git a/src/go/build/deps_test.go b/src/go/build/deps_test.go
index 2c523a20bdfbc7..b6ff825fc811b3 100644
index e8eeb9455e4bb5..52c0785a87e5e8 100644
--- a/src/go/build/deps_test.go
+++ b/src/go/build/deps_test.go
@@ -367,7 +367,7 @@ var depsRules = `
Expand Down Expand Up @@ -3236,7 +3344,7 @@ index 2c523a20bdfbc7..b6ff825fc811b3 100644
FIPS, internal/godebug, embed,
crypto/internal/boring/sig,
crypto/internal/boring/syso,
@@ -614,8 +625,15 @@ var depsRules = `
@@ -617,8 +628,15 @@ var depsRules = `
math/big, github.com/microsoft/go-crypto-darwin/xcrypto < github.com/microsoft/go-crypto-darwin/bbig;
math/big, github.com/microsoft/go-crypto-winnative/cng < github.com/microsoft/go-crypto-winnative/cng/bbig;

Expand Down
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