procfs: add KernelTainted() to parse /proc/sys/kernel/tainted

Signed-off-by: Arun S <arun.srinivasan@flipkart.com>

Author: Arun S

kernel_tainted.go

@@ -0,0 +1,115 @@
+// Copyright The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//go:build !windows
+
+package procfs
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"strconv"
+	"strings"
+
+	"github.com/prometheus/procfs/internal/util"
+)
+
+// KernelTaintBit represents a single kernel taint flag.
+type KernelTaintBit struct {
+	// Index is the zero-based bit position in the tainted bitmask.
+	Index int
+	// Flag is the letter code identifying this taint (e.g. "L" for soft lockup).
+	// See https://www.kernel.org/doc/html/latest/admin-guide/tainted-kernels.html
+	Flag string
+	// Description is a human-readable explanation of what this taint means.
+	Description string
+	// Set indicates whether this taint flag is currently active.
+	Set bool
+}
+
+// KernelTainted holds the kernel taint state read from /proc/sys/kernel/tainted.
+type KernelTainted struct {
+	// Value is the raw integer from /proc/sys/kernel/tainted.
+	Value uint64
+	// Bits contains each known taint flag and whether it is currently set.
+	// Flags are listed in bit-position order (bit 0 first).
+	Bits []KernelTaintBit
+}
+
+// kernelTaintBitDefs lists all known kernel taint flags in bit-position order.
+// Reference: https://www.kernel.org/doc/html/latest/admin-guide/tainted-kernels.html
+var kernelTaintBitDefs = []struct {
+	flag        string
+	description string
+}{
+	{"P", "Proprietary module was loaded."},
+	{"F", "Module was force loaded."},
+	{"S", "SMP kernel oops on an officially SMP incapable processor."},
+	{"R", "Module was force unloaded."},
+	{"M", "Processor reported a Machine Check Exception (MCE)."},
+	{"B", "Bad page referenced or some unexpected page flags."},
+	{"U", "Taint requested by userspace application."},
+	{"D", "Kernel died recently, i.e. there was an OOPS or BUG."},
+	{"A", "An ACPI table was overridden by user."},
+	{"W", "Kernel issued warning."},
+	{"C", "Staging driver was loaded."},
+	{"I", "Workaround for bug in platform firmware applied."},
+	{"O", "Externally-built (out-of-tree) module was loaded."},
+	{"E", "Unsigned module was loaded."},
+	{"L", "Soft lockup occurred."},
+	{"K", "Kernel has been live patched."},
+	{"X", "Auxiliary taint, defined and used by distros."},
+	{"T", "The kernel was built with the struct randomization plugin."},
+	{"N", "An in-kernel test such as a KUnit test has been run."},
+	{"J", "Userspace used a mutating debug operation in fwctl."},
+}
+
+// KernelTainted reads /proc/sys/kernel/tainted and returns the raw taint value
+// along with each known flag parsed into a KernelTainted struct.
+// See https://www.kernel.org/doc/html/latest/admin-guide/tainted-kernels.html
+func (fs FS) KernelTainted() (KernelTainted, error) {
+	data, err := util.ReadFileNoStat(fs.proc.Path("sys", "kernel", "tainted"))
+	if err != nil {
+		return KernelTainted{}, err
+	}
+	return parseTainted(bytes.NewReader(data))
+}
+
+// parseTainted parses the content of /proc/sys/kernel/tainted.
+func parseTainted(r io.Reader) (KernelTainted, error) {
+	data, err := io.ReadAll(r)
+	if err != nil {
+		return KernelTainted{}, err
+	}
+
+	value, err := strconv.ParseUint(strings.TrimSpace(string(data)), 10, 64)
+	if err != nil {
+		return KernelTainted{}, fmt.Errorf("couldn't parse tainted value: %w", err)
+	}
+
+	bits := make([]KernelTaintBit, len(kernelTaintBitDefs))
+	for i, def := range kernelTaintBitDefs {
+		bits[i] = KernelTaintBit{
+			Index:       i,
+			Flag:        def.flag,
+			Description: def.description,
+			Set:         value&(1<<uint(i)) != 0,
+		}
+	}
+
+	return KernelTainted{
+		Value: value,
+		Bits:  bits,
+	}, nil
+}

kernel_tainted_test.go

@@ -0,0 +1,89 @@
+// Copyright The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//go:build !windows
+
+package procfs
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestKernelTainted(t *testing.T) {
+	fs, err := NewFS(procfsFixtures)
+	if err != nil {
+		t.Fatalf("failed to access %s: %v", procfsFixtures, err)
+	}
+
+	tainted, err := fs.KernelTainted()
+	if err != nil {
+		t.Fatalf("failed to collect %s/sys/kernel/tainted: %v", procfsFixtures, err)
+	}
+
+	// Fixture value is 12288 = bit 12 (O) + bit 13 (E).
+	if tainted.Value != 12288 {
+		t.Errorf("tainted value: want %d, got %d", 12288, tainted.Value)
+	}
+
+	const wantBits = 20
+	if len(tainted.Bits) != wantBits {
+		t.Fatalf("tainted bits length: want %d, got %d", wantBits, len(tainted.Bits))
+	}
+
+	for _, tc := range []struct {
+		index int
+		flag  string
+		set   bool
+	}{
+		{0, "P", false},
+		{12, "O", true},  // Externally-built (out-of-tree) module
+		{13, "E", true},  // Unsigned module
+		{14, "L", false}, // Soft lockup — must be clear
+		{17, "T", false},
+		{18, "N", false},
+		{19, "J", false},
+	} {
+		b := tainted.Bits[tc.index]
+		if b.Index != tc.index {
+			t.Errorf("bit[%d].Index: want %d, got %d", tc.index, tc.index, b.Index)
+		}
+		if b.Flag != tc.flag {
+			t.Errorf("bit[%d].Flag: want %q, got %q", tc.index, tc.flag, b.Flag)
+		}
+		if b.Set != tc.set {
+			t.Errorf("bit[%d] (%s): want Set=%v, got Set=%v", tc.index, tc.flag, tc.set, b.Set)
+		}
+	}
+}
+
+func TestParseTainted(t *testing.T) {
+	// Test parsing directly without filesystem access.
+	tainted, err := parseTainted(strings.NewReader("16384\n"))
+	if err != nil {
+		t.Fatalf("parseTainted failed: %v", err)
+	}
+
+	// 16384 = 2^14 → only bit 14 (L, soft lockup) should be set.
+	if tainted.Value != 16384 {
+		t.Errorf("value: want 16384, got %d", tainted.Value)
+	}
+	if !tainted.Bits[14].Set {
+		t.Errorf("bit 14 (L): want Set=true, got false")
+	}
+	for i, b := range tainted.Bits {
+		if i != 14 && b.Set {
+			t.Errorf("bit %d (%s): want Set=false, got true", i, b.Flag)
+		}
+	}
+}

testdata/fixtures.ttar

@@ -3465,6 +3465,11 @@ Lines: 1
 kill_process kill_thread trap errno trace log allow
 Mode: 644
 # ttar - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+Path: fixtures/proc/sys/kernel/tainted
+Lines: 1
+12288
+Mode: 444
+# ttar - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 Directory: fixtures/proc/sys/vm
 Mode: 755
 # ttar - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -