Report total memory based on limit or host

gVisor was previously reporting the lower of cgroup limit or 2GB as total
memory. This may cause applications to make bad decisions based on amount
of memory available to them when more than 2GB is required.

This change makes the lower of cgroup limit or the host total memory to be
reported inside the sandbox. This also is more inline with docker which always
reports host total memory. Note that reporting cgroup limit is strictly better
than host total memory when there is a limit set.

Fixes #5608

PiperOrigin-RevId: 403241608

pkg/sentry/fsimpl/proc/tasks_files.go

@@ -262,9 +262,8 @@ var _ dynamicInode = (*meminfoData)(nil)
 
 // Generate implements vfs.DynamicBytesSource.Generate.
 func (*meminfoData) Generate(ctx context.Context, buf *bytes.Buffer) error {
-	k := kernel.KernelFromContext(ctx)
-	mf := k.MemoryFile()
-	mf.UpdateUsage()
+	mf := kernel.KernelFromContext(ctx).MemoryFile()
+	_ = mf.UpdateUsage() // Best effort
 	snapshot, totalUsage := usage.MemoryAccounting.Copy()
 	totalSize := usage.TotalMemory(mf.TotalSize(), totalUsage)
 	anon := snapshot.Anonymous + snapshot.Tmpfs

pkg/sentry/usage/memory.go

@@ -252,9 +252,9 @@ func (m *MemoryLocked) Copy() (MemoryStats, uint64) {
 	return ms, m.totalLocked()
 }
 
-// These options control how much total memory the is reported to the application.
-// They may only be set before the application starts executing, and must not
-// be modified.
+// These options control how much total memory the is reported to the
+// application. They may only be set before the application starts executing,
+// and must not be modified.
 var (
 	// MinimumTotalMemoryBytes is the minimum reported total system memory.
 	MinimumTotalMemoryBytes uint64 = 2 << 30 // 2 GB

runsc/boot/loader.go

@@ -340,6 +340,7 @@ func New(args Args) (*Loader, error) {
 	if args.TotalMem > 0 {
 		// Adjust the total memory returned by the Sentry so that applications that
 		// use /proc/meminfo can make allocations based on this limit.
+		usage.MinimumTotalMemoryBytes = args.TotalMem
 		usage.MaximumTotalMemoryBytes = args.TotalMem
 		log.Infof("Setting total memory to %.2f GB", float64(args.TotalMem)/(1<<30))
 	}

runsc/sandbox/BUILD

@@ -1,10 +1,11 @@
-load("//tools:defs.bzl", "go_library")
+load("//tools:defs.bzl", "go_library", "go_test")
 
 package(licenses = ["notice"])
 
 go_library(
     name = "sandbox",
     srcs = [
+        "memory.go",
         "network.go",
         "network_unsafe.go",
         "sandbox.go",
@@ -39,3 +40,10 @@ go_library(
         "@org_golang_x_sys//unix:go_default_library",
     ],
 )
+
+go_test(
+    name = "sandbox_test",
+    size = "small",
+    srcs = ["memory_test.go"],
+    library = ":sandbox",
+)

runsc/sandbox/memory.go

@@ -0,0 +1,70 @@
+// Copyright 2021 The gVisor 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.
+
+package sandbox
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"os"
+	"strconv"
+	"strings"
+)
+
+// totalSystemMemory extracts "MemTotal" from "/proc/meminfo".
+func totalSystemMemory() (uint64, error) {
+	f, err := os.Open("/proc/meminfo")
+	if err != nil {
+		return 0, err
+	}
+	defer f.Close()
+	return parseTotalSystemMemory(f)
+}
+
+func parseTotalSystemMemory(r io.Reader) (uint64, error) {
+	for scanner := bufio.NewScanner(r); scanner.Scan(); {
+		line := scanner.Text()
+		totalStr := strings.TrimPrefix(line, "MemTotal:")
+		if len(totalStr) < len(line) {
+			fields := strings.Fields(totalStr)
+			if len(fields) == 0 || len(fields) > 2 {
+				return 0, fmt.Errorf(`malformed "MemTotal": %q`, line)
+			}
+			totalStr = fields[0]
+			unit := ""
+			if len(fields) == 2 {
+				unit = fields[1]
+			}
+			mem, err := strconv.ParseUint(totalStr, 10, 64)
+			if err != nil {
+				return 0, err
+			}
+			switch unit {
+			case "":
+				// do nothing.
+			case "kB":
+				memKb := mem
+				mem = memKb * 1024
+				if mem < memKb {
+					return 0, fmt.Errorf(`"MemTotal" too large: %d`, memKb)
+				}
+			default:
+				return 0, fmt.Errorf("unknown unit %q: %q", unit, line)
+			}
+			return mem, nil
+		}
+	}
+	return 0, fmt.Errorf(`malformed "/proc/meminfo": "MemTotal" not found`)
+}

runsc/sandbox/memory_test.go

@@ -0,0 +1,91 @@
+// Copyright 2021 The gVisor 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.
+
+package sandbox
+
+import (
+	"bytes"
+	"fmt"
+	"math"
+	"strings"
+	"testing"
+)
+
+func TestTotalSystemMemory(t *testing.T) {
+	for _, tc := range []struct {
+		name    string
+		content string
+		want    uint64
+		err     string
+	}{
+		{
+			name:    "simple",
+			content: "MemTotal: 123\n",
+			want:    123,
+		},
+		{
+			name:    "kb",
+			content: "MemTotal: 123 kB\n",
+			want:    123 * 1024,
+		},
+		{
+			name:    "multi-line",
+			content: "Something: 123\nMemTotal: 456\nAnotherThing: 789\n",
+			want:    456,
+		},
+		{
+			name:    "not-found",
+			content: "Something: 123 kB\nAnotherThing: 789 kB\n",
+			err:     "not found",
+		},
+		{
+			name:    "no-number",
+			content: "MemTotal: \n",
+			err:     "malformed",
+		},
+		{
+			name:    "only-unit",
+			content: "MemTotal: kB\n",
+			err:     "invalid syntax",
+		},
+		{
+			name:    "negative",
+			content: "MemTotal: -1\n",
+			err:     "invalid syntax",
+		},
+		{
+			name:    "overflow",
+			content: fmt.Sprintf("MemTotal: %d kB\n", uint64(math.MaxUint64)),
+			err:     "too large",
+		},
+		{
+			name:    "unkown-unit",
+			content: "MemTotal: 123 mB\n",
+			err:     "unknown unit",
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			mem, err := parseTotalSystemMemory(bytes.NewReader([]byte(tc.content)))
+			if len(tc.err) > 0 {
+				if err == nil || !strings.Contains(err.Error(), tc.err) {
+					t.Errorf("parseTotalSystemMemory(%q) invalid error: %v, want: %v", tc.content, err, tc.err)
+				}
+			} else {
+				if tc.want != mem {
+					t.Errorf("parseTotalSystemMemory(%q) got: %v, want: %v", tc.content, mem, tc.want)
+				}
+			}
+		})
+	}
+}

runsc/sandbox/sandbox.go

@@ -758,6 +758,11 @@ func (s *Sandbox) createSandboxProcess(conf *config.Config, args *Args, startSyn
 	// shown as `exe`.
 	cmd.Args[0] = "runsc-sandbox"
 
+	mem, err := totalSystemMemory()
+	if err != nil {
+		return err
+	}
+
 	if s.Cgroup != nil {
 		cpuNum, err := s.Cgroup.NumCPU()
 		if err != nil {
@@ -785,16 +790,15 @@ func (s *Sandbox) createSandboxProcess(conf *config.Config, args *Args, startSyn
 		}
 		cmd.Args = append(cmd.Args, "--cpu-num", strconv.Itoa(cpuNum))
 
-		mem, err := s.Cgroup.MemoryLimit()
+		memLimit, err := s.Cgroup.MemoryLimit()
 		if err != nil {
 			return fmt.Errorf("getting memory limit from cgroups: %v", err)
 		}
-		// When memory limit is unset, a "large" number is returned. In that case,
-		// just stick with the default.
-		if mem < 0x7ffffffffffff000 {
-			cmd.Args = append(cmd.Args, "--total-memory", strconv.FormatUint(mem, 10))
+		if memLimit < mem {
+			mem = memLimit
 		}
 	}
+	cmd.Args = append(cmd.Args, "--total-memory", strconv.FormatUint(mem, 10))
 
 	if args.UserLog != "" {
 		f, err := os.OpenFile(args.UserLog, os.O_WRONLY|os.O_CREATE|os.O_APPEND, 0664)

test/e2e/integration_test.go

@@ -29,6 +29,7 @@ import (
 	"net"
 	"net/http"
 	"os"
+	"os/exec"
 	"path/filepath"
 	"regexp"
 	"strconv"
@@ -41,8 +42,12 @@ import (
 	"gvisor.dev/gvisor/pkg/test/testutil"
 )
 
-// defaultWait is the default wait time used for tests.
-const defaultWait = time.Minute
+const (
+	// defaultWait is the default wait time used for tests.
+	defaultWait = time.Minute
+
+	memInfoCmd = "cat /proc/meminfo | grep MemTotal: | awk '{print $2}'"
+)
 
 func TestMain(m *testing.M) {
 	dockerutil.EnsureSupportedDockerVersion()
@@ -255,16 +260,47 @@ func TestConnectToSelf(t *testing.T) {
 	}
 }
 
+func TestMemory(t *testing.T) {
+	// Find total amount of memory in the host.
+	host, err := exec.Command("sh", "-c", memInfoCmd).CombinedOutput()
+	if err != nil {
+		t.Fatal(err)
+	}
+	want, err := strconv.ParseUint(strings.TrimSpace(string(host)), 10, 64)
+	if err != nil {
+		t.Fatalf("failed to parse %q: %v", host, err)
+	}
+
+	ctx := context.Background()
+	d := dockerutil.MakeContainer(ctx, t)
+	defer d.CleanUp(ctx)
+
+	out, err := d.Run(ctx, dockerutil.RunOpts{Image: "basic/alpine"}, "sh", "-c", memInfoCmd)
+	if err != nil {
+		t.Fatalf("docker run failed: %v", err)
+	}
+
+	// Get memory from inside the container and ensure it matches the host.
+	got, err := strconv.ParseUint(strings.TrimSpace(out), 10, 64)
+	if err != nil {
+		t.Fatalf("failed to parse %q: %v", out, err)
+	}
+	if got != want {
+		t.Errorf("MemTotal got: %d, want: %d", got, want)
+	}
+}
+
 func TestMemLimit(t *testing.T) {
 	ctx := context.Background()
 	d := dockerutil.MakeContainer(ctx, t)
 	defer d.CleanUp(ctx)
 
 	allocMemoryKb := 50 * 1024
-	out, err := d.Run(ctx, dockerutil.RunOpts{
+	opts := dockerutil.RunOpts{
 		Image:  "basic/alpine",
 		Memory: allocMemoryKb * 1024, // In bytes.
-	}, "sh", "-c", "cat /proc/meminfo | grep MemTotal: | awk '{print $2}'")
+	}
+	out, err := d.Run(ctx, opts, "sh", "-c", memInfoCmd)
 	if err != nil {
 		t.Fatalf("docker run failed: %v", err)
 	}