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

5 files changed, 180 insertions, 6 deletions

diff --git a/runsc/boot/loader.go b/runsc/boot/loader.go
index 2f2d4df5e..28dbbcf1f 100644
--- a/runsc/boot/loader.go
+++ b/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))
 	}
diff --git a/runsc/sandbox/BUILD b/runsc/sandbox/BUILD
index d625230dd..bca14c7b8 100644
--- a/runsc/sandbox/BUILD
+++ b/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",
+)
diff --git a/runsc/sandbox/memory.go b/runsc/sandbox/memory.go
new file mode 100644
index 000000000..77b88eb89
--- /dev/null
+++ b/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`)
+}
diff --git a/runsc/sandbox/memory_test.go b/runsc/sandbox/memory_test.go
new file mode 100644
index 000000000..81dc67881
--- /dev/null
+++ b/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)
+				}
+			}
+		})
+	}
+}
diff --git a/runsc/sandbox/sandbox.go b/runsc/sandbox/sandbox.go
index f4a37cedc..714919139 100644
--- a/runsc/sandbox/sandbox.go
+++ b/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)