Add /proc/sys/kernel/shm[all,max,mni].

PiperOrigin-RevId: 210459956
Change-Id: I51859b90fa967631e0a54a390abc3b5541fbee66

pkg/abi/linux/shm.go

@@ -14,6 +14,8 @@
 
 package linux
 
+import "math"
+
 // shmat(2) flags. Source: include/uapi/linux/shm.h
 const (
 	SHM_RDONLY = 010000  // Read-only access.
@@ -38,6 +40,15 @@ const (
 	SHM_INFO   = 14
 )
 
+// SHM defaults as specified by linux. Source: include/uapi/linux/shm.h
+const (
+	SHMMIN = 1
+	SHMMNI = 4096
+	SHMMAX = math.MaxUint64 - 1<<24
+	SHMALL = math.MaxUint64 - 1<<24
+	SHMSEG = 4096
+)
+
 // ShmidDS is equivalent to struct shmid64_ds. Source:
 // include/uapi/asm-generic/shmbuf.h
 type ShmidDS struct {

pkg/sentry/fs/proc/sys.go

@@ -17,7 +17,9 @@ package proc
 import (
 	"fmt"
 	"io"
+	"strconv"
 
+	"gvisor.googlesource.com/gvisor/pkg/abi/linux"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/context"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/fs"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/fs/proc/seqfile"
@@ -102,6 +104,10 @@ func (p *proc) newKernelDir(ctx context.Context, msrc *fs.MountSource) *fs.Inode
 	d := &ramfs.Dir{}
 	d.InitDir(ctx, nil, fs.RootOwner, fs.FilePermsFromMode(0555))
 	d.AddChild(ctx, "hostname", p.newHostname(ctx, msrc))
+
+	d.AddChild(ctx, "shmmax", p.newStubProcFSFile(ctx, msrc, []byte(strconv.FormatUint(linux.SHMMAX, 10))))
+	d.AddChild(ctx, "shmall", p.newStubProcFSFile(ctx, msrc, []byte(strconv.FormatUint(linux.SHMALL, 10))))
+	d.AddChild(ctx, "shmmni", p.newStubProcFSFile(ctx, msrc, []byte(strconv.FormatUint(linux.SHMMNI, 10))))
 	return newFile(d, msrc, fs.SpecialDirectory, nil)
 }
 

pkg/sentry/kernel/shm/shm.go

@@ -35,7 +35,6 @@ package shm
 
 import (
 	"fmt"
-	"math"
 	"sync"
 
 	"gvisor.googlesource.com/gvisor/pkg/abi/linux"
@@ -52,23 +51,6 @@ import (
 	"gvisor.googlesource.com/gvisor/pkg/syserror"
 )
 
-// Various limits for shared memory segments.
-const (
-	// shmsTotalMaxPages is the system-wide limit on all shared memory segments, measured
-	// in number of pages.
-	shmsTotalMaxPages = math.MaxInt64 // SHMALL
-
-	// shmMaxSize is the maximum size of a single segment, in bytes.
-	shmMaxSize = math.MaxInt64 // SHMMAX
-
-	// shmMinSize is the minimum specifiable size of a segment, effectively
-	// yielding a size rounded up to the next page size. Measured in bytes.
-	shmMinSize = 1 // SHMMIN
-
-	// shmsTotalMax is the maximum number of segments on the system.
-	shmsTotalMax = 4096 // SHMMNI
-)
-
 // Registry tracks all shared memory segments in an IPC namespace. The registry
 // provides the mechanisms for creating and finding segments, and reporting
 // global shm parameters.
@@ -119,7 +101,7 @@ func (r *Registry) findByKey(key int32) *Shm {
 // FindOrCreate looks up or creates a segment in the registry. It's functionally
 // analogous to open(2).
 func (r *Registry) FindOrCreate(ctx context.Context, pid, key int32, size uint64, mode linux.FileMode, private, create, exclusive bool) (*Shm, error) {
-	if create && (size < shmMinSize || size > shmMaxSize) {
+	if create && (size < linux.SHMMIN || size > linux.SHMMAX) {
 		// "A new segment was to be created and size is less than SHMMIN or
 		// greater than SHMMAX." - man shmget(2)
 		return nil, syserror.EINVAL
@@ -128,7 +110,7 @@ func (r *Registry) FindOrCreate(ctx context.Context, pid, key int32, size uint64
 	r.mu.Lock()
 	defer r.mu.Unlock()
 
-	if len(r.shms) >= shmsTotalMax {
+	if len(r.shms) >= linux.SHMMNI {
 		// "All possible shared memory IDs have been taken (SHMMNI) ..."
 		//   - man shmget(2)
 		return nil, syserror.ENOSPC
@@ -179,7 +161,7 @@ func (r *Registry) FindOrCreate(ctx context.Context, pid, key int32, size uint64
 		return nil, syserror.EINVAL
 	}
 
-	if numPages := sizeAligned / usermem.PageSize; r.totalPages+numPages > shmsTotalMaxPages {
+	if numPages := sizeAligned / usermem.PageSize; r.totalPages+numPages > linux.SHMALL {
 		// "... allocating a segment of the requested size would cause the
 		// system to exceed the system-wide limit on shared memory (SHMALL)."
 		//   - man shmget(2)
@@ -245,11 +227,11 @@ func (r *Registry) newShm(ctx context.Context, pid, key int32, creator fs.FileOw
 // system. See shmctl(IPC_INFO).
 func (r *Registry) IPCInfo() *linux.ShmParams {
 	return &linux.ShmParams{
-		ShmMax: shmMaxSize,
-		ShmMin: shmMinSize,
-		ShmMni: shmsTotalMax,
-		ShmSeg: shmsTotalMax, // Linux also sets this to SHMMNI.
-		ShmAll: shmsTotalMaxPages,
+		ShmMax: linux.SHMMAX,
+		ShmMin: linux.SHMMIN,
+		ShmMni: linux.SHMMNI,
+		ShmSeg: linux.SHMSEG,
+		ShmAll: linux.SHMALL,
 	}
 }