runtime: add page tracer

This change adds a new GODEBUG flag called pagetrace that writes a
low-overhead trace of how pages of memory are managed by the Go runtime.

The page tracer is kept behind a GOEXPERIMENT flag due to a potential
security risk for setuid binaries.

Change-Id: I6f4a2447d02693c25214400846a5d2832ad6e5c0
Reviewed-on: https://go-review.googlesource.com/c/go/+/444157
Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: David Chase <drchase@google.com>
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

src/internal/goexperiment/flags.go

@@ -94,4 +94,10 @@ type Flags struct {
 	// Arenas causes the "arena" standard library package to be visible
 	// to the outside world.
 	Arenas bool
+
+	// PageTrace enables GODEBUG=pagetrace=/path/to/result. This feature
+	// is a GOEXPERIMENT due to a security risk with setuid binaries:
+	// this compels the Go runtime to write to some arbitrary file, which
+	// may be exploited.
+	PageTrace bool
 }

src/runtime/create_file_nounix.go

@@ -0,0 +1,14 @@
+// Copyright 2022 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.
+
+//go:build !unix
+
+package runtime
+
+const canCreateFile = false
+
+func create(name *byte, perm int32) int32 {
+	throw("unimplemented")
+	return -1
+}

src/runtime/create_file_unix.go

@@ -0,0 +1,14 @@
+// Copyright 2022 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.
+
+//go:build unix
+
+package runtime
+
+const canCreateFile = true
+
+// create returns an fd to a write-only file.
+func create(name *byte, perm int32) int32 {
+	return open(name, _O_CREAT|_O_WRONLY|_O_TRUNC, perm)
+}

src/runtime/defs1_netbsd_386.go

@@ -8,7 +8,10 @@ const (
 	_EFAULT = 0xe
 	_EAGAIN = 0x23
 
+	_O_WRONLY   = 0x1
 	_O_NONBLOCK = 0x4
+	_O_CREAT    = 0x200
+	_O_TRUNC    = 0x400
 	_O_CLOEXEC  = 0x400000
 
 	_PROT_NONE  = 0x0

src/runtime/defs1_netbsd_amd64.go

@@ -8,7 +8,10 @@ const (
 	_EFAULT = 0xe
 	_EAGAIN = 0x23
 
+	_O_WRONLY   = 0x1
 	_O_NONBLOCK = 0x4
+	_O_CREAT    = 0x200
+	_O_TRUNC    = 0x400
 	_O_CLOEXEC  = 0x400000
 
 	_PROT_NONE  = 0x0

src/runtime/defs1_netbsd_arm.go

@@ -8,7 +8,10 @@ const (
 	_EFAULT = 0xe
 	_EAGAIN = 0x23
 
+	_O_WRONLY   = 0x1
 	_O_NONBLOCK = 0x4
+	_O_CREAT    = 0x200
+	_O_TRUNC    = 0x400
 	_O_CLOEXEC  = 0x400000
 
 	_PROT_NONE  = 0x0

src/runtime/defs1_netbsd_arm64.go

@@ -8,7 +8,10 @@ const (
 	_EFAULT = 0xe
 	_EAGAIN = 0x23
 
+	_O_WRONLY   = 0x1
 	_O_NONBLOCK = 0x4
+	_O_CREAT    = 0x200
+	_O_TRUNC    = 0x400
 	_O_CLOEXEC  = 0x400000
 
 	_PROT_NONE  = 0x0

src/runtime/defs1_solaris_amd64.go

@@ -91,7 +91,10 @@ const (
 
 	_MAXHOSTNAMELEN = 0x100
 
+	_O_WRONLY   = 0x1
 	_O_NONBLOCK = 0x80
+	_O_TRUNC    = 0x200
+	_O_CREAT    = 0x100
 	_O_CLOEXEC  = 0x800000
 	_FD_CLOEXEC = 0x1
 	_F_GETFL    = 0x3

src/runtime/defs_aix.go

@@ -124,7 +124,10 @@ const (
 	_ITIMER_PROF    = C.ITIMER_PROF
 
 	_O_RDONLY   = C.O_RDONLY
+	_O_WRONLY   = C.O_WRONLY
 	_O_NONBLOCK = C.O_NONBLOCK
+	_O_CREAT    = C.O_CREAT
+	_O_TRUNC    = C.O_TRUNC
 
 	_SS_DISABLE  = C.SS_DISABLE
 	_SI_USER     = C.SI_USER

src/runtime/defs_aix_ppc64.go

@@ -81,7 +81,10 @@ const (
 	_ITIMER_PROF    = 0x2
 
 	_O_RDONLY   = 0x0
+	_O_WRONLY   = 0x1
 	_O_NONBLOCK = 0x4
+	_O_CREAT    = 0x100
+	_O_TRUNC    = 0x200
 
 	_SS_DISABLE  = 0x2
 	_SI_USER     = 0x0

src/runtime/defs_darwin.go

@@ -120,7 +120,10 @@ const (
 	F_SETFL    = C.F_SETFL
 	FD_CLOEXEC = C.FD_CLOEXEC
 
+	O_WRONLY   = C.O_WRONLY
 	O_NONBLOCK = C.O_NONBLOCK
+	O_CREAT    = C.O_CREAT
+	O_TRUNC    = C.O_TRUNC
 )
 
 type StackT C.struct_sigaltstack

src/runtime/defs_darwin_amd64.go

@@ -99,7 +99,10 @@ const (
 	_F_SETFL    = 0x4
 	_FD_CLOEXEC = 0x1
 
-	_O_NONBLOCK = 4
+	_O_WRONLY   = 0x1
+	_O_NONBLOCK = 0x4
+	_O_CREAT    = 0x200
+	_O_TRUNC    = 0x400
 )
 
 type stackt struct {

src/runtime/defs_darwin_arm64.go

@@ -101,7 +101,10 @@ const (
 	_F_SETFL    = 0x4
 	_FD_CLOEXEC = 0x1
 
-	_O_NONBLOCK = 4
+	_O_WRONLY   = 0x1
+	_O_NONBLOCK = 0x4
+	_O_CREAT    = 0x200
+	_O_TRUNC    = 0x400
 )
 
 type stackt struct {

src/runtime/defs_dragonfly.go

@@ -32,7 +32,10 @@ const (
 	EBUSY  = C.EBUSY
 	EAGAIN = C.EAGAIN
 
+	O_WRONLY   = C.O_WRONLY
 	O_NONBLOCK = C.O_NONBLOCK
+	O_CREAT    = C.O_CREAT
+	O_TRUNC    = C.O_TRUNC
 	O_CLOEXEC  = C.O_CLOEXEC
 
 	PROT_NONE  = C.PROT_NONE

src/runtime/defs_dragonfly_amd64.go

@@ -11,7 +11,10 @@ const (
 	_EBUSY  = 0x10
 	_EAGAIN = 0x23
 
+	_O_WRONLY   = 0x1
 	_O_NONBLOCK = 0x4
+	_O_CREAT    = 0x200
+	_O_TRUNC    = 0x400
 	_O_CLOEXEC  = 0x20000
 
 	_PROT_NONE  = 0x0

src/runtime/defs_freebsd.go

@@ -51,7 +51,10 @@ const (
 	EAGAIN    = C.EAGAIN
 	ETIMEDOUT = C.ETIMEDOUT
 
+	O_WRONLY   = C.O_WRONLY
 	O_NONBLOCK = C.O_NONBLOCK
+	O_CREAT    = C.O_CREAT
+	O_TRUNC    = C.O_TRUNC
 	O_CLOEXEC  = C.O_CLOEXEC
 
 	PROT_NONE  = C.PROT_NONE

src/runtime/defs_freebsd_riscv64.go

@@ -18,7 +18,10 @@ const (
 	_EAGAIN    = 0x23
 	_ETIMEDOUT = 0x3c
 
+	_O_WRONLY   = 0x1
 	_O_NONBLOCK = 0x4
+	_O_CREAT    = 0x200
+	_O_TRUNC    = 0x400
 	_O_CLOEXEC  = 0x100000
 
 	_PROT_NONE  = 0x0

src/runtime/defs_linux_386.go

@@ -90,6 +90,9 @@ const (
 	_SIGEV_THREAD_ID = 0x4
 
 	_O_RDONLY   = 0x0
+	_O_WRONLY   = 0x1
+	_O_CREAT    = 0x40
+	_O_TRUNC    = 0x200
 	_O_NONBLOCK = 0x800
 	_O_CLOEXEC  = 0x80000
 

src/runtime/defs_linux_amd64.go

@@ -165,6 +165,9 @@ type sigevent struct {
 
 const (
 	_O_RDONLY   = 0x0
+	_O_WRONLY   = 0x1
+	_O_CREAT    = 0x40
+	_O_TRUNC    = 0x200
 	_O_NONBLOCK = 0x800
 	_O_CLOEXEC  = 0x80000
 )

src/runtime/defs_linux_arm.go

@@ -80,6 +80,9 @@ const (
 	_ITIMER_PROF    = 0x2
 	_ITIMER_VIRTUAL = 0x1
 	_O_RDONLY       = 0
+	_O_WRONLY       = 0x1
+	_O_CREAT        = 0x40
+	_O_TRUNC        = 0x200
 	_O_NONBLOCK     = 0x800
 	_O_CLOEXEC      = 0x80000
 

src/runtime/defs_linux_arm64.go

@@ -165,6 +165,9 @@ type sigevent struct {
 
 const (
 	_O_RDONLY   = 0x0
+	_O_WRONLY   = 0x1
+	_O_CREAT    = 0x40
+	_O_TRUNC    = 0x200
 	_O_NONBLOCK = 0x800
 	_O_CLOEXEC  = 0x80000
 )

src/runtime/defs_linux_loong64.go

@@ -137,6 +137,9 @@ type sigevent struct {
 
 const (
 	_O_RDONLY   = 0x0
+	_O_WRONLY   = 0x1
+	_O_CREAT    = 0x40
+	_O_TRUNC    = 0x200
 	_O_NONBLOCK = 0x800
 	_O_CLOEXEC  = 0x80000
 )

src/runtime/defs_linux_mips64x.go

@@ -169,6 +169,9 @@ type sigevent struct {
 
 const (
 	_O_RDONLY    = 0x0
+	_O_WRONLY    = 0x1
+	_O_CREAT     = 0x100
+	_O_TRUNC     = 0x200
 	_O_NONBLOCK  = 0x80
 	_O_CLOEXEC   = 0x80000
 	_SA_RESTORER = 0

src/runtime/defs_linux_mipsx.go

@@ -163,7 +163,10 @@ type sigevent struct {
 
 const (
 	_O_RDONLY    = 0x0
+	_O_WRONLY    = 0x1
 	_O_NONBLOCK  = 0x80
+	_O_CREAT     = 0x100
+	_O_TRUNC     = 0x200
 	_O_CLOEXEC   = 0x80000
 	_SA_RESTORER = 0
 )

src/runtime/defs_linux_ppc64.go

@@ -166,6 +166,9 @@ type sigevent struct {
 
 const (
 	_O_RDONLY    = 0x0
+	_O_WRONLY    = 0x1
+	_O_CREAT     = 0x40
+	_O_TRUNC     = 0x200
 	_O_NONBLOCK  = 0x800
 	_O_CLOEXEC   = 0x80000
 	_SA_RESTORER = 0

src/runtime/defs_linux_ppc64le.go

@@ -166,6 +166,9 @@ type sigevent struct {
 
 const (
 	_O_RDONLY    = 0x0
+	_O_WRONLY    = 0x1
+	_O_CREAT     = 0x40
+	_O_TRUNC     = 0x200
 	_O_NONBLOCK  = 0x800
 	_O_CLOEXEC   = 0x80000
 	_SA_RESTORER = 0

src/runtime/defs_linux_riscv64.go

@@ -162,6 +162,9 @@ type sigevent struct {
 
 const (
 	_O_RDONLY   = 0x0
+	_O_WRONLY   = 0x1
+	_O_CREAT    = 0x40
+	_O_TRUNC    = 0x200
 	_O_NONBLOCK = 0x800
 	_O_CLOEXEC  = 0x80000
 )

src/runtime/defs_linux_s390x.go

@@ -159,6 +159,9 @@ type sigevent struct {
 
 const (
 	_O_RDONLY    = 0x0
+	_O_WRONLY    = 0x1
+	_O_CREAT     = 0x40
+	_O_TRUNC     = 0x200
 	_O_NONBLOCK  = 0x800
 	_O_CLOEXEC   = 0x80000
 	_SA_RESTORER = 0

src/runtime/defs_netbsd.go

@@ -34,7 +34,10 @@ const (
 	EFAULT = C.EFAULT
 	EAGAIN = C.EAGAIN
 
+	O_WRONLY   = C.O_WRONLY
 	O_NONBLOCK = C.O_NONBLOCK
+	O_CREAT    = C.O_CREAT
+	O_TRUNC    = C.O_TRUNC
 	O_CLOEXEC  = C.O_CLOEXEC
 
 	PROT_NONE  = C.PROT_NONE

src/runtime/defs_openbsd_386.go

@@ -10,7 +10,10 @@ const (
 	_EFAULT = 0xe
 	_EAGAIN = 0x23
 
+	_O_WRONLY   = 0x1
 	_O_NONBLOCK = 0x4
+	_O_CREAT    = 0x200
+	_O_TRUNC    = 0x400
 	_O_CLOEXEC  = 0x10000
 
 	_PROT_NONE  = 0x0