windows: use Go-managed pointer list for ProcThreadAttributeList
It turns out that if you write Go pointers to Go memory, the Go compiler
must be involved so that it generates various calls to the GC in the
process. Letting Windows write Go pointers to Go memory violated this.
We fix this by having all the Windows-managed memory be just a boring
[]byte blob. Then, in order to prevent the GC from prematurely cleaning
up the pointers referenced by that []byte blob, or in the future moving
memory and attempting to fix up pointers, we copy the data to the
Windows heap and then maintain a little array of pointers that have been
used. Every time the Update function is called with a new pointer, we
make a copy and append it to the list. Then, on Delete, we free the
pointers from the Windows heap.
Updates golang/go#44900.
Change-Id: I42340a93fd9f6b8d10340634cf833fd4559a5f4f
Reviewed-on: https://go-review.googlesource.com/c/sys/+/300369
Trust: Jason A. Donenfeld <Jason@zx2c4.com>
Run-TryBot: Jason A. Donenfeld <Jason@zx2c4.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
diff --git a/windows/exec_windows.go b/windows/exec_windows.go
index a020cae..7a11e83 100644
--- a/windows/exec_windows.go
+++ b/windows/exec_windows.go
@@ -9,6 +9,8 @@
import (
errorspkg "errors"
"unsafe"
+
+ "golang.org/x/sys/internal/unsafeheader"
)
// EscapeArg rewrites command line argument s as prescribed
@@ -135,8 +137,8 @@
}
}
-// NewProcThreadAttributeList allocates a new ProcThreadAttributeList, with the requested maximum number of attributes.
-func NewProcThreadAttributeList(maxAttrCount uint32) (*ProcThreadAttributeList, error) {
+// NewProcThreadAttributeList allocates a new ProcThreadAttributeListContainer, with the requested maximum number of attributes.
+func NewProcThreadAttributeList(maxAttrCount uint32) (*ProcThreadAttributeListContainer, error) {
var size uintptr
err := initializeProcThreadAttributeList(nil, maxAttrCount, 0, &size)
if err != ERROR_INSUFFICIENT_BUFFER {
@@ -145,10 +147,9 @@
}
return nil, err
}
- const psize = unsafe.Sizeof(uintptr(0))
// size is guaranteed to be ≥1 by InitializeProcThreadAttributeList.
- al := (*ProcThreadAttributeList)(unsafe.Pointer(&make([]unsafe.Pointer, (size+psize-1)/psize)[0]))
- err = initializeProcThreadAttributeList(al, maxAttrCount, 0, &size)
+ al := &ProcThreadAttributeListContainer{data: (*ProcThreadAttributeList)(unsafe.Pointer(&make([]byte, size)[0]))}
+ err = initializeProcThreadAttributeList(al.data, maxAttrCount, 0, &size)
if err != nil {
return nil, err
}
@@ -156,11 +157,39 @@
}
// Update modifies the ProcThreadAttributeList using UpdateProcThreadAttribute.
-func (al *ProcThreadAttributeList) Update(attribute uintptr, flags uint32, value unsafe.Pointer, size uintptr, prevValue unsafe.Pointer, returnedSize *uintptr) error {
- return updateProcThreadAttribute(al, flags, attribute, value, size, prevValue, returnedSize)
+// Note that the value passed to this function will be copied into memory
+// allocated by LocalAlloc, the contents of which should not contain any
+// Go-managed pointers, even if the passed value itself is a Go-managed
+// pointer.
+func (al *ProcThreadAttributeListContainer) Update(attribute uintptr, value unsafe.Pointer, size uintptr) error {
+ alloc, err := LocalAlloc(LMEM_FIXED, uint32(size))
+ if err != nil {
+ return err
+ }
+ var src, dst []byte
+ hdr := (*unsafeheader.Slice)(unsafe.Pointer(&src))
+ hdr.Data = value
+ hdr.Cap = int(size)
+ hdr.Len = int(size)
+ hdr = (*unsafeheader.Slice)(unsafe.Pointer(&dst))
+ hdr.Data = unsafe.Pointer(alloc)
+ hdr.Cap = int(size)
+ hdr.Len = int(size)
+ copy(dst, src)
+ al.heapAllocations = append(al.heapAllocations, alloc)
+ return updateProcThreadAttribute(al.data, 0, attribute, unsafe.Pointer(alloc), size, nil, nil)
}
// Delete frees ProcThreadAttributeList's resources.
-func (al *ProcThreadAttributeList) Delete() {
- deleteProcThreadAttributeList(al)
+func (al *ProcThreadAttributeListContainer) Delete() {
+ deleteProcThreadAttributeList(al.data)
+ for i := range al.heapAllocations {
+ LocalFree(Handle(al.heapAllocations[i]))
+ }
+ al.heapAllocations = nil
+}
+
+// List returns the actual ProcThreadAttributeList to be passed to StartupInfoEx.
+func (al *ProcThreadAttributeListContainer) List() *ProcThreadAttributeList {
+ return al.data
}
diff --git a/windows/syscall_windows_test.go b/windows/syscall_windows_test.go
index d6571b7..0aaa0a3 100644
--- a/windows/syscall_windows_test.go
+++ b/windows/syscall_windows_test.go
@@ -18,7 +18,6 @@
"strings"
"syscall"
"testing"
- "time"
"unsafe"
"golang.org/x/sys/windows"
@@ -506,39 +505,6 @@
}
}
-func TestProcThreadAttributeListPointers(t *testing.T) {
- list, err := windows.NewProcThreadAttributeList(1)
- if err != nil {
- t.Errorf("unable to create ProcThreadAttributeList: %v", err)
- }
- done := make(chan struct{})
- fds := make([]syscall.Handle, 20)
- runtime.SetFinalizer(&fds[0], func(*syscall.Handle) {
- close(done)
- })
- err = list.Update(windows.PROC_THREAD_ATTRIBUTE_HANDLE_LIST, 0, unsafe.Pointer(&fds[0]), uintptr(len(fds))*unsafe.Sizeof(fds[0]), nil, nil)
- if err != nil {
- list.Delete()
- t.Errorf("unable to update ProcThreadAttributeList: %v", err)
- return
- }
- runtime.GC()
- runtime.GC()
- select {
- case <-done:
- t.Error("ProcThreadAttributeList was garbage collected unexpectedly")
- default:
- }
- list.Delete()
- runtime.GC()
- runtime.GC()
- select {
- case <-done:
- case <-time.After(time.Second):
- t.Error("ProcThreadAttributeList was not garbage collected after a second")
- }
-}
-
func TestPEBFilePath(t *testing.T) {
peb := windows.RtlGetCurrentPeb()
if peb == nil || peb.Ldr == nil {
diff --git a/windows/types_windows.go b/windows/types_windows.go
index 23fe18e..1f73339 100644
--- a/windows/types_windows.go
+++ b/windows/types_windows.go
@@ -909,14 +909,15 @@
// ProcThreadAttributeList is a placeholder type to represent a PROC_THREAD_ATTRIBUTE_LIST.
//
-// To create a *ProcThreadAttributeList, use NewProcThreadAttributeList, and
-// free its memory using ProcThreadAttributeList.Delete.
-type ProcThreadAttributeList struct {
- // This is of type unsafe.Pointer, not of type byte or uintptr, because
- // the contents of it is mostly a list of pointers, and in most cases,
- // that's a list of pointers to Go-allocated objects. In order to keep
- // the GC from collecting these objects, we declare this as unsafe.Pointer.
- _ [1]unsafe.Pointer
+// To create a *ProcThreadAttributeList, use NewProcThreadAttributeList, update
+// it with ProcThreadAttributeListContainer.Update, free its memory using
+// ProcThreadAttributeListContainer.Delete, and access the list itself using
+// ProcThreadAttributeListContainer.List.
+type ProcThreadAttributeList struct{}
+
+type ProcThreadAttributeListContainer struct {
+ data *ProcThreadAttributeList
+ heapAllocations []uintptr
}
type ProcessInformation struct {
