// Copyright 2009 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. // Cgo call and callback support. package runtime import ( "runtime/internal/sys" "unsafe" ) // Functions called by cgo-generated code. //go:linkname cgoCheckPointer //go:linkname cgoCheckResult // Pointer checking for cgo code. // We want to detect all cases where a program that does not use // unsafe makes a cgo call passing a Go pointer to memory that // contains a Go pointer. Here a Go pointer is defined as a pointer // to memory allocated by the Go runtime. Programs that use unsafe // can evade this restriction easily, so we don't try to catch them. // The cgo program will rewrite all possibly bad pointer arguments to // call cgoCheckPointer, where we can catch cases of a Go pointer // pointing to a Go pointer. // Complicating matters, taking the address of a slice or array // element permits the C program to access all elements of the slice // or array. In that case we will see a pointer to a single element, // but we need to check the entire data structure. // The cgoCheckPointer call takes additional arguments indicating that // it was called on an address expression. An additional argument of // true means that it only needs to check a single element. An // additional argument of a slice or array means that it needs to // check the entire slice/array, but nothing else. Otherwise, the // pointer could be anything, and we check the entire heap object, // which is conservative but safe. // When and if we implement a moving garbage collector, // cgoCheckPointer will pin the pointer for the duration of the cgo // call. (This is necessary but not sufficient; the cgo program will // also have to change to pin Go pointers that cannot point to Go // pointers.) // cgoCheckPointer checks if the argument contains a Go pointer that // points to a Go pointer, and panics if it does. func cgoCheckPointer(ptr interface{}, args ...interface{}) { if debug.cgocheck == 0 { return } ep := (*eface)(unsafe.Pointer(&ptr)) t := ep._type top := true if len(args) > 0 && (t.kind&kindMask == kindPtr || t.kind&kindMask == kindUnsafePointer) { p := ep.data if t.kind&kindDirectIface == 0 { p = *(*unsafe.Pointer)(p) } if !cgoIsGoPointer(p) { return } aep := (*eface)(unsafe.Pointer(&args[0])) switch aep._type.kind & kindMask { case kindBool: if t.kind&kindMask == kindUnsafePointer { // We don't know the type of the element. break } pt := (*ptrtype)(unsafe.Pointer(t)) cgoCheckArg(pt.elem, p, true, false, cgoCheckPointerFail) return case kindSlice: // Check the slice rather than the pointer. ep = aep t = ep._type case kindArray: // Check the array rather than the pointer. // Pass top as false since we have a pointer // to the array. ep = aep t = ep._type top = false default: throw("can't happen") } } cgoCheckArg(t, ep.data, t.kind&kindDirectIface == 0, top, cgoCheckPointerFail) } const cgoCheckPointerFail = "cgo argument has Go pointer to Go pointer" const cgoResultFail = "cgo result has Go pointer" // cgoCheckArg is the real work of cgoCheckPointer. The argument p // is either a pointer to the value (of type t), or the value itself, // depending on indir. The top parameter is whether we are at the top // level, where Go pointers are allowed. func cgoCheckArg(t *_type, p unsafe.Pointer, indir, top bool, msg string) { if t.ptrdata == 0 { // If the type has no pointers there is nothing to do. return } switch t.kind & kindMask { default: throw("can't happen") case kindArray: at := (*arraytype)(unsafe.Pointer(t)) if !indir { if at.len != 1 { throw("can't happen") } cgoCheckArg(at.elem, p, at.elem.kind&kindDirectIface == 0, top, msg) return } for i := uintptr(0); i < at.len; i++ { cgoCheckArg(at.elem, p, true, top, msg) p = add(p, at.elem.size) } case kindChan, kindMap: // These types contain internal pointers that will // always be allocated in the Go heap. It's never OK // to pass them to C. panic(errorString(msg)) case kindFunc: if indir { p = *(*unsafe.Pointer)(p) } if !cgoIsGoPointer(p) { return } panic(errorString(msg)) case kindInterface: it := *(**_type)(p) if it == nil { return } // A type known at compile time is OK since it's // constant. A type not known at compile time will be // in the heap and will not be OK. if inheap(uintptr(unsafe.Pointer(it))) { panic(errorString(msg)) } p = *(*unsafe.Pointer)(add(p, sys.PtrSize)) if !cgoIsGoPointer(p) { return } if !top { panic(errorString(msg)) } cgoCheckArg(it, p, it.kind&kindDirectIface == 0, false, msg) case kindSlice: st := (*slicetype)(unsafe.Pointer(t)) s := (*slice)(p) p = s.array if !cgoIsGoPointer(p) { return } if !top { panic(errorString(msg)) } if st.elem.ptrdata == 0 { return } for i := 0; i < s.cap; i++ { cgoCheckArg(st.elem, p, true, false, msg) p = add(p, st.elem.size) } case kindString: ss := (*stringStruct)(p) if !cgoIsGoPointer(ss.str) { return } if !top { panic(errorString(msg)) } case kindStruct: st := (*structtype)(unsafe.Pointer(t)) if !indir { if len(st.fields) != 1 { throw("can't happen") } cgoCheckArg(st.fields[0].typ, p, st.fields[0].typ.kind&kindDirectIface == 0, top, msg) return } for _, f := range st.fields { cgoCheckArg(f.typ, add(p, f.offset()), true, top, msg) } case kindPtr, kindUnsafePointer: if indir { p = *(*unsafe.Pointer)(p) } if !cgoIsGoPointer(p) { return } if !top { panic(errorString(msg)) } cgoCheckUnknownPointer(p, msg) } } // cgoCheckUnknownPointer is called for an arbitrary pointer into Go // memory. It checks whether that Go memory contains any other // pointer into Go memory. If it does, we panic. // The return values are unused but useful to see in panic tracebacks. func cgoCheckUnknownPointer(p unsafe.Pointer, msg string) (base, i uintptr) { if inheap(uintptr(p)) { b, span, _ := findObject(uintptr(p), 0, 0, false) base = b if base == 0 { return } hbits := heapBitsForAddr(base) n := span.elemsize for i = uintptr(0); i < n; i += sys.PtrSize { if i != 1*sys.PtrSize && !hbits.morePointers() { // No more possible pointers. break } if hbits.isPointer() && cgoIsGoPointer(*(*unsafe.Pointer)(unsafe.Pointer(base + i))) { panic(errorString(msg)) } hbits = hbits.next() } return } lo := 0 hi := len(gcRootsIndex) for lo < hi { m := lo + (hi-lo)/2 pr := gcRootsIndex[m] addr := uintptr(pr.decl) if cgoInRange(p, addr, addr+pr.size) { cgoCheckBits(pr.decl, pr.gcdata, 0, pr.ptrdata) return } if uintptr(p) < addr { hi = m } else { lo = m + 1 } } return } // cgoIsGoPointer reports whether the pointer is a Go pointer--a // pointer to Go memory. We only care about Go memory that might // contain pointers. //go:nosplit //go:nowritebarrierrec func cgoIsGoPointer(p unsafe.Pointer) bool { if p == nil { return false } if inHeapOrStack(uintptr(p)) { return true } roots := gcRoots for roots != nil { for i := 0; i < roots.count; i++ { pr := roots.roots[i] addr := uintptr(pr.decl) if cgoInRange(p, addr, addr+pr.size) { return true } } roots = roots.next } return false } // cgoInRange reports whether p is between start and end. //go:nosplit //go:nowritebarrierrec func cgoInRange(p unsafe.Pointer, start, end uintptr) bool { return start <= uintptr(p) && uintptr(p) < end } // cgoCheckResult is called to check the result parameter of an // exported Go function. It panics if the result is or contains a Go // pointer. func cgoCheckResult(val interface{}) { if debug.cgocheck == 0 { return } ep := (*eface)(unsafe.Pointer(&val)) t := ep._type cgoCheckArg(t, ep.data, t.kind&kindDirectIface == 0, false, cgoResultFail) }