libgo/go/runtime/checkptr.go

   1 // Copyright 2019 The Go Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style
   3 // license that can be found in the LICENSE file.
   4
   5 //go:build ignore
   6 // +build ignore
   7
   8 package runtime
   9
  10 import "unsafe"
  11
  12 func checkptrAlignment(p unsafe.Pointer, elem *_type, n uintptr) {
  13         // nil pointer is always suitably aligned (#47430).
  14         if p == nil {
  15                 return
  16         }
  17
  18         // Check that (*[n]elem)(p) is appropriately aligned.
  19         // Note that we allow unaligned pointers if the types they point to contain
  20         // no pointers themselves. See issue 37298.
  21         // TODO(mdempsky): What about fieldAlign?
  22         if elem.ptrdata != 0 && uintptr(p)&(uintptr(elem.align)-1) != 0 {
  23                 throw("checkptr: misaligned pointer conversion")
  24         }
  25
  26         // Check that (*[n]elem)(p) doesn't straddle multiple heap objects.
  27         // TODO(mdempsky): Fix #46938 so we don't need to worry about overflow here.
  28         if checkptrStraddles(p, n*elem.size) {
  29                 throw("checkptr: converted pointer straddles multiple allocations")
  30         }
  31 }
  32
  33 // checkptrStraddles reports whether the first size-bytes of memory
  34 // addressed by ptr is known to straddle more than one Go allocation.
  35 func checkptrStraddles(ptr unsafe.Pointer, size uintptr) bool {
  36         if size <= 1 {
  37                 return false
  38         }
  39
  40         // Check that add(ptr, size-1) won't overflow. This avoids the risk
  41         // of producing an illegal pointer value (assuming ptr is legal).
  42         if uintptr(ptr) >= -(size - 1) {
  43                 return true
  44         }
  45         end := add(ptr, size-1)
  46
  47         // TODO(mdempsky): Detect when [ptr, end] contains Go allocations,
  48         // but neither ptr nor end point into one themselves.
  49
  50         return checkptrBase(ptr) != checkptrBase(end)
  51 }
  52
  53 func checkptrArithmetic(p unsafe.Pointer, originals []unsafe.Pointer) {
  54         if 0 < uintptr(p) && uintptr(p) < minLegalPointer {
  55                 throw("checkptr: pointer arithmetic computed bad pointer value")
  56         }
  57
  58         // Check that if the computed pointer p points into a heap
  59         // object, then one of the original pointers must have pointed
  60         // into the same object.
  61         base := checkptrBase(p)
  62         if base == 0 {
  63                 return
  64         }
  65
  66         for _, original := range originals {
  67                 if base == checkptrBase(original) {
  68                         return
  69                 }
  70         }
  71
  72         throw("checkptr: pointer arithmetic result points to invalid allocation")
  73 }
  74
  75 // checkptrBase returns the base address for the allocation containing
  76 // the address p.
  77 //
  78 // Importantly, if p1 and p2 point into the same variable, then
  79 // checkptrBase(p1) == checkptrBase(p2). However, the converse/inverse
  80 // is not necessarily true as allocations can have trailing padding,
  81 // and multiple variables may be packed into a single allocation.
  82 func checkptrBase(p unsafe.Pointer) uintptr {
  83         // stack
  84         if gp := getg(); gp.stack.lo <= uintptr(p) && uintptr(p) < gp.stack.hi {
  85                 // TODO(mdempsky): Walk the stack to identify the
  86                 // specific stack frame or even stack object that p
  87                 // points into.
  88                 //
  89                 // In the mean time, use "1" as a pseudo-address to
  90                 // represent the stack. This is an invalid address on
  91                 // all platforms, so it's guaranteed to be distinct
  92                 // from any of the addresses we might return below.
  93                 return 1
  94         }
  95
  96         // heap (must check after stack because of #35068)
  97         if base, _, _ := findObject(uintptr(p), 0, 0); base != 0 {
  98                 return base
  99         }
 100
 101         // data or bss
 102         for _, datap := range activeModules() {
 103                 if datap.data <= uintptr(p) && uintptr(p) < datap.edata {
 104                         return datap.data
 105                 }
 106                 if datap.bss <= uintptr(p) && uintptr(p) < datap.ebss {
 107                         return datap.bss
 108                 }
 109         }
 110
 111         return 0
 112 }