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// Copyright 2018 The gVisor Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package arch
import (
"encoding/binary"
"fmt"
"gvisor.dev/gvisor/pkg/context"
"gvisor.dev/gvisor/pkg/usermem"
)
// Stack is a simple wrapper around a usermem.IO and an address.
type Stack struct {
// Our arch info.
// We use this for automatic Native conversion of usermem.Addrs during
// Push() and Pop().
Arch Context
// The interface used to actually copy user memory.
IO usermem.IO
// Our current stack bottom.
Bottom usermem.Addr
}
// Push pushes the given values on to the stack.
//
// (This method supports Addrs and treats them as native types.)
func (s *Stack) Push(vals ...interface{}) (usermem.Addr, error) {
for _, v := range vals {
// We convert some types to well-known serializable quanities.
var norm interface{}
// For array types, we will automatically add an appropriate
// terminal value. This is done simply to make the interface
// easier to use.
var term interface{}
switch v.(type) {
case string:
norm = []byte(v.(string))
term = byte(0)
case []int8, []uint8:
norm = v
term = byte(0)
case []int16, []uint16:
norm = v
term = uint16(0)
case []int32, []uint32:
norm = v
term = uint32(0)
case []int64, []uint64:
norm = v
term = uint64(0)
case []usermem.Addr:
// Special case: simply push recursively.
_, err := s.Push(s.Arch.Native(uintptr(0)))
if err != nil {
return 0, err
}
varr := v.([]usermem.Addr)
for i := len(varr) - 1; i >= 0; i-- {
_, err := s.Push(varr[i])
if err != nil {
return 0, err
}
}
continue
case usermem.Addr:
norm = s.Arch.Native(uintptr(v.(usermem.Addr)))
default:
norm = v
}
if term != nil {
_, err := s.Push(term)
if err != nil {
return 0, err
}
}
c := binary.Size(norm)
if c < 0 {
return 0, fmt.Errorf("bad binary.Size for %T", v)
}
// TODO(b/38173783): Use a real context.Context.
n, err := usermem.CopyObjectOut(context.Background(), s.IO, s.Bottom-usermem.Addr(c), norm, usermem.IOOpts{})
if err != nil || c != n {
return 0, err
}
s.Bottom -= usermem.Addr(n)
}
return s.Bottom, nil
}
// Pop pops the given values off the stack.
//
// (This method supports Addrs and treats them as native types.)
func (s *Stack) Pop(vals ...interface{}) (usermem.Addr, error) {
for _, v := range vals {
vaddr, isVaddr := v.(*usermem.Addr)
var n int
var err error
if isVaddr {
value := s.Arch.Native(uintptr(0))
// TODO(b/38173783): Use a real context.Context.
n, err = usermem.CopyObjectIn(context.Background(), s.IO, s.Bottom, value, usermem.IOOpts{})
*vaddr = usermem.Addr(s.Arch.Value(value))
} else {
// TODO(b/38173783): Use a real context.Context.
n, err = usermem.CopyObjectIn(context.Background(), s.IO, s.Bottom, v, usermem.IOOpts{})
}
if err != nil {
return 0, err
}
s.Bottom += usermem.Addr(n)
}
return s.Bottom, nil
}
// Align aligns the stack to the given offset.
func (s *Stack) Align(offset int) {
if s.Bottom%usermem.Addr(offset) != 0 {
s.Bottom -= (s.Bottom % usermem.Addr(offset))
}
}
// StackLayout describes the location of the arguments and environment on the
// stack.
type StackLayout struct {
// ArgvStart is the beginning of the argument vector.
ArgvStart usermem.Addr
// ArgvEnd is the end of the argument vector.
ArgvEnd usermem.Addr
// EnvvStart is the beginning of the environment vector.
EnvvStart usermem.Addr
// EnvvEnd is the end of the environment vector.
EnvvEnd usermem.Addr
}
// Load pushes the given args, env and aux vector to the stack using the
// well-known format for a new executable. It returns the start and end
// of the argument and environment vectors.
func (s *Stack) Load(args []string, env []string, aux Auxv) (StackLayout, error) {
l := StackLayout{}
// Make sure we start with a 16-byte alignment.
s.Align(16)
// Push the environment vector so the end of the argument vector is adjacent to
// the beginning of the environment vector.
// While the System V abi for x86_64 does not specify an ordering to the
// Information Block (the block holding the arg, env, and aux vectors),
// support features like setproctitle(3) naturally expect these segments
// to be in this order. See: https://www.uclibc.org/docs/psABI-x86_64.pdf
// page 29.
l.EnvvEnd = s.Bottom
envAddrs := make([]usermem.Addr, len(env))
for i := len(env) - 1; i >= 0; i-- {
addr, err := s.Push(env[i])
if err != nil {
return StackLayout{}, err
}
envAddrs[i] = addr
}
l.EnvvStart = s.Bottom
// Push our strings.
l.ArgvEnd = s.Bottom
argAddrs := make([]usermem.Addr, len(args))
for i := len(args) - 1; i >= 0; i-- {
addr, err := s.Push(args[i])
if err != nil {
return StackLayout{}, err
}
argAddrs[i] = addr
}
l.ArgvStart = s.Bottom
// We need to align the arguments appropriately.
//
// We must finish on a 16-byte alignment, but we'll play it
// conservatively and finish at 32-bytes. It would be nice to be able
// to call Align here, but unfortunately we need to align the stack
// with all the variable sized arrays pushed. So we just need to do
// some calculations.
argvSize := s.Arch.Width() * uint(len(args)+1)
envvSize := s.Arch.Width() * uint(len(env)+1)
auxvSize := s.Arch.Width() * 2 * uint(len(aux)+1)
total := usermem.Addr(argvSize) + usermem.Addr(envvSize) + usermem.Addr(auxvSize) + usermem.Addr(s.Arch.Width())
expectedBottom := s.Bottom - total
if expectedBottom%32 != 0 {
s.Bottom -= expectedBottom % 32
}
// Push our auxvec.
// NOTE: We need an extra zero here per spec.
// The Push function will automatically terminate
// strings and arrays with a single null value.
auxv := make([]usermem.Addr, 0, len(aux))
for _, a := range aux {
auxv = append(auxv, usermem.Addr(a.Key), a.Value)
}
auxv = append(auxv, usermem.Addr(0))
_, err := s.Push(auxv)
if err != nil {
return StackLayout{}, err
}
// Push environment.
_, err = s.Push(envAddrs)
if err != nil {
return StackLayout{}, err
}
// Push args.
_, err = s.Push(argAddrs)
if err != nil {
return StackLayout{}, err
}
// Push arg count.
_, err = s.Push(usermem.Addr(len(args)))
if err != nil {
return StackLayout{}, err
}
return l, nil
}
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