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Lift assumptions from extn.go #151

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merged 5 commits into from
Jan 19, 2023
Merged

Lift assumptions from extn.go #151

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5d56f76
lift some assumptions
jcp19 Jan 17, 2023
76eb626
Merge branch 'master' into joao-extn-non-skippers
jcp19 Jan 18, 2023
c3831ac
Backup
jcp19 Jan 19, 2023
0142797
hopefully done
jcp19 Jan 19, 2023
d2f292e
Merge branch 'master' into joao-extn-non-skippers
jcp19 Jan 19, 2023
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122 changes: 104 additions & 18 deletions pkg/slayers/extn.go
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Original file line number Diff line number Diff line change
Expand Up @@ -98,11 +98,12 @@ func (o *tlvOption) serializeTo(data []byte, fixLengths bool) {
}
}

// @ requires 2 <= len(data)
// @ requires 1 <= len(data)
// @ preserves acc(sl.AbsSlice_Bytes(data, 0, len(data)), def.ReadL20)
// @ ensures err == nil ==> acc(res)
// @ ensures (err == nil && res.OptType != OptTypePad1) ==> (
// @ 2 <= res.ActualLength && res.ActualLength <= len(data) && res.OptData === data[2:res.ActualLength])
// @ ensures err == nil ==> 0 < res.ActualLength
// @ ensures err != nil ==> err.ErrorMem()
// @ decreases
func decodeTLVOption(data []byte) (res *tlvOption, err error) {
Expand Down Expand Up @@ -246,6 +247,7 @@ func (e *extnBase) serializeToWithTLVOptions(b gopacket.SerializeBuffer,
// The following poscondition is more a lot more complicated than it would be if the return type
// was *extnBase instead of extnBase
// @ ensures resErr == nil ==> (
// @ 2 <= len(data) &&
// @ 0 <= res.ActualLen && res.ActualLen <= len(data) &&
// @ res.BaseLayer.Contents === data[:res.ActualLen] &&
// @ res.BaseLayer.Payload === data[res.ActualLen:])
Expand Down Expand Up @@ -296,20 +298,28 @@ func (h *HopByHopExtn) CanDecode() gopacket.LayerClass {
return LayerClassHopByHopExtn
}

// @ trusted
// @ preserves acc(h.Mem(ubuf), def.ReadL20)
// @ decreases
func (h *HopByHopExtn) NextLayerType( /*@ ghost ubuf []byte @*/ ) gopacket.LayerType {
return scionNextLayerTypeAfterHBH(h.NextHdr)
return scionNextLayerTypeAfterHBH( /*@ unfolding acc(h.Mem(ubuf), def.ReadL20) in (unfolding acc(h.extnBase.Mem(ubuf), def.ReadL20) in @*/ h.NextHdr /*@ ) @*/)
}

// @ trusted
// @ requires h.Mem(ub)
// @ ensures sl.AbsSlice_Bytes(res, 0, len(res))
// @ ensures sl.AbsSlice_Bytes(res, 0, len(res)) --* h.Mem(ub)
// @ decreases
func (h *HopByHopExtn) LayerPayload( /*@ ghost ub []byte @*/ ) (res []byte) {
return h.Payload
// @ unfold h.Mem(ub)
// @ unfold h.extnBase.Mem(ub)
// @ ghost base := &h.extnBase.BaseLayer
// @ unfold base.Mem(ub)
tmp := h.Payload
// @ package sl.AbsSlice_Bytes(tmp, 0, len(tmp)) --* h.Mem(ub) {
// @ fold base.Mem(ub)
// @ fold h.extnBase.Mem(ub)
// @ fold h.Mem(ub)
// @ }
return tmp
}

// SerializeTo implementation according to gopacket.SerializableLayer.
Expand All @@ -330,7 +340,6 @@ func (h *HopByHopExtn) SerializeTo(b gopacket.SerializeBuffer,
}

// DecodeFromBytes implementation according to gopacket.DecodingLayer.
// @ trusted
// @ requires sl.AbsSlice_Bytes(data, 0, len(data))
// @ requires h.NonInitMem()
// @ requires df != nil
Expand All @@ -341,36 +350,74 @@ func (h *HopByHopExtn) SerializeTo(b gopacket.SerializeBuffer,
// @ decreases
func (h *HopByHopExtn) DecodeFromBytes(data []byte, df gopacket.DecodeFeedback) (res error) {
var err error
// @ unfold h.NonInitMem()
h.Options = nil
h.extnBase, err = decodeExtnBase(data, df)
if err != nil {
// @ fold h.NonInitMem()
return err
}
if err := checkHopByHopExtnNextHdr(h.NextHdr); err != nil {
// @ fold h.NonInitMem()
return err
}
offset := 2

// @ ghost lenOptions := 0

// @ invariant 2 <= offset
// @ invariant acc(h)
// @ invariant 0 <= h.ActualLen && h.ActualLen <= len(data)
// @ invariant len(h.Options) == lenOptions
// @ invariant forall i int :: { &h.Options[i] } 0 <= i && i < lenOptions ==>
// @ (acc(&h.Options[i]) && h.Options[i].Mem(i))
// @ invariant sl.AbsSlice_Bytes(data, 0, len(data))
// framing:
// @ invariant h.BaseLayer.Contents === data[:h.ActualLen]
// @ invariant h.BaseLayer.Payload === data[h.ActualLen:]
// @ decreases h.ActualLen - offset
for offset < h.ActualLen {
// @ sl.SplitRange_Bytes(data, offset, h.ActualLen, def.ReadL20)
opt, err := decodeTLVOption(data[offset:h.ActualLen])
// @ sl.CombineRange_Bytes(data, offset, h.ActualLen, def.ReadL20)
if err != nil {
// @ fold h.NonInitMem()
return err
}
h.Options = append(h.Options, (*HopByHopOption)(opt))
// @ ghost tmp := (*HopByHopOption)(opt)
h.Options = append( /*@ perm(1/2), @*/ h.Options, (*HopByHopOption)(opt))
offset += opt.ActualLength
}
// @ assert h.Options[lenOptions] === tmp
// @ fold tmp.Mem(lenOptions)
// @ lenOptions += 1
}
// @ sl.SplitByIndex_Bytes(data, 0, len(data), h.ActualLen, writePerm)
// @ sl.Reslice_Bytes(data, 0, h.ActualLen, writePerm)
// @ sl.Reslice_Bytes(data, h.ActualLen, len(data), writePerm)
// @ fold h.extnBase.BaseLayer.Mem(data)
// @ fold h.extnBase.Mem(data)
// @ fold h.Mem(data)
return nil
}

// (VerifiedSCION) TODO: to be handled when the initialization of slayers is handled in
// layertypes.go.
// @ trusted
// @ requires false
func decodeHopByHopExtn(data []byte, p gopacket.PacketBuilder) error {
// @ requires false
// @ requires sl.AbsSlice_Bytes(data, 0, len(data))
// @ requires p != nil
// @ preserves p.Mem()
// @ ensures res != nil ==> res.ErrorMem()
// @ decreases
func decodeHopByHopExtn(data []byte, p gopacket.PacketBuilder) (res error) {
h := &HopByHopExtn{}
// @ fold h.NonInitMem()
err := h.DecodeFromBytes(data, p)
p.AddLayer(h)
if err != nil {
return err
}
return p.NextDecoder(scionNextLayerTypeAfterHBH(h.NextHdr))
return p.NextDecoder(scionNextLayerTypeAfterHBH(( /*@ unfolding h.Mem(data) in (unfolding h.extnBase.Mem(data) in @*/ h.NextHdr /*@ ) @*/)))
}

// @ ensures (t == HopByHopClass) == (err != nil)
Expand Down Expand Up @@ -403,24 +450,31 @@ func (e *EndToEndExtn) CanDecode() gopacket.LayerClass {
return LayerClassEndToEndExtn
}

// @ trusted
// @ preserves acc(e.Mem(ubuf), def.ReadL20)
// @ decreases
func (e *EndToEndExtn) NextLayerType( /*@ ghost ubuf []byte @*/ ) gopacket.LayerType {
return scionNextLayerTypeAfterE2E(e.NextHdr)
return scionNextLayerTypeAfterE2E( /*@ unfolding acc(e.Mem(ubuf), def.ReadL20) in (unfolding acc(e.extnBase.Mem(ubuf), def.ReadL20) in @*/ e.NextHdr /*@ ) @*/)
}

// @ trusted
// @ requires e.Mem(ub)
// @ ensures sl.AbsSlice_Bytes(res, 0, len(res))
// @ ensures sl.AbsSlice_Bytes(res, 0, len(res)) --* e.Mem(ub)
// @ decreases
func (e *EndToEndExtn) LayerPayload( /*@ ghost ub []byte @*/ ) (res []byte) {
return e.Payload
// @ unfold e.Mem(ub)
// @ unfold e.extnBase.Mem(ub)
// @ ghost base := &e.extnBase.BaseLayer
// @ unfold base.Mem(ub)
tmp := e.Payload
// @ package sl.AbsSlice_Bytes(tmp, 0, len(tmp)) --* e.Mem(ub) {
// @ fold base.Mem(ub)
// @ fold e.extnBase.Mem(ub)
// @ fold e.Mem(ub)
// @ }
return tmp
}

// DecodeFromBytes implementation according to gopacket.DecodingLayer.
// @ trusted
// @ requires sl.AbsSlice_Bytes(data, 0, len(data))
// @ requires e.NonInitMem()
// @ requires df != nil
Expand All @@ -431,26 +485,58 @@ func (e *EndToEndExtn) LayerPayload( /*@ ghost ub []byte @*/ ) (res []byte) {
// @ decreases
func (e *EndToEndExtn) DecodeFromBytes(data []byte, df gopacket.DecodeFeedback) (res error) {
var err error
// @ unfold e.NonInitMem()
e.Options = nil
e.extnBase, err = decodeExtnBase(data, df)
if err != nil {
// @ fold e.NonInitMem()
return err
}
if err := checkEndToEndExtnNextHdr(e.NextHdr); err != nil {
// @ fold e.NonInitMem()
return err
}
offset := 2

// @ ghost lenOptions := 0

// @ invariant 2 <= offset
// @ invariant acc(e)
// @ invariant 0 <= e.ActualLen && e.ActualLen <= len(data)
// @ invariant len(e.Options) == lenOptions
// @ invariant forall i int :: { &e.Options[i] } 0 <= i && i < lenOptions ==>
// @ (acc(&e.Options[i]) && e.Options[i].Mem(i))
// @ invariant sl.AbsSlice_Bytes(data, 0, len(data))
// framing:
// @ invariant e.BaseLayer.Contents === data[:e.ActualLen]
// @ invariant e.BaseLayer.Payload === data[e.ActualLen:]
// @ decreases e.ActualLen - offset
for offset < e.ActualLen {
// @ sl.SplitRange_Bytes(data, offset, e.ActualLen, def.ReadL20)
opt, err := decodeTLVOption(data[offset:e.ActualLen])
// @ sl.CombineRange_Bytes(data, offset, e.ActualLen, def.ReadL20)
if err != nil {
// @ fold e.NonInitMem()
return err
}
e.Options = append(e.Options, (*EndToEndOption)(opt))
// @ ghost tmp := (*EndToEndOption)(opt)
e.Options = append( /*@ perm(1/2), @*/ e.Options, (*EndToEndOption)(opt))
offset += opt.ActualLength
}
// @ assert e.Options[lenOptions] === tmp
// @ fold tmp.Mem(lenOptions)
// @ lenOptions += 1
}
// @ sl.SplitByIndex_Bytes(data, 0, len(data), e.ActualLen, writePerm)
// @ sl.Reslice_Bytes(data, 0, e.ActualLen, writePerm)
// @ sl.Reslice_Bytes(data, e.ActualLen, len(data), writePerm)
// @ fold e.extnBase.BaseLayer.Mem(data)
// @ fold e.extnBase.Mem(data)
// @ fold e.Mem(data)
return nil
}

// (VerifiedSCION) TODO: to be handled when the initialization of slayers is handled in
// layertypes.go.
// @ trusted
// @ requires false
func decodeEndToEndExtn(data []byte, p gopacket.PacketBuilder) error {
Expand Down
26 changes: 22 additions & 4 deletions pkg/slayers/extn_spec.gobra
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Original file line number Diff line number Diff line change
Expand Up @@ -47,7 +47,7 @@ pred (h *HopByHopExtn) Mem(ubuf []byte) {
h.extnBase.Mem(ubuf) &&
acc(&h.Options) &&
forall i int :: { &h.Options[i] } 0 <= i && i < len(h.Options) ==>
(acc(&h.Options[i]) && h.Options[i].Mem())
(acc(&h.Options[i]) && h.Options[i].Mem(i))
}

// Gobra is not able to infer that HopByHopExtn is "inheriting"
Expand Down Expand Up @@ -105,9 +105,16 @@ func (h *HopByHopExtnSkipper) LayerPayload(ghost ub []byte) (res []byte) {
/** end of HopByHopExtnSkipper **/

/** Currently Axiomatized - EndToEndExtn **/
pred (e *EndToEndExtn) NonInitMem()
pred (e *EndToEndExtn) NonInitMem() {
acc(e)
}

pred (e *EndToEndExtn) Mem(ubuf []byte)
pred (e *EndToEndExtn) Mem(ubuf []byte) {
e.extnBase.Mem(ubuf) &&
acc(&e.Options) &&
forall i int :: { &e.Options[i] } 0 <= i && i < len(e.Options) ==>
(acc(&e.Options[i]) && e.Options[i].Mem(i))
}

// Gobra is not able to infer that EndToEndExtn is "inheriting"
// the implementation of LayerContents from extnBase.
Expand Down Expand Up @@ -191,10 +198,21 @@ pure func computeLen(options []*tlvOption, start, end int) (res int) {

/** start of options **/

pred (o *HopByHopOption) Mem() {
// TODO: maybe add the underlying slice as a parameter to be able to
// establish that OptData aliases with it.
pred (o *HopByHopOption) Mem(_ int) {
// permissions to the elements of OptData will be stored
// together with the underlying, not in the option itself
acc(o) // && slices.AbsSlice_Bytes(o.OptData, 0, len(o.OptData))
}

// TODO: maybe add the underlying slice as a parameter to be able to
// establish that OptData aliases with it.
pred (e *EndToEndOption) Mem(_ int) {
// permissions to the elements of OptData will be stored
// together with the underlying, not in the option itself
acc(e) // && slices.AbsSlice_Bytes(e.OptData, 0, len(e.OptData))
}


/** end of options **/