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Use a random subset of syscalls/corpus/coverage for each individual VM run. Hypothesis is that this should allow fuzzer to get more coverage find more bugs in saturated state (stuck in local optimum). See the issue and comments for details. Update #1348
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,240 @@ | ||
| // Copyright 2019 syzkaller project authors. All rights reserved. | ||
| // Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file. | ||
|
|
||
| package prog | ||
|
|
||
| import ( | ||
| "math/rand" | ||
| "sort" | ||
| ) | ||
|
|
||
| // Rotator selects a random subset of syscalls for corpus rotation. | ||
| type Rotator struct { | ||
| target *Target | ||
| calls map[*Syscall]bool | ||
| rnd *rand.Rand | ||
| resourceless []*Syscall | ||
| syscallUses map[*Syscall][]*ResourceDesc | ||
| resources map[*ResourceDesc]rotatorResource | ||
| goal int | ||
| nresourceless int | ||
| } | ||
|
|
||
| type rotatorResource struct { | ||
| // 0 - precise ctors that don't require other resources as inputs (e.g. socket). | ||
| // 1 - precise ctors that require other resources (e.g. accept). | ||
| // 2 - all imprecise ctors. | ||
| ctors [3][]*Syscall | ||
| // 0 - precise uses of this resource. | ||
| // 1 - uses of parent resources (e.g. close for sock). | ||
| uses [2][]*Syscall | ||
| } | ||
|
|
||
| func MakeRotator(target *Target, calls map[*Syscall]bool, rnd *rand.Rand) *Rotator { | ||
| r := &Rotator{ | ||
| target: target, | ||
| calls: calls, | ||
| rnd: rnd, | ||
| syscallUses: make(map[*Syscall][]*ResourceDesc), | ||
| resources: make(map[*ResourceDesc]rotatorResource), | ||
| } | ||
| for call := range calls { | ||
| r.syscallUses[call] = append(r.syscallUses[call], call.inputResources...) | ||
| r.syscallUses[call] = append(r.syscallUses[call], call.outputResources...) | ||
| var inputs []*ResourceDesc | ||
| for _, res := range call.inputResources { | ||
| // Don't take into account pid/uid/etc, they create too many links. | ||
| if !target.AuxResources[res.Name] { | ||
| inputs = append(inputs, res) | ||
| } | ||
| } | ||
| // VMAs and filenames are effectively resources for our purposes | ||
| // (but they don't have ctors). | ||
| ForeachType(call, func(t Type) { | ||
| switch a := t.(type) { | ||
| case *BufferType: | ||
| switch a.Kind { | ||
| case BufferFilename: | ||
| inputs = append(inputs, filenameRes) | ||
| } | ||
| case *VmaType: | ||
| inputs = append(inputs, vmaRes) | ||
| } | ||
| }) | ||
|
|
||
| inputDedup := make(map[string]bool, len(inputs)) | ||
| for _, res := range inputs { | ||
| if inputDedup[res.Name] { | ||
| continue | ||
| } | ||
| inputDedup[res.Name] = true | ||
| info := r.resources[res] | ||
| info.uses[0] = append(info.uses[0], call) | ||
| r.resources[res] = info | ||
|
|
||
| for _, kind := range res.Kind[:len(res.Kind)-1] { | ||
| parent := target.resourceMap[kind] | ||
| info := r.resources[parent] | ||
| info.uses[1] = append(info.uses[1], call) | ||
| r.resources[parent] = info | ||
| } | ||
| } | ||
| outputDedup := make(map[string]bool, len(call.outputResources)) | ||
| for _, res := range call.outputResources { | ||
| if outputDedup[res.Name] { | ||
| continue | ||
| } | ||
| outputDedup[res.Name] = true | ||
| info := r.resources[res] | ||
| class := 0 | ||
| if len(inputs) != 0 { | ||
| class = 1 | ||
| } | ||
| info.ctors[class] = append(info.ctors[class], call) | ||
| r.resources[res] = info | ||
| for _, kind := range res.Kind[:len(res.Kind)-1] { | ||
| parent := target.resourceMap[kind] | ||
| info := r.resources[parent] | ||
| info.ctors[2] = append(info.ctors[2], call) | ||
| r.resources[parent] = info | ||
| } | ||
| } | ||
| if len(inputs)+len(call.outputResources) == 0 { | ||
| r.resourceless = append(r.resourceless, call) | ||
| } | ||
| } | ||
| // For smaller syscall sets we drop ~5% of syscalls. | ||
| // However, we assume that 200 syscalls is enough for a fuzzing session, | ||
| // so we cap at that level to make fuzzing more targeted. | ||
| r.goal = len(calls) * 19 / 20 | ||
| if r.goal < 1 { | ||
| r.goal = 1 | ||
| } | ||
| if max := 200; r.goal > max { | ||
| r.goal = max | ||
| } | ||
| // How many syscalls that don't use any resources we want to add? | ||
| r.nresourceless = r.goal * len(r.resourceless) / len(calls) | ||
| if r.nresourceless < 1 { | ||
| r.nresourceless = 1 | ||
| } | ||
| return r | ||
| } | ||
|
|
||
| func (r *Rotator) Select() map[*Syscall]bool { | ||
| rs := rotatorState{ | ||
| Rotator: r, | ||
| calls: make(map[*Syscall]bool, 3*r.goal), | ||
| } | ||
| return rs.Select() | ||
| } | ||
|
|
||
| type rotatorState struct { | ||
| *Rotator | ||
| calls map[*Syscall]bool | ||
| topQueue []*ResourceDesc | ||
| depQueue []*ResourceDesc | ||
| topHandled map[*ResourceDesc]bool | ||
| depHandled map[*ResourceDesc]bool | ||
| } | ||
|
|
||
| func (rs *rotatorState) Select() map[*Syscall]bool { | ||
| // The algorithm is centered around resources. | ||
| // But first we add some syscalls that don't use any resources at all | ||
| // Otherwise we will never add them in the loop. | ||
| // Then, we select a resource and add some ctors for this resources | ||
| // and some calls that use it. That's handled by topQueue. | ||
| // If any of the calls require other resources as inputs, we also add | ||
| // some ctors for these resources, but don't add calls that use them. | ||
| // That's handled by depQueue. | ||
| // However, a resource can be handled as dependency first, but then | ||
| // handled as top resource again. In such case we will still add calls | ||
| // that use this resource. | ||
| for { | ||
| if len(rs.depQueue) == 0 && len(rs.calls) >= rs.goal || len(rs.calls) >= 2*rs.goal { | ||
| rs.calls, _ = rs.target.transitivelyEnabled(rs.calls) | ||
| if len(rs.calls) >= rs.goal { | ||
| return rs.calls | ||
| } | ||
| } | ||
| if len(rs.depQueue) != 0 { | ||
| // Handle a dependent resource, add only ctors for these. | ||
| // Pick a random one, this gives a mix of DFS and BFS. | ||
| idx := rs.rnd.Intn(len(rs.depQueue)) | ||
| res := rs.depQueue[idx] | ||
| rs.depQueue[idx] = rs.depQueue[len(rs.depQueue)-1] | ||
| rs.depQueue = rs.depQueue[:len(rs.depQueue)-1] | ||
| info := rs.resources[res] | ||
| nctors0 := len(info.ctors[0]) != 0 | ||
| nctors1 := nctors0 || len(info.ctors[1]) != 0 | ||
| rs.selectCalls(info.ctors[0], 2, true) | ||
| if nctors0 { | ||
| continue | ||
| } | ||
| rs.selectCalls(info.ctors[1], 2, !nctors0) | ||
| if nctors1 { | ||
| continue | ||
| } | ||
| rs.selectCalls(info.ctors[0], 2, !nctors1) | ||
| continue | ||
| } | ||
| if len(rs.topQueue) == 0 { | ||
| // We either just started selection or we handled all resources, | ||
| // but did not gather enough syscalls. In both cases we need | ||
| // to reset all queues. | ||
| rs.topQueue = make([]*ResourceDesc, 0, len(rs.resources)) | ||
| rs.depQueue = make([]*ResourceDesc, 0, len(rs.resources)) | ||
| rs.topHandled = make(map[*ResourceDesc]bool, len(rs.resources)) | ||
| rs.depHandled = make(map[*ResourceDesc]bool, len(rs.resources)) | ||
| for res := range rs.resources { | ||
| rs.topQueue = append(rs.topQueue, res) | ||
| } | ||
| sort.Slice(rs.topQueue, func(i, j int) bool { | ||
| return rs.topQueue[i].Name < rs.topQueue[j].Name | ||
| }) | ||
| rs.rnd.Shuffle(len(rs.topQueue), func(i, j int) { | ||
| rs.topQueue[i], rs.topQueue[j] = rs.topQueue[j], rs.topQueue[i] | ||
| }) | ||
| rs.selectCalls(rs.resourceless, rs.nresourceless+1, false) | ||
| } | ||
| // Handle a top resource, add more syscalls for these. | ||
| res := rs.topQueue[0] | ||
| rs.topQueue = rs.topQueue[1:] | ||
| if rs.topHandled[res] { | ||
| panic("top queue already handled") | ||
| } | ||
| rs.topHandled[res] = true | ||
| info := rs.resources[res] | ||
| nctors0 := len(info.ctors[0]) != 0 | ||
| nctors1 := nctors0 || len(info.ctors[1]) != 0 | ||
| rs.selectCalls(info.ctors[0], 5, true) | ||
| rs.selectCalls(info.ctors[1], 3, !nctors0) | ||
| rs.selectCalls(info.ctors[0], 2, !nctors1) | ||
| rs.selectCalls(info.uses[0], 20, true) | ||
| rs.selectCalls(info.uses[1], 2, len(info.uses[0]) == 0) | ||
| } | ||
| } | ||
|
|
||
| func (rs *rotatorState) addCall(call *Syscall) { | ||
| if rs.calls[call] { | ||
| return | ||
| } | ||
| rs.calls[call] = true | ||
| for _, res := range rs.syscallUses[call] { | ||
| if rs.topHandled[res] || rs.depHandled[res] { | ||
| continue | ||
| } | ||
| rs.depHandled[res] = true | ||
| rs.depQueue = append(rs.depQueue, res) | ||
| } | ||
| } | ||
|
|
||
| func (rs *rotatorState) selectCalls(set []*Syscall, probability int, force bool) { | ||
| if !force && probability < 2 { | ||
| panic("will never select anything") | ||
| } | ||
| for ; len(set) != 0 && (force || rs.rnd.Intn(probability) != 0); force = false { | ||
| call := set[rs.rnd.Intn(len(set))] | ||
| rs.addCall(call) | ||
| } | ||
| } |
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