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rotation.go
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rotation.go
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// 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
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,
resources: make(map[*ResourceDesc]rotatorResource),
}
var sorted []*Syscall
for call := range calls {
sorted = append(sorted, call)
}
sort.Slice(sorted, func(i, j int) bool {
return sorted[i].Name < sorted[j].Name
})
for _, call := range sorted {
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).
ForeachCallType(call, func(t Type, _ *TypeCtx) {
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.createsResources))
for _, res := range call.createsResources {
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.createsResources) == 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.
if len(rs.resources) == 0 {
return rs.Rotator.calls
}
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, true)
if nctors1 {
continue
}
rs.selectCalls(info.ctors[2], 2, true)
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[2], 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 call.usesResources {
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)
}
}