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Add BPFAction type with Stringer 

PiperOrigin-RevId: 226018694
Change-Id: I98965e26fe565f37e98e5df5f997363ab273c91b
This commit is contained in:
Fabricio Voznika 2018-12-18 10:27:16 -08:00 committed by Shentubot
parent e7b47844d9
commit 03226cd950
7 changed files with 112 additions and 88 deletions
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44
pkg/abi/linux/seccomp.go
View File

@ -14,18 +14,14 @@
package linux
import "fmt"
// Seccomp constants taken from <linux/seccomp.h>.
const (
SECCOMP_MODE_NONE = 0
SECCOMP_MODE_FILTER = 2
SECCOMP_RET_KILL_PROCESS = 0x80000000
SECCOMP_RET_KILL_THREAD = 0x00000000
SECCOMP_RET_TRAP = 0x00030000
SECCOMP_RET_ERRNO = 0x00050000
SECCOMP_RET_TRACE = 0x7ff00000
SECCOMP_RET_ALLOW = 0x7fff0000
SECCOMP_RET_ACTION_FULL = 0xffff0000
SECCOMP_RET_ACTION = 0x7fff0000
SECCOMP_RET_DATA = 0x0000ffff
@ -33,3 +29,37 @@ const (
SECCOMP_FILTER_FLAG_TSYNC = 1
SECCOMP_GET_ACTION_AVAIL = 2
)
type BPFAction uint32
const (
SECCOMP_RET_KILL_PROCESS BPFAction = 0x80000000
SECCOMP_RET_KILL_THREAD = 0x00000000
SECCOMP_RET_TRAP = 0x00030000
SECCOMP_RET_ERRNO = 0x00050000
SECCOMP_RET_TRACE = 0x7ff00000
SECCOMP_RET_ALLOW = 0x7fff0000
)
func (a BPFAction) String() string {
switch a & SECCOMP_RET_ACTION_FULL {
case SECCOMP_RET_KILL_PROCESS:
return "kill process"
case SECCOMP_RET_KILL_THREAD:
return "kill thread"
case SECCOMP_RET_TRAP:
return fmt.Sprintf("trap (%d)", a.Data())
case SECCOMP_RET_ERRNO:
return fmt.Sprintf("errno (%d)", a.Data())
case SECCOMP_RET_TRACE:
return fmt.Sprintf("trace (%d)", a.Data())
case SECCOMP_RET_ALLOW:
return "allow"
}
return fmt.Sprintf("invalid action: %#x", a)
}
// Data returns the SECCOMP_RET_DATA portion of the action.
func (a BPFAction) Data() uint16 {
return uint16(a & SECCOMP_RET_DATA)
}

32
pkg/seccomp/seccomp.go
View File

@ -33,16 +33,6 @@ const (
defaultLabel = "default_action"
)
func actionName(a uint32) string {
switch a {
case linux.SECCOMP_RET_KILL_PROCESS:
return "kill process"
case linux.SECCOMP_RET_TRAP:
return "trap"
}
panic(fmt.Sprintf("invalid action: %d", a))
}
// Install generates BPF code based on the set of syscalls provided. It only
// allows syscalls that conform to the specification. Syscalls that violate the
// specification will trigger RET_KILL_PROCESS, except for the cases below.
@ -67,12 +57,12 @@ func Install(rules SyscallRules) error {
// Uncomment to get stack trace when there is a violation.
// defaultAction = uint32(linux.SECCOMP_RET_TRAP)
log.Infof("Installing seccomp filters for %d syscalls (action=%s)", len(rules), actionName(defaultAction))
log.Infof("Installing seccomp filters for %d syscalls (action=%v)", len(rules), defaultAction)
instrs, err := BuildProgram([]RuleSet{
RuleSet{
Rules: rules,
Action: uint32(linux.SECCOMP_RET_ALLOW),
Action: linux.SECCOMP_RET_ALLOW,
},
}, defaultAction)
if log.IsLogging(log.Debug) {
@ -95,21 +85,21 @@ func Install(rules SyscallRules) error {
return nil
}
func defaultAction() (uint32, error) {
func defaultAction() (linux.BPFAction, error) {
available, err := isKillProcessAvailable()
if err != nil {
return 0, err
}
if available {
return uint32(linux.SECCOMP_RET_KILL_PROCESS), nil
return linux.SECCOMP_RET_KILL_PROCESS, nil
}
return uint32(linux.SECCOMP_RET_TRAP), nil
return linux.SECCOMP_RET_TRAP, nil
}
// RuleSet is a set of rules and associated action.
type RuleSet struct {
Rules SyscallRules
Action uint32
Action linux.BPFAction
// Vsyscall indicates that a check is made for a function being called
// from kernel mappings. This is where the vsyscall page is located
@ -127,7 +117,7 @@ var SyscallName = func(sysno uintptr) string {
// BuildProgram builds a BPF program from the given map of actions to matching
// SyscallRules. The single generated program covers all provided RuleSets.
func BuildProgram(rules []RuleSet, defaultAction uint32) ([]linux.BPFInstruction, error) {
func BuildProgram(rules []RuleSet, defaultAction linux.BPFAction) ([]linux.BPFInstruction, error) {
program := bpf.NewProgramBuilder()
// Be paranoid and check that syscall is done in the expected architecture.
@ -147,7 +137,7 @@ func BuildProgram(rules []RuleSet, defaultAction uint32) ([]linux.BPFInstruction
if err := program.AddLabel(defaultLabel); err != nil {
return nil, err
}
program.AddStmt(bpf.Ret|bpf.K, defaultAction)
program.AddStmt(bpf.Ret|bpf.K, uint32(defaultAction))
return program.Instructions()
}
@ -217,7 +207,7 @@ func checkArgsLabel(sysno uintptr) string {
// not insert a jump to the default action at the end and it is the
// responsibility of the caller to insert an appropriate jump after calling
// this function.
func addSyscallArgsCheck(p *bpf.ProgramBuilder, rules []Rule, action uint32, ruleSetIdx int, sysno uintptr) error {
func addSyscallArgsCheck(p *bpf.ProgramBuilder, rules []Rule, action linux.BPFAction, ruleSetIdx int, sysno uintptr) error {
for ruleidx, rule := range rules {
labelled := false
for i, arg := range rule {
@ -240,7 +230,7 @@ func addSyscallArgsCheck(p *bpf.ProgramBuilder, rules []Rule, action uint32, rul
}
// Matched, emit the given action.
p.AddStmt(bpf.Ret|bpf.K, action)
p.AddStmt(bpf.Ret|bpf.K, uint32(action))
// Label the end of the rule if necessary. This is added for
// the jumps above when the argument check fails.
@ -319,7 +309,7 @@ func buildBSTProgram(n *node, rules []RuleSet, program *bpf.ProgramBuilder) erro
// Emit matchers.
if len(rs.Rules[sysno]) == 0 {
// This is a blanket action.
program.AddStmt(bpf.Ret|bpf.K, rs.Action)
program.AddStmt(bpf.Ret|bpf.K, uint32(rs.Action))
emitted = true
} else {
// Add an argument check for these particular

14
pkg/seccomp/seccomp_test.go
View File

@ -72,12 +72,12 @@ func TestBasic(t *testing.T) {
data seccompData
// want is the expected return value of the BPF program.
want uint32
want linux.BPFAction
}
for _, test := range []struct {
ruleSets []RuleSet
defaultAction uint32
defaultAction linux.BPFAction
specs []spec
}{
{
@ -357,7 +357,7 @@ func TestBasic(t *testing.T) {
t.Errorf("%s: bpf.Exec() got error: %v", spec.desc, err)
continue
}
if got != spec.want {
if got != uint32(spec.want) {
t.Errorf("%s: bpd.Exec() = %d, want: %d", spec.desc, got, spec.want)
}
}
@ -380,9 +380,9 @@ func TestRandom(t *testing.T) {
instrs, err := BuildProgram([]RuleSet{
RuleSet{
Rules: syscallRules,
Action: uint32(linux.SECCOMP_RET_ALLOW),
Action: linux.SECCOMP_RET_ALLOW,
},
}, uint32(linux.SECCOMP_RET_TRAP))
}, linux.SECCOMP_RET_TRAP)
if err != nil {
t.Fatalf("buildProgram() got error: %v", err)
}
@ -397,11 +397,11 @@ func TestRandom(t *testing.T) {
t.Errorf("bpf.Exec() got error: %v, for syscall %d", err, i)
continue
}
want := uint32(linux.SECCOMP_RET_TRAP)
want := linux.SECCOMP_RET_TRAP
if _, ok := syscallRules[uintptr(i)]; ok {
want = linux.SECCOMP_RET_ALLOW
}
if got != want {
if got != uint32(want) {
t.Errorf("bpf.Exec() = %d, want: %d, for syscall %d", got, want, i)
}
}

49
pkg/sentry/kernel/seccomp.go
View File

@ -27,24 +27,6 @@ import (
const maxSyscallFilterInstructions = 1 << 15
type seccompResult int
const (
// seccompResultDeny indicates that a syscall should not be executed.
seccompResultDeny seccompResult = iota
// seccompResultAllow indicates that a syscall should be executed.
seccompResultAllow
// seccompResultKill indicates that the task should be killed immediately,
// with the exit status indicating that the task was killed by SIGSYS.
seccompResultKill
// seccompResultTrace indicates that a ptracer was successfully notified as
// a result of a SECCOMP_RET_TRACE.
seccompResultTrace
)
// seccompData is equivalent to struct seccomp_data, which contains the data
// passed to seccomp-bpf filters.
type seccompData struct {
@ -83,48 +65,47 @@ func seccompSiginfo(t *Task, errno, sysno int32, ip usermem.Addr) *arch.SignalIn
// in because vsyscalls do not use the values in t.Arch().)
//
// Preconditions: The caller must be running on the task goroutine.
func (t *Task) checkSeccompSyscall(sysno int32, args arch.SyscallArguments, ip usermem.Addr) seccompResult {
result := t.evaluateSyscallFilters(sysno, args, ip)
switch result & linux.SECCOMP_RET_ACTION {
func (t *Task) checkSeccompSyscall(sysno int32, args arch.SyscallArguments, ip usermem.Addr) linux.BPFAction {
result := linux.BPFAction(t.evaluateSyscallFilters(sysno, args, ip))
action := result & linux.SECCOMP_RET_ACTION
switch action {
case linux.SECCOMP_RET_TRAP:
// "Results in the kernel sending a SIGSYS signal to the triggering
// task without executing the system call. ... The SECCOMP_RET_DATA
// portion of the return value will be passed as si_errno." -
// Documentation/prctl/seccomp_filter.txt
t.SendSignal(seccompSiginfo(t, int32(result&linux.SECCOMP_RET_DATA), sysno, ip))
return seccompResultDeny
t.SendSignal(seccompSiginfo(t, int32(result.Data()), sysno, ip))
case linux.SECCOMP_RET_ERRNO:
// "Results in the lower 16-bits of the return value being passed to
// userland as the errno without executing the system call."
t.Arch().SetReturn(-uintptr(result & linux.SECCOMP_RET_DATA))
return seccompResultDeny
t.Arch().SetReturn(-uintptr(result.Data()))
case linux.SECCOMP_RET_TRACE:
// "When returned, this value will cause the kernel to attempt to
// notify a ptrace()-based tracer prior to executing the system call.
// If there is no tracer present, -ENOSYS is returned to userland and
// the system call is not executed."
if t.ptraceSeccomp(uint16(result & linux.SECCOMP_RET_DATA)) {
return seccompResultTrace
}
if !t.ptraceSeccomp(result.Data()) {
// This useless-looking temporary is needed because Go.
tmp := uintptr(syscall.ENOSYS)
t.Arch().SetReturn(-tmp)
return seccompResultDeny
return linux.SECCOMP_RET_ERRNO
}
case linux.SECCOMP_RET_ALLOW:
// "Results in the system call being executed."
return seccompResultAllow
case linux.SECCOMP_RET_KILL_THREAD:
// "Results in the task exiting immediately without executing the
// system call. The exit status of the task will be SIGSYS, not
// SIGKILL."
fallthrough
default: // consistent with Linux
return seccompResultKill
default:
// consistent with Linux
return linux.SECCOMP_RET_KILL_THREAD
}
return action
}
func (t *Task) evaluateSyscallFilters(sysno int32, args arch.SyscallArguments, ip usermem.Addr) uint32 {
@ -155,7 +136,7 @@ func (t *Task) evaluateSyscallFilters(sysno int32, args arch.SyscallArguments, i
thisRet, err := bpf.Exec(f.([]bpf.Program)[i], input)
if err != nil {
t.Debugf("seccomp-bpf filter %d returned error: %v", i, err)
thisRet = linux.SECCOMP_RET_KILL_THREAD
thisRet = uint32(linux.SECCOMP_RET_KILL_THREAD)
}
// "If multiple filters exist, the return value for the evaluation of a
// given system call will always use the highest precedent value." -

18
pkg/sentry/kernel/task_syscall.go
View File

@ -199,16 +199,16 @@ func (t *Task) doSyscall() taskRunState {
// is rare), not needed for correctness.
if t.syscallFilters.Load() != nil {
switch r := t.checkSeccompSyscall(int32(sysno), args, usermem.Addr(t.Arch().IP())); r {
case seccompResultDeny:
case linux.SECCOMP_RET_ERRNO, linux.SECCOMP_RET_TRAP:
t.Debugf("Syscall %d: denied by seccomp", sysno)
return (*runSyscallExit)(nil)
case seccompResultAllow:
case linux.SECCOMP_RET_ALLOW:
// ok
case seccompResultKill:
case linux.SECCOMP_RET_KILL_THREAD:
t.Debugf("Syscall %d: killed by seccomp", sysno)
t.PrepareExit(ExitStatus{Signo: int(linux.SIGSYS)})
return (*runExit)(nil)
case seccompResultTrace:
case linux.SECCOMP_RET_TRACE:
t.Debugf("Syscall %d: stopping for PTRACE_EVENT_SECCOMP", sysno)
return (*runSyscallAfterPtraceEventSeccomp)(nil)
default:
@ -345,14 +345,18 @@ func (t *Task) doVsyscall(addr usermem.Addr, sysno uintptr) taskRunState {
args := t.Arch().SyscallArgs()
if t.syscallFilters.Load() != nil {
switch r := t.checkSeccompSyscall(int32(sysno), args, addr); r {
case seccompResultDeny:
case linux.SECCOMP_RET_ERRNO, linux.SECCOMP_RET_TRAP:
t.Debugf("vsyscall %d, caller %x: denied by seccomp", sysno, t.Arch().Value(caller))
return (*runApp)(nil)
case seccompResultAllow:
case linux.SECCOMP_RET_ALLOW:
// ok
case seccompResultTrace:
case linux.SECCOMP_RET_TRACE:
t.Debugf("vsyscall %d, caller %x: stopping for PTRACE_EVENT_SECCOMP", sysno, t.Arch().Value(caller))
return &runVsyscallAfterPtraceEventSeccomp{addr, sysno, caller}
case linux.SECCOMP_RET_KILL_THREAD:
t.Debugf("vsyscall %d: killed by seccomp", sysno)
t.PrepareExit(ExitStatus{Signo: int(linux.SIGSYS)})
return (*runExit)(nil)
default:
panic(fmt.Sprintf("Unknown seccomp result %d", r))
}

16
pkg/sentry/platform/ptrace/subprocess_linux.go
View File

@ -38,7 +38,7 @@ const syscallEvent syscall.Signal = 0x80
// Precondition: the runtime OS thread must be locked.
func probeSeccomp() bool {
// Create a completely new, destroyable process.
t, err := attachedThread(0, uint32(linux.SECCOMP_RET_ERRNO))
t, err := attachedThread(0, linux.SECCOMP_RET_ERRNO)
if err != nil {
panic(fmt.Sprintf("seccomp probe failed: %v", err))
}
@ -112,14 +112,14 @@ func createStub() (*thread, error) {
// ptrace emulation check. This simplifies using SYSEMU, since seccomp
// will never run for emulation. Seccomp will only run for injected
// system calls, and thus we can use RET_KILL as our violation action.
var defaultAction uint32
var defaultAction linux.BPFAction
if probeSeccomp() {
log.Infof("Latest seccomp behavior found (kernel >= 4.8 likely)")
defaultAction = uint32(linux.SECCOMP_RET_KILL_THREAD)
defaultAction = linux.SECCOMP_RET_KILL_THREAD
} else {
// We must rely on SYSEMU behavior; tracing with SYSEMU is broken.
log.Infof("Legacy seccomp behavior found (kernel < 4.8 likely)")
defaultAction = uint32(linux.SECCOMP_RET_ALLOW)
defaultAction = linux.SECCOMP_RET_ALLOW
}
// When creating the new child process, we specify SIGKILL as the
@ -135,7 +135,7 @@ func createStub() (*thread, error) {
// attachedThread returns a new attached thread.
//
// Precondition: the runtime OS thread must be locked.
func attachedThread(flags uintptr, defaultAction uint32) (*thread, error) {
func attachedThread(flags uintptr, defaultAction linux.BPFAction) (*thread, error) {
// Create a BPF program that allows only the system calls needed by the
// stub and all its children. This is used to create child stubs
// (below), so we must include the ability to fork, but otherwise lock
@ -148,11 +148,11 @@ func attachedThread(flags uintptr, defaultAction uint32) (*thread, error) {
syscall.SYS_TIME: {},
309: {}, // SYS_GETCPU.
},
Action: uint32(linux.SECCOMP_RET_TRAP),
Action: linux.SECCOMP_RET_TRAP,
Vsyscall: true,
},
}
if defaultAction != uint32(linux.SECCOMP_RET_ALLOW) {
if defaultAction != linux.SECCOMP_RET_ALLOW {
rules = append(rules, seccomp.RuleSet{
Rules: seccomp.SyscallRules{
syscall.SYS_CLONE: []seccomp.Rule{
@ -191,7 +191,7 @@ func attachedThread(flags uintptr, defaultAction uint32) (*thread, error) {
syscall.SYS_MMAP: {},
syscall.SYS_MUNMAP: {},
},
Action: uint32(linux.SECCOMP_RET_ALLOW),
Action: linux.SECCOMP_RET_ALLOW,
})
}
instrs, err := seccomp.BuildProgram(rules, defaultAction)

19
test/syscalls/linux/seccomp.cc
View File

@ -215,6 +215,25 @@ TEST(SeccompTest, SeccompAppliesToVsyscall) {
<< "status " << status;
}
TEST(SeccompTest, RetKillVsyscallCausesDeathBySIGSYS) {
SKIP_IF(!ASSERT_NO_ERRNO_AND_VALUE(IsVsyscallEnabled()));
pid_t const pid = fork();
if (pid == 0) {
// Register a signal handler for SIGSYS that we don't expect to be invoked.
RegisterSignalHandler(
SIGSYS, +[](int, siginfo_t*, void*) { _exit(1); });
ApplySeccompFilter(SYS_time, SECCOMP_RET_KILL);
vsyscall_time(nullptr); // Should result in death.
TEST_CHECK_MSG(false, "Survived invocation of test syscall");
}
ASSERT_THAT(pid, SyscallSucceeds());
int status;
ASSERT_THAT(waitpid(pid, &status, 0), SyscallSucceedsWithValue(pid));
EXPECT_TRUE(WIFSIGNALED(status) && WTERMSIG(status) == SIGSYS)
<< "status " << status;
}
TEST(SeccompTest, RetTraceWithoutPtracerReturnsENOSYS) {
pid_t const pid = fork();
if (pid == 0) {