package systrap

import "gvisor.dev/gvisor/pkg/sentry/platform/systrap"

Package systrap provides a seccomp-based implementation of the platform interface.

In a nutshell, it works as follows:

The creation of a new address space creates a new child processes.

The creation of a new stub thread creates a new system thread with a specified address space. To initialize this thread, the following action will be done:

• install a signal stack which is shared with the Sentry.
• install a signal handler for SYS, BUS, FPE, CHLD, TRAP, SEGV signals. This signal handler is a key part of the systrap platform. Any stub event which has to be handled in a privilege mode (by the Sentry) triggers one of previous signals. The signal handler is running on the separate stack which is shared with the Sentry. There is the sysmsg structure to synchronize the Sentry and a stub thread.
• install seccomp filters to trap user system calls.
• send a fake SIGSEGV to stop the thread in the signal handler.

A platformContext is just a collection of temporary variables. Calling Switch on a platformContext does the following:

Set up proper registers and an FPU state on a stub signal frame.
Wake up a stub thread by changing sysmsg->stage and calling FUTEX_WAKE.
Wait for new stub event by polling sysmsg->stage.

Lock order:

subprocessPool.mu
	subprocess.mu
		platformContext.mu

+checkalignedignore

Index ¶

• Constants
• Variables
• type Systrap
• func New(opts platform.Options) (*Systrap, error)
• func (*Systrap) CooperativelySchedulesAddressSpace() bool
• func (*Systrap) MapUnit() uint64
• func (*Systrap) MaxUserAddress() hostarch.Addr
• func (*Systrap) MinUserAddress() hostarch.Addr
• func (p *Systrap) NewAddressSpace(any) (platform.AddressSpace, <-chan struct{}, error)
• func (*Systrap) NewContext(ctx pkgcontext.Context) platform.Context
• func (p *Systrap) SeccompInfo() platform.SeccompInfo
• func (*Systrap) SupportsAddressSpaceIO() bool

Constants ¶

const (
	ERESTARTSYS    = unix.Errno(512)
	ERESTARTNOINTR = unix.Errno(513)
	ERESTARTNOHAND = unix.Errno(514)
)

Linux kernel errnos which "should never be seen by user programs", but will be revealed to ptrace syscall exit tracing.

These constants are only used in subprocess.go.

Variables ¶

var SystrapProfiling = metric.FakeMetricBuilder{}

SystrapProfiling is a builder that produces conditionally compiled metrics. Metrics made from this are compiled and active at runtime when the "systrap_profiling" go-tag is specified at compilation.

Types ¶

type Systrap ¶

type Systrap struct {
	platform.NoCPUPreemptionDetection
	platform.UseHostGlobalMemoryBarrier
	// contains filtered or unexported fields
}

Systrap represents a collection of seccomp subprocesses.

func New ¶

func New(opts platform.Options) (*Systrap, error)

New returns a new seccomp-based implementation of the platform interface.

func (*Systrap) CooperativelySchedulesAddressSpace ¶

func (*Systrap) CooperativelySchedulesAddressSpace() bool

CooperativelySchedulesAddressSpace implements platform.Platform.CooperativelySchedulesAddressSpace.

func (*Systrap) MapUnit ¶

func (*Systrap) MapUnit() uint64

MapUnit implements platform.Platform.MapUnit.

func (*Systrap) MaxUserAddress ¶

func (*Systrap) MaxUserAddress() hostarch.Addr

MaxUserAddress returns the first address that may not be used by user applications.

func (*Systrap) MinUserAddress ¶

func (*Systrap) MinUserAddress() hostarch.Addr

MinUserAddress implements platform.MinUserAddress.

func (*Systrap) NewAddressSpace ¶

func (p *Systrap) NewAddressSpace(any) (platform.AddressSpace, <-chan struct{}, error)

NewAddressSpace returns a new subprocess.

func (*Systrap) NewContext ¶

func (*Systrap) NewContext(ctx pkgcontext.Context) platform.Context

NewContext returns an interruptible platformContext.

func (*Systrap) SeccompInfo ¶

func (p *Systrap) SeccompInfo() platform.SeccompInfo

SeccompInfo returns seccomp filter info for the systrap platform.

func (*Systrap) SupportsAddressSpaceIO ¶

func (*Systrap) SupportsAddressSpaceIO() bool

SupportsAddressSpaceIO implements platform.Platform.SupportsAddressSpaceIO.

Source Files ¶

context_queue.go context_queue_unsafe.go filters.go filters_amd64.go metrics.go shared_context.go shared_context_norace.go stub_defs.go stub_unsafe.go subprocess.go subprocess_amd64.go subprocess_linux.go subprocess_linux_unsafe.go subprocess_pool.go subprocess_unsafe.go syscall_thread.go syscall_thread_amd64.go syscall_thread_defs.go syscall_thread_unsafe.go sysmsg_thread.go sysmsg_thread_amd64.go sysmsg_thread_unsafe.go systrap.go systrap_amd64.go systrap_profiling_fake.go systrap_unsafe.go

Directories ¶