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// Copyright 2018 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// Package platform provides a Platform abstraction.
//
// See Platform for more information.
package platform
import (
"fmt"
"io"
"gvisor.googlesource.com/gvisor/pkg/abi/linux"
"gvisor.googlesource.com/gvisor/pkg/sentry/arch"
"gvisor.googlesource.com/gvisor/pkg/sentry/safemem"
"gvisor.googlesource.com/gvisor/pkg/sentry/usage"
"gvisor.googlesource.com/gvisor/pkg/sentry/usermem"
)
// Platform provides abstractions for execution contexts (Context) and memory
// management (Memory, AddressSpace).
type Platform interface {
// SupportsAddressSpaceIO returns true if AddressSpaces returned by this
// Platform support AddressSpaceIO methods.
//
// The value returned by SupportsAddressSpaceIO is guaranteed to remain
// unchanged over the lifetime of the Platform.
SupportsAddressSpaceIO() bool
// CooperativelySchedulesAddressSpace returns true if the Platform has a
// limited number of AddressSpaces, such that mm.MemoryManager.Deactivate
// should call AddressSpace.Release when there are no goroutines that
// require the mm.MemoryManager to have an active AddressSpace.
//
// The value returned by CooperativelySchedulesAddressSpace is guaranteed
// to remain unchanged over the lifetime of the Platform.
CooperativelySchedulesAddressSpace() bool
// DetectsCPUPreemption returns true if Contexts returned by the Platform
// can reliably return ErrContextCPUPreempted.
DetectsCPUPreemption() bool
// MapUnit returns the alignment used for optional mappings into this
// platform's AddressSpaces. Higher values indicate lower per-page
// costs for AddressSpace.MapInto. As a special case, a MapUnit of 0
// indicates that the cost of AddressSpace.MapInto is effectively
// independent of the number of pages mapped. If MapUnit is non-zero,
// it must be a power-of-2 multiple of usermem.PageSize.
MapUnit() uint64
// MinUserAddress returns the minimum mappable address on this
// platform.
MinUserAddress() usermem.Addr
// MaxUserAddress returns the maximum mappable address on this
// platform.
MaxUserAddress() usermem.Addr
// NewAddressSpace returns a new memory context for this platform.
//
// If mappingsID is not nil, the platform may assume that (1) all calls
// to NewAddressSpace with the same mappingsID represent the same
// (mutable) set of mappings, and (2) the set of mappings has not
// changed since the last time AddressSpace.Release was called on an
// AddressSpace returned by a call to NewAddressSpace with the same
// mappingsID.
//
// If a new AddressSpace cannot be created immediately, a nil
// AddressSpace is returned, along with channel that is closed when
// the caller should retry a call to NewAddressSpace.
//
// In general, this blocking behavior only occurs when
// CooperativelySchedulesAddressSpace (above) returns false.
NewAddressSpace(mappingsID interface{}) (AddressSpace, <-chan struct{}, error)
// NewContext returns a new execution context.
NewContext() Context
// Memory returns memory for allocations.
Memory() Memory
// PreemptAllCPUs causes all concurrent calls to Context.Switch(), as well
// as the first following call to Context.Switch() for each Context, to
// return ErrContextCPUPreempted.
//
// PreemptAllCPUs is only supported if DetectsCPUPremption() == true.
// Platforms for which this does not hold may panic if PreemptAllCPUs is
// called.
PreemptAllCPUs() error
}
// NoCPUPreemptionDetection implements Platform.DetectsCPUPreemption and
// dependent methods for Platforms that do not support this feature.
type NoCPUPreemptionDetection struct{}
// DetectsCPUPreemption implements Platform.DetectsCPUPreemption.
func (NoCPUPreemptionDetection) DetectsCPUPreemption() bool {
return false
}
// PreemptAllCPUs implements Platform.PreemptAllCPUs.
func (NoCPUPreemptionDetection) PreemptAllCPUs() error {
panic("This platform does not support CPU preemption detection")
}
// Context represents the execution context for a single thread.
type Context interface {
// Switch resumes execution of the thread specified by the arch.Context
// in the provided address space. This call will block while the thread
// is executing.
//
// If cpu is non-negative, and it is not the number of the CPU that the
// thread executes on, Context should return ErrContextCPUPreempted. cpu
// can only be non-negative if Platform.DetectsCPUPreemption() is true;
// Contexts from Platforms for which this does not hold may ignore cpu, or
// panic if cpu is non-negative.
//
// Switch may return one of the following special errors:
//
// - nil: The Context invoked a system call.
//
// - ErrContextSignal: The Context was interrupted by a signal. The
// returned *arch.SignalInfo contains information about the signal. If
// arch.SignalInfo.Signo == SIGSEGV, the returned usermem.AccessType
// contains the access type of the triggering fault. The caller owns
// the returned SignalInfo.
//
// - ErrContextInterrupt: The Context was interrupted by a call to
// Interrupt(). Switch() may return ErrContextInterrupt spuriously. In
// particular, most implementations of Interrupt() will cause the first
// following call to Switch() to return ErrContextInterrupt if there is no
// concurrent call to Switch().
//
// - ErrContextCPUPreempted: See the definition of that error for details.
Switch(as AddressSpace, ac arch.Context, cpu int32) (*arch.SignalInfo, usermem.AccessType, error)
// Interrupt interrupts a concurrent call to Switch(), causing it to return
// ErrContextInterrupt.
Interrupt()
}
var (
// ErrContextSignal is returned by Context.Switch() to indicate that the
// Context was interrupted by a signal.
ErrContextSignal = fmt.Errorf("interrupted by signal")
// ErrContextSignalCPUID is equivalent to ErrContextSignal, except that
// a check should be done for execution of the CPUID instruction. If
// the current instruction pointer is a CPUID instruction, then this
// should be emulated appropriately. If not, then the given signal
// should be handled per above.
ErrContextSignalCPUID = fmt.Errorf("interrupted by signal, possible CPUID")
// ErrContextInterrupt is returned by Context.Switch() to indicate that the
// Context was interrupted by a call to Context.Interrupt().
ErrContextInterrupt = fmt.Errorf("interrupted by platform.Context.Interrupt()")
// ErrContextCPUPreempted is returned by Context.Switch() to indicate that
// one of the following occurred:
//
// - The CPU executing the Context is not the CPU passed to
// Context.Switch().
//
// - The CPU executing the Context may have executed another Context since
// the last time it executed this one; or the CPU has previously executed
// another Context, and has never executed this one.
//
// - Platform.PreemptAllCPUs() was called since the last return from
// Context.Switch().
ErrContextCPUPreempted = fmt.Errorf("interrupted by CPU preemption")
)
// SignalInterrupt is a signal reserved for use by implementations of
// Context.Interrupt(). The sentry guarantees that it will ignore delivery of
// this signal both to Contexts and to the sentry itself, under the assumption
// that they originate from races with Context.Interrupt().
//
// NOTE: The Go runtime only guarantees that a small subset
// of signals will be always be unblocked on all threads, one of which
// is SIGCHLD.
const SignalInterrupt = linux.SIGCHLD
// AddressSpace represents a virtual address space in which a Context can
// execute.
type AddressSpace interface {
// MapFile creates a shared mapping of offsets in fr, from the file
// with file descriptor fd, at address addr. Any existing overlapping
// mappings are silently replaced.
//
// If precommit is true, host memory should be committed to the mapping
// when MapFile returns when possible. The precommit flag is advisory
// and implementations may choose to ignore it.
//
// Preconditions: addr and fr must be page-aligned. length > 0.
// at.Any() == true.
MapFile(addr usermem.Addr, fd int, fr FileRange, at usermem.AccessType, precommit bool) error
// Unmap unmaps the given range.
//
// Preconditions: addr is page-aligned. length > 0.
Unmap(addr usermem.Addr, length uint64)
// Release releases this address space. After releasing, a new AddressSpace
// must be acquired via platform.NewAddressSpace().
Release()
// AddressSpaceIO methods are supported iff the associated platform's
// Platform.SupportsAddressSpaceIO() == true. AddressSpaces for which this
// does not hold may panic if AddressSpaceIO methods are invoked.
AddressSpaceIO
}
// AddressSpaceIO supports IO through the memory mappings installed in an
// AddressSpace.
//
// AddressSpaceIO implementors are responsible for ensuring that address ranges
// are application-mappable.
type AddressSpaceIO interface {
// CopyOut copies len(src) bytes from src to the memory mapped at addr. It
// returns the number of bytes copied. If the number of bytes copied is <
// len(src), it returns a non-nil error explaining why.
CopyOut(addr usermem.Addr, src []byte) (int, error)
// CopyIn copies len(dst) bytes from the memory mapped at addr to dst.
// It returns the number of bytes copied. If the number of bytes copied is
// < len(dst), it returns a non-nil error explaining why.
CopyIn(addr usermem.Addr, dst []byte) (int, error)
// ZeroOut sets toZero bytes to 0, starting at addr. It returns the number
// of bytes zeroed. If the number of bytes zeroed is < toZero, it returns a
// non-nil error explaining why.
ZeroOut(addr usermem.Addr, toZero uintptr) (uintptr, error)
// SwapUint32 atomically sets the uint32 value at addr to new and returns
// the previous value.
//
// Preconditions: addr must be aligned to a 4-byte boundary.
SwapUint32(addr usermem.Addr, new uint32) (uint32, error)
// CompareAndSwapUint32 atomically compares the uint32 value at addr to
// old; if they are equal, the value in memory is replaced by new. In
// either case, the previous value stored in memory is returned.
//
// Preconditions: addr must be aligned to a 4-byte boundary.
CompareAndSwapUint32(addr usermem.Addr, old, new uint32) (uint32, error)
}
// NoAddressSpaceIO implements AddressSpaceIO methods by panicing.
type NoAddressSpaceIO struct{}
// CopyOut implements AddressSpaceIO.CopyOut.
func (NoAddressSpaceIO) CopyOut(addr usermem.Addr, src []byte) (int, error) {
panic("This platform does not support AddressSpaceIO")
}
// CopyIn implements AddressSpaceIO.CopyIn.
func (NoAddressSpaceIO) CopyIn(addr usermem.Addr, dst []byte) (int, error) {
panic("This platform does not support AddressSpaceIO")
}
// ZeroOut implements AddressSpaceIO.ZeroOut.
func (NoAddressSpaceIO) ZeroOut(addr usermem.Addr, toZero uintptr) (uintptr, error) {
panic("This platform does not support AddressSpaceIO")
}
// SwapUint32 implements AddressSpaceIO.SwapUint32.
func (NoAddressSpaceIO) SwapUint32(addr usermem.Addr, new uint32) (uint32, error) {
panic("This platform does not support AddressSpaceIO")
}
// CompareAndSwapUint32 implements AddressSpaceIO.CompareAndSwapUint32.
func (NoAddressSpaceIO) CompareAndSwapUint32(addr usermem.Addr, old, new uint32) (uint32, error) {
panic("This platform does not support AddressSpaceIO")
}
// SegmentationFault is an error returned by AddressSpaceIO methods when IO
// fails due to access of an unmapped page, or a mapped page with insufficient
// permissions.
type SegmentationFault struct {
// Addr is the address at which the fault occurred.
Addr usermem.Addr
}
// Error implements error.Error.
func (f SegmentationFault) Error() string {
return fmt.Sprintf("segmentation fault at %#x", f.Addr)
}
// File represents a host file that may be mapped into an AddressSpace.
type File interface {
// MapInto maps fr into as, starting at addr, for accesses of type at.
//
// If precommit is true, the platform should eagerly commit resources (e.g.
// physical memory) to the mapping. The precommit flag is advisory and
// implementations may choose to ignore it.
//
// Note that there is no File.Unmap; clients should use as.Unmap directly.
//
// Preconditions: fr.Start and fr.End must be page-aligned.
// fr.Length() > 0. at.Any() == true. Implementors may define
// additional requirements.
MapInto(as AddressSpace, addr usermem.Addr, fr FileRange, at usermem.AccessType, precommit bool) error
// MapInternal returns a mapping of the given file offsets in the invoking
// process' address space for reading and writing. The returned mapping is
// valid as long as a reference is held on the mapped range.
//
// Note that fr.Start and fr.End need not be page-aligned.
//
// Preconditions: fr.Length() > 0. Implementors may define additional
// requirements.
MapInternal(fr FileRange, at usermem.AccessType) (safemem.BlockSeq, error)
// IncRef signals that a region in the file is actively referenced through a
// memory map. Implementors must ensure that the contents of a referenced
// region remain consistent. Specifically, mappings returned by MapInternal
// must refer to the same underlying contents. If the implementor also
// implements the Memory interface, the file range must not be reused in a
// different allocation while it has active references.
//
// Preconditions: fr.Start and fr.End must be page-aligned. fr.Length() > 0.
IncRef(fr FileRange)
// DecRef reduces the frame ref count on the range specified by fr.
//
// Preconditions: fr.Start and fr.End must be page-aligned. fr.Length() >
// 0. DecRef()s on a region must match earlier IncRef()s.
DecRef(fr FileRange)
}
// FileRange represents a range of uint64 offsets into a File.
//
// type FileRange <generated using go_generics>
// String implements fmt.Stringer.String.
func (fr FileRange) String() string {
return fmt.Sprintf("[%#x, %#x)", fr.Start, fr.End)
}
// Memory represents an allocatable File that may be mapped into any
// AddressSpace associated with the same Platform.
type Memory interface {
// Memory implements File methods with the following properties:
//
// - Pages mapped by MapInto must be allocated, and must be unmapped from
// all AddressSpaces before they are freed.
//
// - Pages mapped by MapInternal must be allocated. Returned mappings are
// guaranteed to be valid until the mapped pages are freed.
File
// Allocate returns a range of pages of the given length, owned by the
// caller and with the given accounting kind. Allocated memory initially has
// a single reference and will automatically be freed when no references to
// them remain. See File.IncRef and File.DecRef.
//
// Preconditions: length must be page-aligned and non-zero.
Allocate(length uint64, kind usage.MemoryKind) (FileRange, error)
// Decommit releases resources associated with maintaining the contents of
// the given frames. If Decommit succeeds, future accesses of the
// decommitted frames will read zeroes.
//
// Preconditions: fr.Length() > 0.
Decommit(fr FileRange) error
// UpdateUsage updates the memory usage statistics. This must be called
// before the relevant memory statistics in usage.MemoryAccounting can
// be considered accurate.
UpdateUsage() error
// TotalUsage returns an aggregate usage for all memory statistics
// except Mapped (which is external to the Memory implementation). This
// is generally much cheaper than UpdateUsage, but will not provide a
// fine-grained breakdown.
TotalUsage() (uint64, error)
// TotalSize returns the current maximum size of the Memory in bytes. The
// value returned by TotalSize is permitted to change.
TotalSize() uint64
// Destroy releases all resources associated with the Memory.
//
// Preconditions: There are no remaining uses of any of the freed memory's
// frames.
//
// Postconditions: None of the Memory's methods may be called after Destroy.
Destroy()
// SaveTo saves the memory state to the given stream, which will
// generally be a statefile.
SaveTo(w io.Writer) error
// LoadFrom loads the memory state from the given stream, which will
// generally be a statefile.
LoadFrom(r io.Reader) error
}
// AllocateAndFill allocates memory of the given kind from mem and fills it by
// calling r.ReadToBlocks() repeatedly until either length bytes are read or a
// non-nil error is returned. It returns the memory filled by r, truncated down
// to the nearest page. If this is shorter than length bytes due to an error
// returned by r.ReadToBlocks(), it returns that error.
//
// Preconditions: length > 0. length must be page-aligned.
func AllocateAndFill(mem Memory, length uint64, kind usage.MemoryKind, r safemem.Reader) (FileRange, error) {
fr, err := mem.Allocate(length, kind)
if err != nil {
return FileRange{}, err
}
dsts, err := mem.MapInternal(fr, usermem.Write)
if err != nil {
mem.DecRef(fr)
return FileRange{}, err
}
n, err := safemem.ReadFullToBlocks(r, dsts)
un := uint64(usermem.Addr(n).RoundDown())
if un < length {
// Free unused memory and update fr to contain only the memory that is
// still allocated.
mem.DecRef(FileRange{fr.Start + un, fr.End})
fr.End = fr.Start + un
}
return fr, err
}
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