From dfa4b3b90861a61653d0bef8f144bb4e82d21d78 Mon Sep 17 00:00:00 2001 From: Jamie Liu Date: Wed, 23 Jun 2021 13:15:44 -0700 Subject: Move flipcall.packetWindowMmap to memutil. PiperOrigin-RevId: 381100861 --- pkg/flipcall/packet_window.go | 166 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 166 insertions(+) create mode 100644 pkg/flipcall/packet_window.go (limited to 'pkg/flipcall/packet_window.go') diff --git a/pkg/flipcall/packet_window.go b/pkg/flipcall/packet_window.go new file mode 100644 index 000000000..9122c97b7 --- /dev/null +++ b/pkg/flipcall/packet_window.go @@ -0,0 +1,166 @@ +// Copyright 2019 The gVisor Authors. +// +// 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 flipcall + +import ( + "fmt" + "math/bits" + "os" + + "golang.org/x/sys/unix" + "gvisor.dev/gvisor/pkg/abi/linux" + "gvisor.dev/gvisor/pkg/memutil" +) + +var ( + pageSize = os.Getpagesize() + pageMask = pageSize - 1 +) + +func init() { + if bits.OnesCount(uint(pageSize)) != 1 { + // This is depended on by roundUpToPage(). + panic(fmt.Sprintf("system page size (%d) is not a power of 2", pageSize)) + } + if uintptr(pageSize) < PacketHeaderBytes { + // This is required since Endpoint.Init() imposes a minimum packet + // window size of 1 page. + panic(fmt.Sprintf("system page size (%d) is less than packet header size (%d)", pageSize, PacketHeaderBytes)) + } +} + +// PacketWindowDescriptor represents a packet window, a range of pages in a +// shared memory file that is used to exchange packets between partner +// Endpoints. +type PacketWindowDescriptor struct { + // FD is the file descriptor representing the shared memory file. + FD int + + // Offset is the offset into the shared memory file at which the packet + // window begins. + Offset int64 + + // Length is the size of the packet window in bytes. + Length int +} + +// PacketWindowLengthForDataCap returns the minimum packet window size required +// to accommodate datagrams of the given size in bytes. +func PacketWindowLengthForDataCap(dataCap uint32) int { + return roundUpToPage(int(dataCap) + int(PacketHeaderBytes)) +} + +func roundUpToPage(x int) int { + return (x + pageMask) &^ pageMask +} + +// A PacketWindowAllocator owns a shared memory file, and allocates packet +// windows from it. +type PacketWindowAllocator struct { + fd int + nextAlloc int64 + fileSize int64 +} + +// Init must be called on zero-value PacketWindowAllocators before first use. +// If it succeeds, Destroy() must be called once the PacketWindowAllocator is +// no longer in use. +func (pwa *PacketWindowAllocator) Init() error { + fd, err := memutil.CreateMemFD("flipcall_packet_windows", linux.MFD_CLOEXEC|linux.MFD_ALLOW_SEALING) + if err != nil { + return fmt.Errorf("failed to create memfd: %v", err) + } + // Apply F_SEAL_SHRINK to prevent either party from causing SIGBUS in the + // other by truncating the file, and F_SEAL_SEAL to prevent either party + // from applying F_SEAL_GROW or F_SEAL_WRITE. + if _, _, e := unix.RawSyscall(unix.SYS_FCNTL, uintptr(fd), linux.F_ADD_SEALS, linux.F_SEAL_SHRINK|linux.F_SEAL_SEAL); e != 0 { + unix.Close(fd) + return fmt.Errorf("failed to apply memfd seals: %v", e) + } + pwa.fd = fd + return nil +} + +// NewPacketWindowAllocator is a convenience function that returns an +// initialized PacketWindowAllocator allocated on the heap. +func NewPacketWindowAllocator() (*PacketWindowAllocator, error) { + var pwa PacketWindowAllocator + if err := pwa.Init(); err != nil { + return nil, err + } + return &pwa, nil +} + +// Destroy releases resources owned by pwa. This invalidates file descriptors +// previously returned by pwa.FD() and pwd.Allocate(). +func (pwa *PacketWindowAllocator) Destroy() { + unix.Close(pwa.fd) +} + +// FD represents the file descriptor of the shared memory file backing pwa. +func (pwa *PacketWindowAllocator) FD() int { + return pwa.fd +} + +// Allocate allocates a new packet window of at least the given size and +// returns a PacketWindowDescriptor representing it. +// +// Preconditions: size > 0. +func (pwa *PacketWindowAllocator) Allocate(size int) (PacketWindowDescriptor, error) { + if size <= 0 { + return PacketWindowDescriptor{}, fmt.Errorf("invalid size: %d", size) + } + // Page-align size to ensure that pwa.nextAlloc remains page-aligned. + size = roundUpToPage(size) + if size <= 0 { + return PacketWindowDescriptor{}, fmt.Errorf("size %d overflows after rounding up to page size", size) + } + end := pwa.nextAlloc + int64(size) // overflow checked by ensureFileSize + if err := pwa.ensureFileSize(end); err != nil { + return PacketWindowDescriptor{}, err + } + start := pwa.nextAlloc + pwa.nextAlloc = end + return PacketWindowDescriptor{ + FD: pwa.FD(), + Offset: start, + Length: size, + }, nil +} + +func (pwa *PacketWindowAllocator) ensureFileSize(min int64) error { + if min <= 0 { + return fmt.Errorf("file size would overflow") + } + if pwa.fileSize >= min { + return nil + } + newSize := 2 * pwa.fileSize + if newSize == 0 { + newSize = int64(pageSize) + } + for newSize < min { + newNewSize := newSize * 2 + if newNewSize <= 0 { + return fmt.Errorf("file size would overflow") + } + newSize = newNewSize + } + if err := unix.Ftruncate(pwa.FD(), newSize); err != nil { + return fmt.Errorf("ftruncate failed: %v", err) + } + pwa.fileSize = newSize + return nil +} -- cgit v1.2.3