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// Copyright 2018 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 safecopy provides an efficient implementation of functions to access
// memory that may result in SIGSEGV or SIGBUS being sent to the accessor.
package safecopy
import (
"fmt"
"runtime"
"golang.org/x/sys/unix"
"gvisor.dev/gvisor/pkg/errors"
"gvisor.dev/gvisor/pkg/errors/linuxerr"
"gvisor.dev/gvisor/pkg/sighandling"
)
// SegvError is returned when a safecopy function receives SIGSEGV.
type SegvError struct {
// Addr is the address at which the SIGSEGV occurred.
Addr uintptr
}
// Error implements error.Error.
func (e SegvError) Error() string {
return fmt.Sprintf("SIGSEGV at %#x", e.Addr)
}
// BusError is returned when a safecopy function receives SIGBUS.
type BusError struct {
// Addr is the address at which the SIGBUS occurred.
Addr uintptr
}
// Error implements error.Error.
func (e BusError) Error() string {
return fmt.Sprintf("SIGBUS at %#x", e.Addr)
}
// AlignmentError is returned when a safecopy function is passed an address
// that does not meet alignment requirements.
type AlignmentError struct {
// Addr is the invalid address.
Addr uintptr
// Alignment is the required alignment.
Alignment uintptr
}
// Error implements error.Error.
func (e AlignmentError) Error() string {
return fmt.Sprintf("address %#x is not aligned to a %d-byte boundary", e.Addr, e.Alignment)
}
var (
// The begin and end addresses below are for the functions that are
// checked by the signal handler.
memcpyBegin uintptr
memcpyEnd uintptr
memclrBegin uintptr
memclrEnd uintptr
swapUint32Begin uintptr
swapUint32End uintptr
swapUint64Begin uintptr
swapUint64End uintptr
compareAndSwapUint32Begin uintptr
compareAndSwapUint32End uintptr
loadUint32Begin uintptr
loadUint32End uintptr
// savedSigSegVHandler is a pointer to the SIGSEGV handler that was
// configured before we replaced it with our own. We still call into it
// when we get a SIGSEGV that is not interesting to us.
savedSigSegVHandler uintptr
// Same as above, but for SIGBUS signals.
savedSigBusHandler uintptr
)
// signalHandler is our replacement signal handler for SIGSEGV and SIGBUS
// signals.
func signalHandler()
// addrOfSignalHandler returns the start address of signalHandler.
//
// See comment on addrOfMemcpy for more details.
func addrOfSignalHandler() uintptr
// FindEndAddress returns the end address (one byte beyond the last) of the
// function that contains the specified address (begin).
func FindEndAddress(begin uintptr) uintptr {
f := runtime.FuncForPC(begin)
if f != nil {
for p := begin; ; p++ {
g := runtime.FuncForPC(p)
if f != g {
return p
}
}
}
return begin
}
// initializeAddresses initializes the addresses used by the signal handler.
func initializeAddresses() {
// The following functions are written in assembly language, so they won't
// be inlined by the existing compiler/linker. Tests will fail if this
// assumption is violated.
memcpyBegin = addrOfMemcpy()
memcpyEnd = FindEndAddress(memcpyBegin)
memclrBegin = addrOfMemclr()
memclrEnd = FindEndAddress(memclrBegin)
swapUint32Begin = addrOfSwapUint32()
swapUint32End = FindEndAddress(swapUint32Begin)
swapUint64Begin = addrOfSwapUint64()
swapUint64End = FindEndAddress(swapUint64Begin)
compareAndSwapUint32Begin = addrOfCompareAndSwapUint32()
compareAndSwapUint32End = FindEndAddress(compareAndSwapUint32Begin)
loadUint32Begin = addrOfLoadUint32()
loadUint32End = FindEndAddress(loadUint32Begin)
}
func init() {
initializeAddresses()
if err := sighandling.ReplaceSignalHandler(unix.SIGSEGV, addrOfSignalHandler(), &savedSigSegVHandler); err != nil {
panic(fmt.Sprintf("Unable to set handler for SIGSEGV: %v", err))
}
if err := sighandling.ReplaceSignalHandler(unix.SIGBUS, addrOfSignalHandler(), &savedSigBusHandler); err != nil {
panic(fmt.Sprintf("Unable to set handler for SIGBUS: %v", err))
}
linuxerr.AddErrorUnwrapper(func(e error) (*errors.Error, bool) {
switch e.(type) {
case SegvError, BusError, AlignmentError:
return linuxerr.EFAULT, true
default:
return nil, false
}
})
}
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