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Diffstat (limited to 'pkg/safecopy/safecopy_unsafe.go')
| -rw-r--r-- | pkg/safecopy/safecopy_unsafe.go | 361 |
1 files changed, 361 insertions, 0 deletions
diff --git a/pkg/safecopy/safecopy_unsafe.go b/pkg/safecopy/safecopy_unsafe.go new file mode 100644 index 000000000..41dd567f3 --- /dev/null +++ b/pkg/safecopy/safecopy_unsafe.go @@ -0,0 +1,361 @@ +// 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 + +import ( + "fmt" + "runtime" + "syscall" + "unsafe" +) + +// maxRegisterSize is the maximum register size used in memcpy and memclr. It +// is used to decide by how much to rewind the copy (for memcpy) or zeroing +// (for memclr) before proceeding. +const maxRegisterSize = 16 + +// memcpy copies data from src to dst. If a SIGSEGV or SIGBUS signal is received +// during the copy, it returns the address that caused the fault and the number +// of the signal that was received. Otherwise, it returns an unspecified address +// and a signal number of 0. +// +// Data is copied in order, such that if a fault happens at address p, it is +// safe to assume that all data before p-maxRegisterSize has already been +// successfully copied. +// +//go:noescape +func memcpy(dst, src uintptr, n uintptr) (fault uintptr, sig int32) + +// memclr sets the n bytes following ptr to zeroes. If a SIGSEGV or SIGBUS +// signal is received during the write, it returns the address that caused the +// fault and the number of the signal that was received. Otherwise, it returns +// an unspecified address and a signal number of 0. +// +// Data is written in order, such that if a fault happens at address p, it is +// safe to assume that all data before p-maxRegisterSize has already been +// successfully written. +// +//go:noescape +func memclr(ptr uintptr, n uintptr) (fault uintptr, sig int32) + +// swapUint32 atomically stores new into *ptr and returns (the previous *ptr +// value, 0). If a SIGSEGV or SIGBUS signal is received during the swap, the +// value of old is unspecified, and sig is the number of the signal that was +// received. +// +// Preconditions: ptr must be aligned to a 4-byte boundary. +// +//go:noescape +func swapUint32(ptr unsafe.Pointer, new uint32) (old uint32, sig int32) + +// swapUint64 atomically stores new into *ptr and returns (the previous *ptr +// value, 0). If a SIGSEGV or SIGBUS signal is received during the swap, the +// value of old is unspecified, and sig is the number of the signal that was +// received. +// +// Preconditions: ptr must be aligned to a 8-byte boundary. +// +//go:noescape +func swapUint64(ptr unsafe.Pointer, new uint64) (old uint64, sig int32) + +// compareAndSwapUint32 is like sync/atomic.CompareAndSwapUint32, but returns +// (the value previously stored at ptr, 0). If a SIGSEGV or SIGBUS signal is +// received during the operation, the value of prev is unspecified, and sig is +// the number of the signal that was received. +// +// Preconditions: ptr must be aligned to a 4-byte boundary. +// +//go:noescape +func compareAndSwapUint32(ptr unsafe.Pointer, old, new uint32) (prev uint32, sig int32) + +// LoadUint32 is like sync/atomic.LoadUint32, but operates with user memory. It +// may fail with SIGSEGV or SIGBUS if it is received while reading from ptr. +// +// Preconditions: ptr must be aligned to a 4-byte boundary. +// +//go:noescape +func loadUint32(ptr unsafe.Pointer) (val uint32, sig int32) + +// CopyIn copies len(dst) bytes from src to dst. It returns the number of bytes +// copied and an error if SIGSEGV or SIGBUS is received while reading from src. +func CopyIn(dst []byte, src unsafe.Pointer) (int, error) { + n, err := copyIn(dst, uintptr(src)) + runtime.KeepAlive(src) + return n, err +} + +// copyIn is the underlying definition for CopyIn. +func copyIn(dst []byte, src uintptr) (int, error) { + toCopy := uintptr(len(dst)) + if len(dst) == 0 { + return 0, nil + } + + fault, sig := memcpy(uintptr(unsafe.Pointer(&dst[0])), src, toCopy) + if sig == 0 { + return len(dst), nil + } + + if fault < src || fault >= src+toCopy { + panic(fmt.Sprintf("CopyIn raised signal %d at %#x, which is outside source [%#x, %#x)", sig, fault, src, src+toCopy)) + } + + // memcpy might have ended the copy up to maxRegisterSize bytes before + // fault, if an instruction caused a memory access that straddled two + // pages, and the second one faulted. Try to copy up to the fault. + var done int + if fault-src > maxRegisterSize { + done = int(fault - src - maxRegisterSize) + } + n, err := copyIn(dst[done:int(fault-src)], src+uintptr(done)) + done += n + if err != nil { + return done, err + } + return done, errorFromFaultSignal(fault, sig) +} + +// CopyOut copies len(src) bytes from src to dst. If returns the number of +// bytes done and an error if SIGSEGV or SIGBUS is received while writing to +// dst. +func CopyOut(dst unsafe.Pointer, src []byte) (int, error) { + n, err := copyOut(uintptr(dst), src) + runtime.KeepAlive(dst) + return n, err +} + +// copyOut is the underlying definition for CopyOut. +func copyOut(dst uintptr, src []byte) (int, error) { + toCopy := uintptr(len(src)) + if toCopy == 0 { + return 0, nil + } + + fault, sig := memcpy(dst, uintptr(unsafe.Pointer(&src[0])), toCopy) + if sig == 0 { + return len(src), nil + } + + if fault < dst || fault >= dst+toCopy { + panic(fmt.Sprintf("CopyOut raised signal %d at %#x, which is outside destination [%#x, %#x)", sig, fault, dst, dst+toCopy)) + } + + // memcpy might have ended the copy up to maxRegisterSize bytes before + // fault, if an instruction caused a memory access that straddled two + // pages, and the second one faulted. Try to copy up to the fault. + var done int + if fault-dst > maxRegisterSize { + done = int(fault - dst - maxRegisterSize) + } + n, err := copyOut(dst+uintptr(done), src[done:int(fault-dst)]) + done += n + if err != nil { + return done, err + } + return done, errorFromFaultSignal(fault, sig) +} + +// Copy copies toCopy bytes from src to dst. It returns the number of bytes +// copied and an error if SIGSEGV or SIGBUS is received while reading from src +// or writing to dst. +// +// Data is copied in order; if [src, src+toCopy) and [dst, dst+toCopy) overlap, +// the resulting contents of dst are unspecified. +func Copy(dst, src unsafe.Pointer, toCopy uintptr) (uintptr, error) { + n, err := copyN(uintptr(dst), uintptr(src), toCopy) + runtime.KeepAlive(dst) + runtime.KeepAlive(src) + return n, err +} + +// copyN is the underlying definition for Copy. +func copyN(dst, src uintptr, toCopy uintptr) (uintptr, error) { + if toCopy == 0 { + return 0, nil + } + + fault, sig := memcpy(dst, src, toCopy) + if sig == 0 { + return toCopy, nil + } + + // Did the fault occur while reading from src or writing to dst? + faultAfterSrc := ^uintptr(0) + if fault >= src { + faultAfterSrc = fault - src + } + faultAfterDst := ^uintptr(0) + if fault >= dst { + faultAfterDst = fault - dst + } + if faultAfterSrc >= toCopy && faultAfterDst >= toCopy { + panic(fmt.Sprintf("Copy raised signal %d at %#x, which is outside source [%#x, %#x) and destination [%#x, %#x)", sig, fault, src, src+toCopy, dst, dst+toCopy)) + } + faultedAfter := faultAfterSrc + if faultedAfter > faultAfterDst { + faultedAfter = faultAfterDst + } + + // memcpy might have ended the copy up to maxRegisterSize bytes before + // fault, if an instruction caused a memory access that straddled two + // pages, and the second one faulted. Try to copy up to the fault. + var done uintptr + if faultedAfter > maxRegisterSize { + done = faultedAfter - maxRegisterSize + } + n, err := copyN(dst+done, src+done, faultedAfter-done) + done += n + if err != nil { + return done, err + } + return done, errorFromFaultSignal(fault, sig) +} + +// ZeroOut writes toZero zero bytes to dst. It returns the number of bytes +// written and an error if SIGSEGV or SIGBUS is received while writing to dst. +func ZeroOut(dst unsafe.Pointer, toZero uintptr) (uintptr, error) { + n, err := zeroOut(uintptr(dst), toZero) + runtime.KeepAlive(dst) + return n, err +} + +// zeroOut is the underlying definition for ZeroOut. +func zeroOut(dst uintptr, toZero uintptr) (uintptr, error) { + if toZero == 0 { + return 0, nil + } + + fault, sig := memclr(dst, toZero) + if sig == 0 { + return toZero, nil + } + + if fault < dst || fault >= dst+toZero { + panic(fmt.Sprintf("ZeroOut raised signal %d at %#x, which is outside destination [%#x, %#x)", sig, fault, dst, dst+toZero)) + } + + // memclr might have ended the write up to maxRegisterSize bytes before + // fault, if an instruction caused a memory access that straddled two + // pages, and the second one faulted. Try to write up to the fault. + var done uintptr + if fault-dst > maxRegisterSize { + done = fault - dst - maxRegisterSize + } + n, err := zeroOut(dst+done, fault-dst-done) + done += n + if err != nil { + return done, err + } + return done, errorFromFaultSignal(fault, sig) +} + +// SwapUint32 is equivalent to sync/atomic.SwapUint32, except that it returns +// an error if SIGSEGV or SIGBUS is received while accessing ptr, or if ptr is +// not aligned to a 4-byte boundary. +func SwapUint32(ptr unsafe.Pointer, new uint32) (uint32, error) { + if addr := uintptr(ptr); addr&3 != 0 { + return 0, AlignmentError{addr, 4} + } + old, sig := swapUint32(ptr, new) + return old, errorFromFaultSignal(uintptr(ptr), sig) +} + +// SwapUint64 is equivalent to sync/atomic.SwapUint64, except that it returns +// an error if SIGSEGV or SIGBUS is received while accessing ptr, or if ptr is +// not aligned to an 8-byte boundary. +func SwapUint64(ptr unsafe.Pointer, new uint64) (uint64, error) { + if addr := uintptr(ptr); addr&7 != 0 { + return 0, AlignmentError{addr, 8} + } + old, sig := swapUint64(ptr, new) + return old, errorFromFaultSignal(uintptr(ptr), sig) +} + +// CompareAndSwapUint32 is equivalent to atomicbitops.CompareAndSwapUint32, +// except that it returns an error if SIGSEGV or SIGBUS is received while +// accessing ptr, or if ptr is not aligned to a 4-byte boundary. +func CompareAndSwapUint32(ptr unsafe.Pointer, old, new uint32) (uint32, error) { + if addr := uintptr(ptr); addr&3 != 0 { + return 0, AlignmentError{addr, 4} + } + prev, sig := compareAndSwapUint32(ptr, old, new) + return prev, errorFromFaultSignal(uintptr(ptr), sig) +} + +// LoadUint32 is like sync/atomic.LoadUint32, but operates with user memory. It +// may fail with SIGSEGV or SIGBUS if it is received while reading from ptr. +// +// Preconditions: ptr must be aligned to a 4-byte boundary. +func LoadUint32(ptr unsafe.Pointer) (uint32, error) { + if addr := uintptr(ptr); addr&3 != 0 { + return 0, AlignmentError{addr, 4} + } + val, sig := loadUint32(ptr) + return val, errorFromFaultSignal(uintptr(ptr), sig) +} + +func errorFromFaultSignal(addr uintptr, sig int32) error { + switch sig { + case 0: + return nil + case int32(syscall.SIGSEGV): + return SegvError{addr} + case int32(syscall.SIGBUS): + return BusError{addr} + default: + panic(fmt.Sprintf("safecopy got unexpected signal %d at address %#x", sig, addr)) + } +} + +// ReplaceSignalHandler replaces the existing signal handler for the provided +// signal with the one that handles faults in safecopy-protected functions. +// +// It stores the value of the previously set handler in previous. +// +// This function will be called on initialization in order to install safecopy +// handlers for appropriate signals. These handlers will call the previous +// handler however, and if this is function is being used externally then the +// same courtesy is expected. +func ReplaceSignalHandler(sig syscall.Signal, handler uintptr, previous *uintptr) error { + var sa struct { + handler uintptr + flags uint64 + restorer uintptr + mask uint64 + } + const maskLen = 8 + + // Get the existing signal handler information, and save the current + // handler. Once we replace it, we will use this pointer to fall back to + // it when we receive other signals. + if _, _, e := syscall.RawSyscall6(syscall.SYS_RT_SIGACTION, uintptr(sig), 0, uintptr(unsafe.Pointer(&sa)), maskLen, 0, 0); e != 0 { + return e + } + + // Fail if there isn't a previous handler. + if sa.handler == 0 { + return fmt.Errorf("previous handler for signal %x isn't set", sig) + } + + *previous = sa.handler + + // Install our own handler. + sa.handler = handler + if _, _, e := syscall.RawSyscall6(syscall.SYS_RT_SIGACTION, uintptr(sig), uintptr(unsafe.Pointer(&sa)), 0, maskLen, 0, 0); e != 0 { + return e + } + + return nil +} |