1 files changed, 338 insertions, 0 deletions
diff --git a/pkg/sentry/kernel/kcov.go b/pkg/sentry/kernel/kcov.go
new file mode 100644
index 000000000..4fcdfc541
--- /dev/null
+++ b/pkg/sentry/kernel/kcov.go
@@ -0,0 +1,338 @@
+// Copyright 2020 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 kernel
+
+import (
+	"fmt"
+	"io"
+	"sync"
+
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/coverage"
+	"gvisor.dev/gvisor/pkg/safemem"
+	"gvisor.dev/gvisor/pkg/sentry/memmap"
+	"gvisor.dev/gvisor/pkg/sentry/mm"
+	"gvisor.dev/gvisor/pkg/sentry/pgalloc"
+	"gvisor.dev/gvisor/pkg/sentry/usage"
+	"gvisor.dev/gvisor/pkg/syserror"
+	"gvisor.dev/gvisor/pkg/usermem"
+)
+
+// kcovAreaSizeMax is the maximum number of uint64 entries allowed in the kcov
+// area. On Linux, the maximum is INT_MAX / 8.
+const kcovAreaSizeMax = 10 * 1024 * 1024
+
+// Kcov provides kernel coverage data to userspace through a memory-mapped
+// region, as kcov does in Linux.
+//
+// To give the illusion that the data is always up to date, we update the shared
+// memory every time before we return to userspace.
+type Kcov struct {
+	// mfp provides application memory. It is immutable after creation.
+	mfp pgalloc.MemoryFileProvider
+
+	// mu protects all of the fields below.
+	mu sync.RWMutex
+
+	// mode is the current kcov mode.
+	mode uint8
+
+	// size is the size of the mapping through which the kernel conveys coverage
+	// information to userspace.
+	size uint64
+
+	// owningTask is the task that currently owns coverage data on the system. The
+	// interface for kcov essentially requires that coverage is only going to a
+	// single task. Note that kcov should only generate coverage data for the
+	// owning task, but we currently generate global coverage.
+	owningTask *Task
+
+	// count is a locally cached version of the first uint64 in the kcov data,
+	// which is the number of subsequent entries representing PCs.
+	//
+	// It is used with kcovInode.countBlock(), to copy in/out the first element of
+	// the actual data in an efficient manner, avoid boilerplate, and prevent
+	// accidental garbage escapes by the temporary counts.
+	count uint64
+
+	mappable *mm.SpecialMappable
+}
+
+// NewKcov creates and returns a Kcov instance.
+func (k *Kernel) NewKcov() *Kcov {
+	return &Kcov{
+		mfp: k,
+	}
+}
+
+var coveragePool = sync.Pool{
+	New: func() interface{} {
+		return make([]byte, 0)
+	},
+}
+
+// TaskWork implements TaskWorker.TaskWork.
+func (kcov *Kcov) TaskWork(t *Task) {
+	kcov.mu.Lock()
+	defer kcov.mu.Unlock()
+
+	if kcov.mode != linux.KCOV_MODE_TRACE_PC {
+		return
+	}
+
+	rw := &kcovReadWriter{
+		mf: kcov.mfp.MemoryFile(),
+		fr: kcov.mappable.FileRange(),
+	}
+
+	// Read in the PC count.
+	if _, err := safemem.ReadFullToBlocks(rw, kcov.countBlock()); err != nil {
+		panic(fmt.Sprintf("Internal error reading count from kcov area: %v", err))
+	}
+
+	rw.off = 8 * (1 + kcov.count)
+	n := coverage.ConsumeCoverageData(&kcovIOWriter{rw})
+
+	// Update the pc count, based on the number of entries written. Note that if
+	// we reached the end of the kcov area, we may not have written everything in
+	// output.
+	kcov.count += uint64(n / 8)
+	rw.off = 0
+	if _, err := safemem.WriteFullFromBlocks(rw, kcov.countBlock()); err != nil {
+		panic(fmt.Sprintf("Internal error writing count to kcov area: %v", err))
+	}
+
+	// Re-register for future work.
+	t.RegisterWork(kcov)
+}
+
+// InitTrace performs the KCOV_INIT_TRACE ioctl.
+func (kcov *Kcov) InitTrace(size uint64) error {
+	kcov.mu.Lock()
+	defer kcov.mu.Unlock()
+
+	if kcov.mode != linux.KCOV_MODE_DISABLED {
+		return syserror.EBUSY
+	}
+
+	// To simplify all the logic around mapping, we require that the length of the
+	// shared region is a multiple of the system page size.
+	if (8*size)&(usermem.PageSize-1) != 0 {
+		return syserror.EINVAL
+	}
+
+	// We need space for at least two uint64s to hold current position and a
+	// single PC.
+	if size < 2 || size > kcovAreaSizeMax {
+		return syserror.EINVAL
+	}
+
+	kcov.size = size
+	kcov.mode = linux.KCOV_MODE_INIT
+	return nil
+}
+
+// EnableTrace performs the KCOV_ENABLE_TRACE ioctl.
+func (kcov *Kcov) EnableTrace(ctx context.Context, traceKind uint8) error {
+	t := TaskFromContext(ctx)
+	if t == nil {
+		panic("kcovInode.EnableTrace() cannot be used outside of a task goroutine")
+	}
+
+	kcov.mu.Lock()
+	defer kcov.mu.Unlock()
+
+	// KCOV_ENABLE must be preceded by KCOV_INIT_TRACE and an mmap call.
+	if kcov.mode != linux.KCOV_MODE_INIT || kcov.mappable == nil {
+		return syserror.EINVAL
+	}
+
+	switch traceKind {
+	case linux.KCOV_TRACE_PC:
+		kcov.mode = linux.KCOV_MODE_TRACE_PC
+	case linux.KCOV_TRACE_CMP:
+		// We do not support KCOV_MODE_TRACE_CMP.
+		return syserror.ENOTSUP
+	default:
+		return syserror.EINVAL
+	}
+
+	if kcov.owningTask != nil && kcov.owningTask != t {
+		return syserror.EBUSY
+	}
+
+	kcov.owningTask = t
+	t.SetKcov(kcov)
+	t.RegisterWork(kcov)
+
+	// Clear existing coverage data; the task expects to read only coverage data
+	// from the time it is activated.
+	coverage.ClearCoverageData()
+	return nil
+}
+
+// DisableTrace performs the KCOV_DISABLE_TRACE ioctl.
+func (kcov *Kcov) DisableTrace(ctx context.Context) error {
+	kcov.mu.Lock()
+	defer kcov.mu.Unlock()
+
+	t := TaskFromContext(ctx)
+	if t == nil {
+		panic("kcovInode.EnableTrace() cannot be used outside of a task goroutine")
+	}
+
+	if t != kcov.owningTask {
+		return syserror.EINVAL
+	}
+	kcov.mode = linux.KCOV_MODE_INIT
+	kcov.owningTask = nil
+	if kcov.mappable != nil {
+		kcov.mappable.DecRef(ctx)
+		kcov.mappable = nil
+	}
+	return nil
+}
+
+// Clear resets the mode and clears the owning task and memory mapping for kcov.
+// It is called when the fd corresponding to kcov is closed. Note that the mode
+// needs to be set so that the next call to kcov.TaskWork() will exit early.
+func (kcov *Kcov) Clear(ctx context.Context) {
+	kcov.mu.Lock()
+	kcov.mode = linux.KCOV_MODE_INIT
+	kcov.owningTask = nil
+	if kcov.mappable != nil {
+		kcov.mappable.DecRef(ctx)
+		kcov.mappable = nil
+	}
+	kcov.mu.Unlock()
+}
+
+// OnTaskExit is called when the owning task exits. It is similar to
+// kcov.Clear(), except the memory mapping is not cleared, so that the same
+// mapping can be used in the future if kcov is enabled again by another task.
+func (kcov *Kcov) OnTaskExit() {
+	kcov.mu.Lock()
+	kcov.mode = linux.KCOV_MODE_INIT
+	kcov.owningTask = nil
+	kcov.mu.Unlock()
+}
+
+// ConfigureMMap is called by the vfs.FileDescription for this kcov instance to
+// implement vfs.FileDescription.ConfigureMMap.
+func (kcov *Kcov) ConfigureMMap(ctx context.Context, opts *memmap.MMapOpts) error {
+	kcov.mu.Lock()
+	defer kcov.mu.Unlock()
+
+	if kcov.mode != linux.KCOV_MODE_INIT {
+		return syserror.EINVAL
+	}
+
+	if kcov.mappable == nil {
+		// Set up the kcov area.
+		fr, err := kcov.mfp.MemoryFile().Allocate(kcov.size*8, usage.Anonymous)
+		if err != nil {
+			return err
+		}
+
+		// Get the thread id for the mmap name.
+		t := TaskFromContext(ctx)
+		if t == nil {
+			panic("ThreadFromContext returned nil")
+		}
+		// For convenience, a special mappable is used here. Note that these mappings
+		// will look different under /proc/[pid]/maps than they do on Linux.
+		kcov.mappable = mm.NewSpecialMappable(fmt.Sprintf("[kcov:%d]", t.ThreadID()), kcov.mfp, fr)
+	}
+	kcov.mappable.IncRef()
+	opts.Mappable = kcov.mappable
+	opts.MappingIdentity = kcov.mappable
+	return nil
+}
+
+// kcovReadWriter implements safemem.Reader and safemem.Writer.
+type kcovReadWriter struct {
+	off uint64
+	mf  *pgalloc.MemoryFile
+	fr  memmap.FileRange
+}
+
+// ReadToBlocks implements safemem.Reader.ReadToBlocks.
+func (rw *kcovReadWriter) ReadToBlocks(dsts safemem.BlockSeq) (uint64, error) {
+	if dsts.IsEmpty() {
+		return 0, nil
+	}
+
+	// Limit the read to the kcov range and check for overflow.
+	if rw.fr.Length() <= rw.off {
+		return 0, io.EOF
+	}
+	start := rw.fr.Start + rw.off
+	end := rw.fr.Start + rw.fr.Length()
+	if rend := start + dsts.NumBytes(); rend < end {
+		end = rend
+	}
+
+	// Get internal mappings.
+	bs, err := rw.mf.MapInternal(memmap.FileRange{start, end}, usermem.Read)
+	if err != nil {
+		return 0, err
+	}
+
+	// Copy from internal mappings.
+	n, err := safemem.CopySeq(dsts, bs)
+	rw.off += n
+	return n, err
+}
+
+// WriteFromBlocks implements safemem.Writer.WriteFromBlocks.
+func (rw *kcovReadWriter) WriteFromBlocks(srcs safemem.BlockSeq) (uint64, error) {
+	if srcs.IsEmpty() {
+		return 0, nil
+	}
+
+	// Limit the write to the kcov area and check for overflow.
+	if rw.fr.Length() <= rw.off {
+		return 0, io.EOF
+	}
+	start := rw.fr.Start + rw.off
+	end := rw.fr.Start + rw.fr.Length()
+	if wend := start + srcs.NumBytes(); wend < end {
+		end = wend
+	}
+
+	// Get internal mapping.
+	bs, err := rw.mf.MapInternal(memmap.FileRange{start, end}, usermem.Write)
+	if err != nil {
+		return 0, err
+	}
+
+	// Copy to internal mapping.
+	n, err := safemem.CopySeq(bs, srcs)
+	rw.off += n
+	return n, err
+}
+
+// kcovIOWriter implements io.Writer as a basic wrapper over kcovReadWriter.
+type kcovIOWriter struct {
+	rw *kcovReadWriter
+}
+
+// Write implements io.Writer.Write.
+func (w *kcovIOWriter) Write(p []byte) (int, error) {
+	bs := safemem.BlockSeqOf(safemem.BlockFromSafeSlice(p))
+	n, err := safemem.WriteFullFromBlocks(w.rw, bs)
+	return int(n), err
+}