visor/pkg/sentry/platform/kvm/virtual_map.go

// 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 kvm

import (
	"bufio"
	"fmt"
	"io"
	"os"
	"regexp"
	"strconv"
	"strings"

	"gvisor.dev/gvisor/pkg/hostarch"
)

type virtualRegion struct {
	region
	accessType hostarch.AccessType
	shared     bool
	offset     uintptr
	filename   string
}

// mapsLine matches a single line from /proc/PID/maps.
var mapsLine = regexp.MustCompile(`([0-9a-f]+)-([0-9a-f]+) ([r-][w-][x-][sp]) ([0-9a-f]+) [0-9a-f]{2,3}:[0-9a-f]{2,} [0-9]+\s+(.*)`)

var excludeVvarRegion bool

// excludeVirtualRegion returns true if these regions should be excluded from
// the physical map. Virtual regions need to be excluded if get_user_pages will
// fail on those addresses, preventing KVM from satisfying EPT faults.
//
// This is called by the physical map functions, not applyVirtualRegions.
func excludeVirtualRegion(r virtualRegion) bool {
	return excludeVvarRegion && (strings.HasPrefix(r.filename, "[vvar") || strings.HasPrefix(r.filename, "[vdso"))
}

// mmioVirtualRegion returns true if r should be included in the physical map,
// but not actually mapped in the physical address space. This ensures that
// accesses to this region cause MMIO exits.
//
// This is called by the physical map functions, not applyVirtualRegions.
func mmioVirtualRegion(r virtualRegion) bool {
	return r.virtual == ioeventfdMMIO.mapping
}

// applyVirtualRegions parses the process maps file.
//
// Takes a function that's called on each virtualRegion. If function returns
// true, stops iteration.
//
// Unlike mappedRegions, these are not consistent over time.
func applyVirtualRegions(fn func(vr virtualRegion) bool) error {
	// Open /proc/self/maps.
	f, err := os.Open("/proc/self/maps")
	if err != nil {
		return err
	}
	defer f.Close()

	// Parse all entries.
	r := bufio.NewReader(f)
	for {
		b, err := r.ReadBytes('\n')
		if len(b) > 0 {
			m := mapsLine.FindSubmatch(b)
			if m == nil {
				// This should not happen: kernel bug?
				return fmt.Errorf("badly formed line: %v", string(b))
			}
			start, err := strconv.ParseUint(string(m[1]), 16, 64)
			if err != nil {
				return fmt.Errorf("bad start address: %v", string(b))
			}
			end, err := strconv.ParseUint(string(m[2]), 16, 64)
			if err != nil {
				return fmt.Errorf("bad end address: %v", string(b))
			}
			read := m[3][0] == 'r'
			write := m[3][1] == 'w'
			execute := m[3][2] == 'x'
			shared := m[3][3] == 's'
			offset, err := strconv.ParseUint(string(m[4]), 16, 64)
			if err != nil {
				return fmt.Errorf("bad offset: %v", string(b))
			}
			if stop := fn(virtualRegion{
				region: region{
					virtual: uintptr(start),
					length:  uintptr(end - start),
				},
				accessType: hostarch.AccessType{
					Read:    read,
					Write:   write,
					Execute: execute,
				},
				shared:   shared,
				offset:   uintptr(offset),
				filename: string(m[5]),
			}); stop {
				break
			}
		}
		if err != nil && err == io.EOF {
			break
		} else if err != nil {
			return err
		}
	}

	return nil
}

func findRegionStartingWith(name string) (region, error) {
	var r region
	var found bool
	err := applyVirtualRegions(func(vr virtualRegion) bool {
		if strings.HasPrefix(vr.filename, name) {
			r = vr.region
			found = true
			return true
		}
		return false
	})
	if err != nil {
		return region{}, err
	}
	if !found {
		return region{}, fmt.Errorf("region %s not found", name)
	}
	return r, nil
}