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// Copyright 2018 Google LLC
//
// 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.
// +build i386 amd64
package pagetables
import (
"sync/atomic"
"gvisor.googlesource.com/gvisor/pkg/sentry/usermem"
)
// archPageTables is architecture-specific data.
type archPageTables struct {
// pcid is the value assigned by PCIDs.Assign.
//
// Note that zero is a valid PCID.
pcid uint16
}
// CR3 returns the CR3 value for these tables.
//
// This may be called in interrupt contexts. A PCID of zero always implies a
// flush and should be passed when PCIDs are not enabled. See pcids_x86.go for
// more information.
//
//go:nosplit
func (p *PageTables) CR3(noFlush bool, pcid uint16) uint64 {
// Bit 63 is set to avoid flushing the PCID (per SDM 4.10.4.1).
const noFlushBit uint64 = 0x8000000000000000
if noFlush && pcid != 0 {
return noFlushBit | uint64(p.rootPhysical) | uint64(pcid)
}
return uint64(p.rootPhysical) | uint64(pcid)
}
// Bits in page table entries.
const (
present = 0x001
writable = 0x002
user = 0x004
writeThrough = 0x008
cacheDisable = 0x010
accessed = 0x020
dirty = 0x040
super = 0x080
global = 0x100
optionMask = executeDisable | 0xfff
)
// MapOpts are x86 options.
type MapOpts struct {
// AccessType defines permissions.
AccessType usermem.AccessType
// Global indicates the page is globally accessible.
Global bool
// User indicates the page is a user page.
User bool
}
// PTE is a page table entry.
type PTE uintptr
// Clear clears this PTE, including super page information.
//
//go:nosplit
func (p *PTE) Clear() {
atomic.StoreUintptr((*uintptr)(p), 0)
}
// Valid returns true iff this entry is valid.
//
//go:nosplit
func (p *PTE) Valid() bool {
return atomic.LoadUintptr((*uintptr)(p))&present != 0
}
// Opts returns the PTE options.
//
// These are all options except Valid and Super.
//
//go:nosplit
func (p *PTE) Opts() MapOpts {
v := atomic.LoadUintptr((*uintptr)(p))
return MapOpts{
AccessType: usermem.AccessType{
Read: v&present != 0,
Write: v&writable != 0,
Execute: v&executeDisable == 0,
},
Global: v&global != 0,
User: v&user != 0,
}
}
// SetSuper sets this page as a super page.
//
// The page must not be valid or a panic will result.
//
//go:nosplit
func (p *PTE) SetSuper() {
if p.Valid() {
// This is not allowed.
panic("SetSuper called on valid page!")
}
atomic.StoreUintptr((*uintptr)(p), super)
}
// IsSuper returns true iff this page is a super page.
//
//go:nosplit
func (p *PTE) IsSuper() bool {
return atomic.LoadUintptr((*uintptr)(p))&super != 0
}
// Set sets this PTE value.
//
// This does not change the super page property.
//
//go:nosplit
func (p *PTE) Set(addr uintptr, opts MapOpts) {
if !opts.AccessType.Any() {
p.Clear()
return
}
v := (addr &^ optionMask) | present | accessed
if opts.User {
v |= user
}
if opts.Global {
v |= global
}
if !opts.AccessType.Execute {
v |= executeDisable
}
if opts.AccessType.Write {
v |= writable | dirty
}
if p.IsSuper() {
// Note that this is inherited from the previous instance. Set
// does not change the value of Super. See above.
v |= super
}
atomic.StoreUintptr((*uintptr)(p), v)
}
// setPageTable sets this PTE value and forces the write bit and super bit to
// be cleared. This is used explicitly for breaking super pages.
//
//go:nosplit
func (p *PTE) setPageTable(pt *PageTables, ptes *PTEs) {
addr := pt.Allocator.PhysicalFor(ptes)
if addr&^optionMask != addr {
// This should never happen.
panic("unaligned physical address!")
}
v := addr | present | user | writable | accessed | dirty
atomic.StoreUintptr((*uintptr)(p), v)
}
// Address extracts the address. This should only be used if Valid returns true.
//
//go:nosplit
func (p *PTE) Address() uintptr {
return atomic.LoadUintptr((*uintptr)(p)) &^ optionMask
}
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