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// Copyright 2019 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.
// +build arm64
package pagetables
import (
"sync/atomic"
"gvisor.dev/gvisor/pkg/usermem"
)
// archPageTables is architecture-specific data.
type archPageTables struct {
// root is the pagetable root for kernel space.
root *PTEs
// rootPhysical is the cached physical address of the root.
//
// This is saved only to prevent constant translation.
rootPhysical uintptr
asid uint16
}
// TTBR0_EL1 returns the translation table base register 0.
//
//go:nosplit
func (p *PageTables) TTBR0_EL1(noFlush bool, asid uint16) uint64 {
return uint64(p.rootPhysical) | (uint64(asid)&ttbrASIDMask)<<ttbrASIDOffset
}
// TTBR1_EL1 returns the translation table base register 1.
//
//go:nosplit
func (p *PageTables) TTBR1_EL1(noFlush bool, asid uint16) uint64 {
return uint64(p.archPageTables.rootPhysical) | (uint64(asid)&ttbrASIDMask)<<ttbrASIDOffset
}
// Bits in page table entries.
const (
typeTable = 0x3 << 0
typeSect = 0x1 << 0
typePage = 0x3 << 0
pteValid = 0x1 << 0
pteTableBit = 0x1 << 1
pteTypeMask = 0x3 << 0
present = pteValid | pteTableBit
user = 0x1 << 6 /* AP[1] */
readOnly = 0x1 << 7 /* AP[2] */
accessed = 0x1 << 10
dbm = 0x1 << 51
writable = dbm
cont = 0x1 << 52
pxn = 0x1 << 53
xn = 0x1 << 54
dirty = 0x1 << 55
nG = 0x1 << 11
shared = 0x3 << 8
)
const (
mtNormal = 0x4 << 2
)
const (
executeDisable = xn
optionMask = 0xfff | 0xfff<<48
protDefault = accessed | shared | mtNormal
)
// 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 sect 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 Sect.
//
//go:nosplit
func (p *PTE) Opts() MapOpts {
v := atomic.LoadUintptr((*uintptr)(p))
return MapOpts{
AccessType: usermem.AccessType{
Read: true,
Write: v&readOnly == 0,
Execute: v&xn == 0,
},
Global: v&nG == 0,
User: v&user != 0,
}
}
// SetSect sets this page as a sect page.
//
// The page must not be valid or a panic will result.
//
//go:nosplit
func (p *PTE) SetSect() {
if p.Valid() {
// This is not allowed.
panic("SetSect called on valid page!")
}
atomic.StoreUintptr((*uintptr)(p), typeSect)
}
// IsSect returns true iff this page is a sect page.
//
//go:nosplit
func (p *PTE) IsSect() bool {
return atomic.LoadUintptr((*uintptr)(p))&pteTypeMask == typeSect
}
// Set sets this PTE value.
//
// This does not change the sect page property.
//
//go:nosplit
func (p *PTE) Set(addr uintptr, opts MapOpts) {
if !opts.AccessType.Any() {
p.Clear()
return
}
v := (addr &^ optionMask) | protDefault | nG | readOnly
if p.IsSect() {
// Note that this is inherited from the previous instance. Set
// does not change the value of Sect. See above.
v |= typeSect
} else {
v |= typePage
}
if opts.Global {
v = v &^ nG
}
if opts.AccessType.Execute {
v = v &^ executeDisable
} else {
v |= executeDisable
}
if opts.AccessType.Write {
v = v &^ readOnly
}
if opts.User {
v |= user
} else {
v = v &^ user
}
atomic.StoreUintptr((*uintptr)(p), v)
}
// setPageTable sets this PTE value and forces the write bit and sect bit to
// be cleared. This is used explicitly for breaking sect 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 | typeTable | protDefault
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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