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// 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 usermem
import (
"syscall"
)
// AccessType specifies memory access types. This is used for
// setting mapping permissions, as well as communicating faults.
//
// +stateify savable
type AccessType struct {
// Read is read access.
Read bool
// Write is write access.
Write bool
// Execute is executable access.
Execute bool
}
// String returns a pretty representation of access. This looks like the
// familiar r-x, rw-, etc. and can be relied on as such.
func (a AccessType) String() string {
bits := [3]byte{'-', '-', '-'}
if a.Read {
bits[0] = 'r'
}
if a.Write {
bits[1] = 'w'
}
if a.Execute {
bits[2] = 'x'
}
return string(bits[:])
}
// Any returns true iff at least one of Read, Write or Execute is true.
func (a AccessType) Any() bool {
return a.Read || a.Write || a.Execute
}
// Prot returns the system prot (syscall.PROT_READ, etc.) for this access.
func (a AccessType) Prot() int {
var prot int
if a.Read {
prot |= syscall.PROT_READ
}
if a.Write {
prot |= syscall.PROT_WRITE
}
if a.Execute {
prot |= syscall.PROT_EXEC
}
return prot
}
// SupersetOf returns true iff the access types in a are a superset of the
// access types in other.
func (a AccessType) SupersetOf(other AccessType) bool {
if !a.Read && other.Read {
return false
}
if !a.Write && other.Write {
return false
}
if !a.Execute && other.Execute {
return false
}
return true
}
// Intersect returns the access types set in both a and other.
func (a AccessType) Intersect(other AccessType) AccessType {
return AccessType{
Read: a.Read && other.Read,
Write: a.Write && other.Write,
Execute: a.Execute && other.Execute,
}
}
// Union returns the access types set in either a or other.
func (a AccessType) Union(other AccessType) AccessType {
return AccessType{
Read: a.Read || other.Read,
Write: a.Write || other.Write,
Execute: a.Execute || other.Execute,
}
}
// Effective returns the set of effective access types allowed by a, even if
// some types are not explicitly allowed.
func (a AccessType) Effective() AccessType {
// In Linux, Write and Execute access generally imply Read access. See
// mm/mmap.c:protection_map.
//
// The notable exception is get_user_pages, which only checks against
// the original vma flags. That said, most user memory accesses do not
// use GUP.
if a.Write || a.Execute {
a.Read = true
}
return a
}
// Convenient access types.
var (
NoAccess = AccessType{}
Read = AccessType{Read: true}
Write = AccessType{Write: true}
Execute = AccessType{Execute: true}
ReadWrite = AccessType{Read: true, Write: true}
AnyAccess = AccessType{Read: true, Write: true, Execute: true}
)
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