From f884ea13b713143ff9978092ddb352c159346167 Mon Sep 17 00:00:00 2001 From: Adin Scannell <ascannell@google.com> Date: Tue, 2 Feb 2021 12:01:12 -0800 Subject: Move ring0 package. This allows the package to serve as a general purpose ring0 support package, as opposed to being bound to specific sentry platforms. Updates #5039 PiperOrigin-RevId: 355220044 --- pkg/ring0/pagetables/walker_generic.go | 110 +++++++++++++++++++++++++++++++++ 1 file changed, 110 insertions(+) create mode 100644 pkg/ring0/pagetables/walker_generic.go (limited to 'pkg/ring0/pagetables/walker_generic.go') diff --git a/pkg/ring0/pagetables/walker_generic.go b/pkg/ring0/pagetables/walker_generic.go new file mode 100644 index 000000000..34fba7b84 --- /dev/null +++ b/pkg/ring0/pagetables/walker_generic.go @@ -0,0 +1,110 @@ +// 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 pagetables + +// Visitor is a generic type. +type Visitor interface { + // visit is called on each PTE. The returned boolean indicates whether + // the walk should continue. + visit(start uintptr, pte *PTE, align uintptr) bool + + // requiresAlloc indicates that new entries should be allocated within + // the walked range. + requiresAlloc() bool + + // requiresSplit indicates that entries in the given range should be + // split if they are huge or jumbo pages. + requiresSplit() bool +} + +// Walker walks page tables. +type Walker struct { + // pageTables are the tables to walk. + pageTables *PageTables + + // Visitor is the set of arguments. + visitor Visitor +} + +// iterateRange iterates over all appropriate levels of page tables for the given range. +// +// If requiresAlloc is true, then Set _must_ be called on all given PTEs. The +// exception is super pages. If a valid super page (huge or jumbo) cannot be +// installed, then the walk will continue to individual entries. +// +// This algorithm will attempt to maximize the use of super/sect pages whenever +// possible. Whether a super page is provided will be clear through the range +// provided in the callback. +// +// Note that if requiresAlloc is true, then no gaps will be present. However, +// if alloc is not set, then the iteration will likely be full of gaps. +// +// Note that this function should generally be avoided in favor of Map, Unmap, +// etc. when not necessary. +// +// Precondition: start must be page-aligned. +// Precondition: start must be less than end. +// Precondition: If requiresAlloc is true, then start and end should not span +// non-canonical ranges. If they do, a panic will result. +// +//go:nosplit +func (w *Walker) iterateRange(start, end uintptr) { + if start%pteSize != 0 { + panic("unaligned start") + } + if end < start { + panic("start > end") + } + if start < lowerTop { + if end <= lowerTop { + w.iterateRangeCanonical(start, end) + } else if end > lowerTop && end <= upperBottom { + if w.visitor.requiresAlloc() { + panic("alloc spans non-canonical range") + } + w.iterateRangeCanonical(start, lowerTop) + } else { + if w.visitor.requiresAlloc() { + panic("alloc spans non-canonical range") + } + if !w.iterateRangeCanonical(start, lowerTop) { + return + } + w.iterateRangeCanonical(upperBottom, end) + } + } else if start < upperBottom { + if end <= upperBottom { + if w.visitor.requiresAlloc() { + panic("alloc spans non-canonical range") + } + } else { + if w.visitor.requiresAlloc() { + panic("alloc spans non-canonical range") + } + w.iterateRangeCanonical(upperBottom, end) + } + } else { + w.iterateRangeCanonical(start, end) + } +} + +// next returns the next address quantized by the given size. +// +//go:nosplit +func next(start uintptr, size uintptr) uintptr { + start &= ^(size - 1) + start += size + return start +} -- cgit v1.2.3