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/allocator_unsafe.go | 53 ++++++++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)
 create mode 100644 pkg/ring0/pagetables/allocator_unsafe.go

(limited to 'pkg/ring0/pagetables/allocator_unsafe.go')

diff --git a/pkg/ring0/pagetables/allocator_unsafe.go b/pkg/ring0/pagetables/allocator_unsafe.go
new file mode 100644
index 000000000..d08bfdeb3
--- /dev/null
+++ b/pkg/ring0/pagetables/allocator_unsafe.go
@@ -0,0 +1,53 @@
+// 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
+
+import (
+	"unsafe"
+
+	"gvisor.dev/gvisor/pkg/usermem"
+)
+
+// newAlignedPTEs returns a set of aligned PTEs.
+func newAlignedPTEs() *PTEs {
+	ptes := new(PTEs)
+	offset := physicalFor(ptes) & (usermem.PageSize - 1)
+	if offset == 0 {
+		// Already aligned.
+		return ptes
+	}
+
+	// Need to force an aligned allocation.
+	unaligned := make([]byte, (2*usermem.PageSize)-1)
+	offset = uintptr(unsafe.Pointer(&unaligned[0])) & (usermem.PageSize - 1)
+	if offset != 0 {
+		offset = usermem.PageSize - offset
+	}
+	return (*PTEs)(unsafe.Pointer(&unaligned[offset]))
+}
+
+// physicalFor returns the "physical" address for PTEs.
+//
+//go:nosplit
+func physicalFor(ptes *PTEs) uintptr {
+	return uintptr(unsafe.Pointer(ptes))
+}
+
+// fromPhysical returns the PTEs from the "physical" address.
+//
+//go:nosplit
+func fromPhysical(physical uintptr) *PTEs {
+	return (*PTEs)(unsafe.Pointer(physical))
+}
-- 
cgit v1.2.3