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

1 files changed, 161 insertions, 0 deletions

diff --git a/pkg/ring0/defs_amd64.go b/pkg/ring0/defs_amd64.go
new file mode 100644
index 000000000..ceddf719d
--- /dev/null
+++ b/pkg/ring0/defs_amd64.go
@@ -0,0 +1,161 @@
+// 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.
+
+// +build amd64
+
+package ring0
+
+import (
+	"gvisor.dev/gvisor/pkg/usermem"
+)
+
+var (
+	// UserspaceSize is the total size of userspace.
+	UserspaceSize = uintptr(1) << (VirtualAddressBits() - 1)
+
+	// MaximumUserAddress is the largest possible user address.
+	MaximumUserAddress = (UserspaceSize - 1) & ^uintptr(usermem.PageSize-1)
+
+	// KernelStartAddress is the starting kernel address.
+	KernelStartAddress = ^uintptr(0) - (UserspaceSize - 1)
+)
+
+// Segment indices and Selectors.
+const (
+	// Index into GDT array.
+	_          = iota // Null descriptor first.
+	_                 // Reserved (Linux is kernel 32).
+	segKcode          // Kernel code (64-bit).
+	segKdata          // Kernel data.
+	segUcode32        // User code (32-bit).
+	segUdata          // User data.
+	segUcode64        // User code (64-bit).
+	segTss            // Task segment descriptor.
+	segTssHi          // Upper bits for TSS.
+	segLast           // Last segment (terminal, not included).
+)
+
+// Selectors.
+const (
+	Kcode   Selector = segKcode << 3
+	Kdata   Selector = segKdata << 3
+	Ucode32 Selector = (segUcode32 << 3) | 3
+	Udata   Selector = (segUdata << 3) | 3
+	Ucode64 Selector = (segUcode64 << 3) | 3
+	Tss     Selector = segTss << 3
+)
+
+// Standard segments.
+var (
+	UserCodeSegment32 SegmentDescriptor
+	UserDataSegment   SegmentDescriptor
+	UserCodeSegment64 SegmentDescriptor
+	KernelCodeSegment SegmentDescriptor
+	KernelDataSegment SegmentDescriptor
+)
+
+// KernelArchState contains architecture-specific state.
+type KernelArchState struct {
+	// cpuEntries is array of kernelEntry for all cpus.
+	cpuEntries []kernelEntry
+
+	// globalIDT is our set of interrupt gates.
+	globalIDT *idt64
+}
+
+// kernelEntry contains minimal CPU-specific arch state
+// that can be mapped at the upper of the address space.
+// Malicious APP might steal info from it via CPU bugs.
+type kernelEntry struct {
+	// stack is the stack used for interrupts on this CPU.
+	stack [256]byte
+
+	// scratch space for temporary usage.
+	scratch0 uint64
+
+	// stackTop is the top of the stack.
+	stackTop uint64
+
+	// cpuSelf is back reference to CPU.
+	cpuSelf *CPU
+
+	// kernelCR3 is the cr3 used for sentry kernel.
+	kernelCR3 uintptr
+
+	// gdt is the CPU's descriptor table.
+	gdt descriptorTable
+
+	// tss is the CPU's task state.
+	tss TaskState64
+}
+
+// CPUArchState contains CPU-specific arch state.
+type CPUArchState struct {
+	// errorCode is the error code from the last exception.
+	errorCode uintptr
+
+	// errorType indicates the type of error code here, it is always set
+	// along with the errorCode value above.
+	//
+	// It will either by 1, which indicates a user error, or 0 indicating a
+	// kernel error. If the error code below returns false (kernel error),
+	// then it cannot provide relevant information about the last
+	// exception.
+	errorType uintptr
+
+	*kernelEntry
+}
+
+// ErrorCode returns the last error code.
+//
+// The returned boolean indicates whether the error code corresponds to the
+// last user error or not. If it does not, then fault information must be
+// ignored. This is generally the result of a kernel fault while servicing a
+// user fault.
+//
+//go:nosplit
+func (c *CPU) ErrorCode() (value uintptr, user bool) {
+	return c.errorCode, c.errorType != 0
+}
+
+// ClearErrorCode resets the error code.
+//
+//go:nosplit
+func (c *CPU) ClearErrorCode() {
+	c.errorCode = 0 // No code.
+	c.errorType = 1 // User mode.
+}
+
+// SwitchArchOpts are embedded in SwitchOpts.
+type SwitchArchOpts struct {
+	// UserPCID indicates that the application PCID to be used on switch,
+	// assuming that PCIDs are supported.
+	//
+	// Per pagetables_x86.go, a zero PCID implies a flush.
+	UserPCID uint16
+
+	// KernelPCID indicates that the kernel PCID to be used on return,
+	// assuming that PCIDs are supported.
+	//
+	// Per pagetables_x86.go, a zero PCID implies a flush.
+	KernelPCID uint16
+}
+
+func init() {
+	KernelCodeSegment.setCode64(0, 0, 0)
+	KernelDataSegment.setData(0, 0xffffffff, 0)
+	UserCodeSegment32.setCode64(0, 0, 3)
+	UserDataSegment.setData(0, 0xffffffff, 3)
+	UserCodeSegment64.setCode64(0, 0, 3)
+}