2018-04-27 17:37:02 +00:00
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// Copyright 2018 Google Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// +build amd64
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package kvm
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import (
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"fmt"
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"reflect"
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"syscall"
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"gvisor.googlesource.com/gvisor/pkg/sentry/arch"
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"gvisor.googlesource.com/gvisor/pkg/sentry/platform"
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"gvisor.googlesource.com/gvisor/pkg/sentry/platform/ring0"
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2018-06-07 05:51:58 +00:00
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"gvisor.googlesource.com/gvisor/pkg/sentry/platform/ring0/pagetables"
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2018-04-27 17:37:02 +00:00
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"gvisor.googlesource.com/gvisor/pkg/sentry/usermem"
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)
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// initArchState initializes architecture-specific state.
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func (m *machine) initArchState(vCPUs int) error {
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// Set the legacy TSS address. This address is covered by the reserved
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// range (up to 4GB). In fact, this is a main reason it exists.
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if _, _, errno := syscall.RawSyscall(
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syscall.SYS_IOCTL,
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uintptr(m.fd),
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_KVM_SET_TSS_ADDR,
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uintptr(reservedMemory-(3*usermem.PageSize))); errno != 0 {
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return errno
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}
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return nil
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}
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2018-06-07 05:51:58 +00:00
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type vCPUArchState struct {
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// PCIDs is the set of PCIDs for this vCPU.
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//
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// This starts above fixedKernelPCID.
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PCIDs *pagetables.PCIDs
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}
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const (
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// fixedKernelPCID is a fixed kernel PCID used for the kernel page
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// tables. We must start allocating user PCIDs above this in order to
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// avoid any conflict (see below).
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fixedKernelPCID = 1
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// poolPCIDs is the number of PCIDs to record in the database. As this
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// grows, assignment can take longer, since it is a simple linear scan.
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// Beyond a relatively small number, there are likely few perform
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// benefits, since the TLB has likely long since lost any translations
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// from more than a few PCIDs past.
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poolPCIDs = 8
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)
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// dropPageTables drops cached page table entries.
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func (m *machine) dropPageTables(pt *pagetables.PageTables) {
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m.mu.Lock()
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defer m.mu.Unlock()
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// Clear from all PCIDs.
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for _, c := range m.vCPUs {
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c.PCIDs.Drop(pt)
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}
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}
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2018-04-27 17:37:02 +00:00
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// initArchState initializes architecture-specific state.
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func (c *vCPU) initArchState() error {
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var (
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kernelSystemRegs systemRegs
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kernelUserRegs userRegs
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)
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// Set base control registers.
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kernelSystemRegs.CR0 = c.CR0()
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kernelSystemRegs.CR4 = c.CR4()
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kernelSystemRegs.EFER = c.EFER()
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// Set the IDT & GDT in the registers.
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kernelSystemRegs.IDT.base, kernelSystemRegs.IDT.limit = c.IDT()
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kernelSystemRegs.GDT.base, kernelSystemRegs.GDT.limit = c.GDT()
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kernelSystemRegs.CS.Load(&ring0.KernelCodeSegment, ring0.Kcode)
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kernelSystemRegs.DS.Load(&ring0.UserDataSegment, ring0.Udata)
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kernelSystemRegs.ES.Load(&ring0.UserDataSegment, ring0.Udata)
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kernelSystemRegs.SS.Load(&ring0.KernelDataSegment, ring0.Kdata)
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kernelSystemRegs.FS.Load(&ring0.UserDataSegment, ring0.Udata)
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kernelSystemRegs.GS.Load(&ring0.UserDataSegment, ring0.Udata)
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tssBase, tssLimit, tss := c.TSS()
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kernelSystemRegs.TR.Load(tss, ring0.Tss)
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kernelSystemRegs.TR.base = tssBase
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kernelSystemRegs.TR.limit = uint32(tssLimit)
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2018-06-07 05:51:58 +00:00
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// Point to kernel page tables, with no initial PCID.
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kernelSystemRegs.CR3 = c.machine.kernel.PageTables.CR3(false, 0)
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// Initialize the PCID database.
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if hasGuestPCID {
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// Note that NewPCIDs may return a nil table here, in which
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// case we simply don't use PCID support (see below). In
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// practice, this should not happen, however.
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c.PCIDs = pagetables.NewPCIDs(fixedKernelPCID+1, poolPCIDs)
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}
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2018-04-27 17:37:02 +00:00
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// Set the CPUID; this is required before setting system registers,
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// since KVM will reject several CR4 bits if the CPUID does not
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// indicate the support is available.
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if err := c.setCPUID(); err != nil {
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return err
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}
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// Set the entrypoint for the kernel.
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kernelUserRegs.RIP = uint64(reflect.ValueOf(ring0.Start).Pointer())
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kernelUserRegs.RAX = uint64(reflect.ValueOf(&c.CPU).Pointer())
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kernelUserRegs.RFLAGS = ring0.KernelFlagsSet
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// Set the system registers.
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if err := c.setSystemRegisters(&kernelSystemRegs); err != nil {
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return err
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}
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// Set the user registers.
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if err := c.setUserRegisters(&kernelUserRegs); err != nil {
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return err
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}
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// Set the time offset to the host native time.
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return c.setSystemTime()
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}
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2018-05-16 05:43:52 +00:00
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// fault generates an appropriate fault return.
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//
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//go:nosplit
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func (c *vCPU) fault(signal int32) (*arch.SignalInfo, usermem.AccessType, error) {
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bluepill(c) // Probably no-op, but may not be.
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faultAddr := ring0.ReadCR2()
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code, user := c.ErrorCode()
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if !user {
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// The last fault serviced by this CPU was not a user
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// fault, so we can't reliably trust the faultAddr or
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// the code provided here. We need to re-execute.
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return nil, usermem.NoAccess, platform.ErrContextInterrupt
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}
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info := &arch.SignalInfo{Signo: signal}
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info.SetAddr(uint64(faultAddr))
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accessType := usermem.AccessType{
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Read: code&(1<<1) == 0,
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Write: code&(1<<1) != 0,
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Execute: code&(1<<4) != 0,
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}
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return info, accessType, platform.ErrContextSignal
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}
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2018-04-27 17:37:02 +00:00
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// SwitchToUser unpacks architectural-details.
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2018-05-30 22:13:36 +00:00
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func (c *vCPU) SwitchToUser(switchOpts ring0.SwitchOpts) (*arch.SignalInfo, usermem.AccessType, error) {
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// Assign PCIDs.
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if c.PCIDs != nil {
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var requireFlushPCID bool // Force a flush?
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switchOpts.UserPCID, requireFlushPCID = c.PCIDs.Assign(switchOpts.PageTables)
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switchOpts.KernelPCID = fixedKernelPCID
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switchOpts.Flush = switchOpts.Flush || requireFlushPCID
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}
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2018-04-27 17:37:02 +00:00
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// See below.
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var vector ring0.Vector
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// Past this point, stack growth can cause system calls (and a break
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// from guest mode). So we need to ensure that between the bluepill
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// call here and the switch call immediately below, no additional
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// allocations occur.
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entersyscall()
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bluepill(c)
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vector = c.CPU.SwitchToUser(switchOpts)
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2018-04-27 17:37:02 +00:00
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exitsyscall()
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switch vector {
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2018-05-15 04:13:28 +00:00
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case ring0.Syscall, ring0.SyscallInt80:
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// Fast path: system call executed.
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return nil, usermem.NoAccess, nil
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2018-05-16 05:43:52 +00:00
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case ring0.PageFault:
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return c.fault(int32(syscall.SIGSEGV))
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2018-04-27 17:37:02 +00:00
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case ring0.Debug, ring0.Breakpoint:
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info := &arch.SignalInfo{Signo: int32(syscall.SIGTRAP)}
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return info, usermem.AccessType{}, platform.ErrContextSignal
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case ring0.GeneralProtectionFault:
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2018-05-30 22:13:36 +00:00
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if !ring0.IsCanonical(switchOpts.Registers.Rip) {
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2018-04-27 17:37:02 +00:00
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// If the RIP is non-canonical, it's a SEGV.
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info := &arch.SignalInfo{Signo: int32(syscall.SIGSEGV)}
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return info, usermem.AccessType{}, platform.ErrContextSignal
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}
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// Otherwise, we deliver a SIGBUS.
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info := &arch.SignalInfo{Signo: int32(syscall.SIGBUS)}
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return info, usermem.AccessType{}, platform.ErrContextSignal
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case ring0.InvalidOpcode:
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info := &arch.SignalInfo{Signo: int32(syscall.SIGILL)}
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return info, usermem.AccessType{}, platform.ErrContextSignal
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case ring0.X87FloatingPointException:
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info := &arch.SignalInfo{Signo: int32(syscall.SIGFPE)}
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return info, usermem.AccessType{}, platform.ErrContextSignal
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case ring0.Vector(bounce):
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return nil, usermem.NoAccess, platform.ErrContextInterrupt
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2018-05-16 05:43:52 +00:00
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case ring0.NMI:
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// An NMI is generated only when a fault is not servicable by
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// KVM itself, so we think some mapping is writeable but it's
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// really not. This could happen, e.g. if some file is
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// truncated (and would generate a SIGBUS) and we map it
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// directly into the instance.
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return c.fault(int32(syscall.SIGBUS))
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2018-04-27 17:37:02 +00:00
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default:
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panic(fmt.Sprintf("unexpected vector: 0x%x", vector))
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}
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}
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2018-06-07 06:25:26 +00:00
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// retryInGuest runs the given function in guest mode.
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//
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// If the function does not complete in guest mode (due to execution of a
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// system call due to a GC stall, for example), then it will be retried. The
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// given function must be idempotent as a result of the retry mechanism.
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func (m *machine) retryInGuest(fn func()) {
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c := m.Get()
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defer m.Put(c)
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for {
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c.ClearErrorCode() // See below.
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bluepill(c) // Force guest mode.
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fn() // Execute the given function.
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_, user := c.ErrorCode()
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if user {
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// If user is set, then we haven't bailed back to host
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// mode via a kernel exception or system call. We
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// consider the full function to have executed in guest
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// mode and we can return.
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break
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}
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}
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}
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