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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 kvm
import (
"fmt"
"golang.org/x/sys/unix"
"gvisor.dev/gvisor/pkg/ring0"
"gvisor.dev/gvisor/pkg/sentry/arch"
"gvisor.dev/gvisor/pkg/sighandling"
)
// bluepill enters guest mode.
func bluepill(*vCPU)
// sighandler is the signal entry point.
func sighandler()
// dieTrampoline is the assembly trampoline. This calls dieHandler.
//
// This uses an architecture-specific calling convention, documented in
// dieArchSetup and the assembly implementation for dieTrampoline.
func dieTrampoline()
// Return the start address of the functions above.
//
// In Go 1.17+, Go references to assembly functions resolve to an ABIInternal
// wrapper function rather than the function itself. We must reference from
// assembly to get the ABI0 (i.e., primary) address.
func addrOfSighandler() uintptr
func addrOfDieTrampoline() uintptr
var (
// bounceSignal is the signal used for bouncing KVM.
//
// We use SIGCHLD because it is not masked by the runtime, and
// it will be ignored properly by other parts of the kernel.
bounceSignal = unix.SIGCHLD
// bounceSignalMask has only bounceSignal set.
bounceSignalMask = uint64(1 << (uint64(bounceSignal) - 1))
// bounce is the interrupt vector used to return to the kernel.
bounce = uint32(ring0.VirtualizationException)
// savedHandler is a pointer to the previous handler.
//
// This is called by bluepillHandler.
savedHandler uintptr
// savedSigsysHandler is a pointer to the previos handler of the SIGSYS signals.
savedSigsysHandler uintptr
// dieTrampolineAddr is the address of dieTrampoline.
dieTrampolineAddr uintptr
)
// _SYS_KVM_RETURN_TO_HOST is the system call that is used to transition
// to host.
const _SYS_KVM_RETURN_TO_HOST = ^uintptr(0)
// redpill invokes a syscall with -1.
//
//go:nosplit
func redpill() {
unix.RawSyscall(_SYS_KVM_RETURN_TO_HOST, 0, 0, 0)
}
// dieHandler is called by dieTrampoline.
//
//go:nosplit
func dieHandler(c *vCPU) {
throw(c.dieState.message)
}
// die is called to set the vCPU up to panic.
//
// This loads vCPU state, and sets up a call for the trampoline.
//
//go:nosplit
func (c *vCPU) die(context *arch.SignalContext64, msg string) {
// Save the death message, which will be thrown.
c.dieState.message = msg
// Setup the trampoline.
dieArchSetup(c, context, &c.dieState.guestRegs)
}
func init() {
// Install the handler.
if err := sighandling.ReplaceSignalHandler(bluepillSignal, addrOfSighandler(), &savedHandler); err != nil {
panic(fmt.Sprintf("Unable to set handler for signal %d: %v", bluepillSignal, err))
}
// Extract the address for the trampoline.
dieTrampolineAddr = addrOfDieTrampoline()
}
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