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// Copyright 2018 Google Inc.
//
// 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 kvm
import (
"syscall"
"gvisor.googlesource.com/gvisor/pkg/sentry/arch"
"gvisor.googlesource.com/gvisor/pkg/sentry/platform/ring0"
)
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 = syscall.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)
)
// redpill on amd64 invokes a syscall with -1.
//
//go:nosplit
func redpill() {
syscall.RawSyscall(^uintptr(0), 0, 0, 0)
}
// bluepillArchEnter is called during bluepillEnter.
//
//go:nosplit
func bluepillArchEnter(context *arch.SignalContext64) (c *vCPU) {
c = vCPUPtr(uintptr(context.Rax))
regs := c.CPU.Registers()
regs.R8 = context.R8
regs.R9 = context.R9
regs.R10 = context.R10
regs.R11 = context.R11
regs.R12 = context.R12
regs.R13 = context.R13
regs.R14 = context.R14
regs.R15 = context.R15
regs.Rdi = context.Rdi
regs.Rsi = context.Rsi
regs.Rbp = context.Rbp
regs.Rbx = context.Rbx
regs.Rdx = context.Rdx
regs.Rax = context.Rax
regs.Rcx = context.Rcx
regs.Rsp = context.Rsp
regs.Rip = context.Rip
regs.Eflags = context.Eflags
regs.Eflags &^= uint64(ring0.KernelFlagsClear)
regs.Eflags |= ring0.KernelFlagsSet
regs.Cs = uint64(ring0.Kcode)
regs.Ds = uint64(ring0.Udata)
regs.Es = uint64(ring0.Udata)
regs.Fs = uint64(ring0.Udata)
regs.Ss = uint64(ring0.Kdata)
// ring0 uses GS exclusively, so we use GS_base to store the location
// of the floating point address.
//
// The address will be restored directly after running the VCPU, and
// will be saved again prior to halting. We rely on the fact that the
// SaveFloatingPointer/LoadFloatingPoint functions use the most
// efficient mechanism available (including compression) so the state
// size is guaranteed to be less than what's pointed to here.
regs.Gs_base = uint64(context.Fpstate)
return
}
// bluepillSyscall handles kernel syscalls.
//
//go:nosplit
func bluepillSyscall() {
regs := ring0.Current().Registers()
if regs.Rax != ^uint64(0) {
regs.Rip -= 2 // Rewind.
}
ring0.SaveFloatingPoint(bytePtr(uintptr(regs.Gs_base)))
ring0.Halt()
ring0.LoadFloatingPoint(bytePtr(uintptr(regs.Gs_base)))
}
// bluepillException handles kernel exceptions.
//
//go:nosplit
func bluepillException(vector ring0.Vector) {
regs := ring0.Current().Registers()
if vector == ring0.Vector(bounce) {
// These should not interrupt kernel execution; point the Rip
// to zero to ensure that we get a reasonable panic when we
// attempt to return.
regs.Rip = 0
}
ring0.SaveFloatingPoint(bytePtr(uintptr(regs.Gs_base)))
ring0.Halt()
ring0.LoadFloatingPoint(bytePtr(uintptr(regs.Gs_base)))
}
// bluepillArchExit is called during bluepillEnter.
//
//go:nosplit
func bluepillArchExit(c *vCPU, context *arch.SignalContext64) {
regs := c.CPU.Registers()
context.R8 = regs.R8
context.R9 = regs.R9
context.R10 = regs.R10
context.R11 = regs.R11
context.R12 = regs.R12
context.R13 = regs.R13
context.R14 = regs.R14
context.R15 = regs.R15
context.Rdi = regs.Rdi
context.Rsi = regs.Rsi
context.Rbp = regs.Rbp
context.Rbx = regs.Rbx
context.Rdx = regs.Rdx
context.Rax = regs.Rax
context.Rcx = regs.Rcx
context.Rsp = regs.Rsp
context.Rip = regs.Rip
context.Eflags = regs.Eflags
}
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