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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.
//go:build amd64
// +build amd64
package kvm
import (
"golang.org/x/sys/unix"
"gvisor.dev/gvisor/pkg/ring0"
"gvisor.dev/gvisor/pkg/sentry/arch"
)
var (
// The action for bluepillSignal is changed by sigaction().
bluepillSignal = unix.SIGSEGV
)
// bluepillArchEnter is called during bluepillEnter.
//
//go:nosplit
func bluepillArchEnter(context *arch.SignalContext64) *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.Ss = uint64(ring0.Kdata)
return c
}
// KernelSyscall handles kernel syscalls.
//
// +checkescape:all
//
//go:nosplit
func (c *vCPU) KernelSyscall() {
regs := c.Registers()
if regs.Rax != ^uint64(0) {
regs.Rip -= 2 // Rewind.
}
// N.B. Since KernelSyscall is called when the kernel makes a syscall,
// FS_BASE is already set for correct execution of this function.
//
// Refresher on syscall/exception handling:
// 1. When the sentry is in guest mode and makes a syscall, it goes to
// sysenter(), which saves the register state (including RIP of SYSCALL
// instruction) to vCPU.registers.
// 2. It then calls KernelSyscall, which rewinds the IP and executes
// HLT.
// 3. HLT does a VM-exit to bluepillHandler, which returns from the
// signal handler using vCPU.registers, directly to the SYSCALL
// instruction.
// 4. Later, when we want to re-use the vCPU (perhaps on a different
// host thread), we set the new thread's registers in vCPU.registers
// (as opposed to setting the KVM registers with KVM_SET_REGS).
// 5. KVM_RUN thus enters the guest with the old register state,
// immediately following the HLT instruction, returning here.
// 6. We then restore FS_BASE and the full registers from vCPU.register
// to return from sysenter() back to the desired bluepill point from
// the host.
ring0.HaltAndWriteFSBase(regs) // escapes: no, reload host segment.
}
// KernelException handles kernel exceptions.
//
// +checkescape:all
//
//go:nosplit
func (c *vCPU) KernelException(vector ring0.Vector) {
regs := c.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 and a full stack trace.
regs.Rip = 0
}
// See above.
ring0.HaltAndWriteFSBase(regs) // escapes: no, reload host segment.
}
// 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
// Set the context pointer to the saved floating point state. This is
// where the guest data has been serialized, the kernel will restore
// from this new pointer value.
context.Fpstate = uint64(uintptrValue(c.FloatingPointState().BytePointer())) // escapes: no.
}
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