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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.
#include "funcdata.h"
#include "textflag.h"
// NB: Offsets are programmatically generated (see BUILD).
//
// This file is concatenated with the definitions.
// Saves a register set.
//
// This is a macro because it may need to executed in contents where a stack is
// not available for calls.
//
// The following registers are not saved: AX, SP, IP, FLAGS, all segments.
#define REGISTERS_SAVE(reg, offset) \
MOVQ R15, offset+PTRACE_R15(reg); \
MOVQ R14, offset+PTRACE_R14(reg); \
MOVQ R13, offset+PTRACE_R13(reg); \
MOVQ R12, offset+PTRACE_R12(reg); \
MOVQ BP, offset+PTRACE_RBP(reg); \
MOVQ BX, offset+PTRACE_RBX(reg); \
MOVQ CX, offset+PTRACE_RCX(reg); \
MOVQ DX, offset+PTRACE_RDX(reg); \
MOVQ R11, offset+PTRACE_R11(reg); \
MOVQ R10, offset+PTRACE_R10(reg); \
MOVQ R9, offset+PTRACE_R9(reg); \
MOVQ R8, offset+PTRACE_R8(reg); \
MOVQ SI, offset+PTRACE_RSI(reg); \
MOVQ DI, offset+PTRACE_RDI(reg);
// Loads a register set.
//
// This is a macro because it may need to executed in contents where a stack is
// not available for calls.
//
// The following registers are not loaded: AX, SP, IP, FLAGS, all segments.
#define REGISTERS_LOAD(reg, offset) \
MOVQ offset+PTRACE_R15(reg), R15; \
MOVQ offset+PTRACE_R14(reg), R14; \
MOVQ offset+PTRACE_R13(reg), R13; \
MOVQ offset+PTRACE_R12(reg), R12; \
MOVQ offset+PTRACE_RBP(reg), BP; \
MOVQ offset+PTRACE_RBX(reg), BX; \
MOVQ offset+PTRACE_RCX(reg), CX; \
MOVQ offset+PTRACE_RDX(reg), DX; \
MOVQ offset+PTRACE_R11(reg), R11; \
MOVQ offset+PTRACE_R10(reg), R10; \
MOVQ offset+PTRACE_R9(reg), R9; \
MOVQ offset+PTRACE_R8(reg), R8; \
MOVQ offset+PTRACE_RSI(reg), SI; \
MOVQ offset+PTRACE_RDI(reg), DI;
// WRITE_CR3() writes the given CR3 value.
//
// The code corresponds to:
//
// mov %rax, %cr3
//
#define WRITE_CR3() \
BYTE $0x0f; BYTE $0x22; BYTE $0xd8;
// SWAP_GS swaps the kernel GS (CPU).
#define SWAP_GS() \
BYTE $0x0F; BYTE $0x01; BYTE $0xf8;
// IRET returns from an interrupt frame.
#define IRET() \
BYTE $0x48; BYTE $0xcf;
// SYSRET64 executes the sysret instruction.
#define SYSRET64() \
BYTE $0x48; BYTE $0x0f; BYTE $0x07;
// LOAD_KERNEL_STACK loads the kernel stack.
#define LOAD_KERNEL_STACK(entry) \
MOVQ ENTRY_STACK_TOP(entry), SP;
// See kernel.go.
TEXT ·Halt(SB),NOSPLIT,$0
HLT
RET
// See entry_amd64.go.
TEXT ·swapgs(SB),NOSPLIT,$0
SWAP_GS()
RET
// jumpToKernel changes execution to the kernel address space.
//
// This works by changing the return value to the kernel version.
TEXT ·jumpToKernel(SB),NOSPLIT,$0
MOVQ 0(SP), AX
ORQ ·KernelStartAddress(SB), AX // Future return value.
MOVQ AX, 0(SP)
RET
// See entry_amd64.go.
TEXT ·sysret(SB),NOSPLIT,$0-24
CALL ·jumpToKernel(SB)
// Save original state and stack. sysenter() or exception()
// from APP(gr3) will switch to this stack, set the return
// value (vector: 32(SP)) and then do RET, which will also
// automatically return to the lower half.
MOVQ cpu+0(FP), BX
MOVQ regs+8(FP), AX
MOVQ userCR3+16(FP), CX
MOVQ SP, CPU_REGISTERS+PTRACE_RSP(BX)
MOVQ BP, CPU_REGISTERS+PTRACE_RBP(BX)
MOVQ AX, CPU_REGISTERS+PTRACE_RAX(BX)
// save SP AX userCR3 on the kernel stack.
MOVQ CPU_ENTRY(BX), BX
LOAD_KERNEL_STACK(BX)
PUSHQ PTRACE_RSP(AX)
PUSHQ PTRACE_RAX(AX)
PUSHQ CX
// Restore user register state.
REGISTERS_LOAD(AX, 0)
MOVQ PTRACE_RIP(AX), CX // Needed for SYSRET.
MOVQ PTRACE_FLAGS(AX), R11 // Needed for SYSRET.
// restore userCR3, AX, SP.
POPQ AX // Get userCR3.
WRITE_CR3() // Switch to userCR3.
POPQ AX // Restore AX.
POPQ SP // Restore SP.
SYSRET64()
// See entry_amd64.go.
TEXT ·iret(SB),NOSPLIT,$0-24
CALL ·jumpToKernel(SB)
// Save original state and stack. sysenter() or exception()
// from APP(gr3) will switch to this stack, set the return
// value (vector: 32(SP)) and then do RET, which will also
// automatically return to the lower half.
MOVQ cpu+0(FP), BX
MOVQ regs+8(FP), AX
MOVQ userCR3+16(FP), CX
MOVQ SP, CPU_REGISTERS+PTRACE_RSP(BX)
MOVQ BP, CPU_REGISTERS+PTRACE_RBP(BX)
MOVQ AX, CPU_REGISTERS+PTRACE_RAX(BX)
// Build an IRET frame & restore state.
MOVQ CPU_ENTRY(BX), BX
LOAD_KERNEL_STACK(BX)
PUSHQ PTRACE_SS(AX)
PUSHQ PTRACE_RSP(AX)
PUSHQ PTRACE_FLAGS(AX)
PUSHQ PTRACE_CS(AX)
PUSHQ PTRACE_RIP(AX)
PUSHQ PTRACE_RAX(AX) // Save AX on kernel stack.
PUSHQ CX // Save userCR3 on kernel stack.
REGISTERS_LOAD(AX, 0) // Restore most registers.
POPQ AX // Get userCR3.
WRITE_CR3() // Switch to userCR3.
POPQ AX // Restore AX.
IRET()
// See entry_amd64.go.
TEXT ·resume(SB),NOSPLIT,$0
// See iret, above.
MOVQ ENTRY_CPU_SELF(GS), AX // Load vCPU.
PUSHQ CPU_REGISTERS+PTRACE_SS(AX)
PUSHQ CPU_REGISTERS+PTRACE_RSP(AX)
PUSHQ CPU_REGISTERS+PTRACE_FLAGS(AX)
PUSHQ CPU_REGISTERS+PTRACE_CS(AX)
PUSHQ CPU_REGISTERS+PTRACE_RIP(AX)
REGISTERS_LOAD(AX, CPU_REGISTERS)
MOVQ CPU_REGISTERS+PTRACE_RAX(AX), AX
IRET()
// See entry_amd64.go.
TEXT ·Start(SB),NOSPLIT,$0
PUSHQ $0x0 // Previous frame pointer.
MOVQ SP, BP // Set frame pointer.
PUSHQ AX // First argument (CPU).
CALL ·start(SB) // Call Go hook.
JMP ·resume(SB) // Restore to registers.
// See entry_amd64.go.
TEXT ·sysenter(SB),NOSPLIT,$0
// _RFLAGS_IOPL0 is always set in the user mode and it is never set in
// the kernel mode. See the comment of UserFlagsSet for more details.
TESTL $_RFLAGS_IOPL0, R11
JZ kernel
user:
SWAP_GS()
MOVQ AX, ENTRY_SCRATCH0(GS) // Save user AX on scratch.
MOVQ ENTRY_KERNEL_CR3(GS), AX // Get kernel cr3 on AX.
WRITE_CR3() // Switch to kernel cr3.
MOVQ ENTRY_CPU_SELF(GS), AX // Load vCPU.
MOVQ CPU_REGISTERS+PTRACE_RAX(AX), AX // Get user regs.
REGISTERS_SAVE(AX, 0) // Save all except IP, FLAGS, SP, AX.
MOVQ CX, PTRACE_RIP(AX)
MOVQ R11, PTRACE_FLAGS(AX)
MOVQ SP, PTRACE_RSP(AX)
MOVQ ENTRY_SCRATCH0(GS), CX // Load saved user AX value.
MOVQ CX, PTRACE_RAX(AX) // Save everything else.
MOVQ CX, PTRACE_ORIGRAX(AX)
MOVQ ENTRY_CPU_SELF(GS), AX // Load vCPU.
MOVQ CPU_REGISTERS+PTRACE_RSP(AX), SP // Get stacks.
MOVQ $0, CPU_ERROR_CODE(AX) // Clear error code.
MOVQ $1, CPU_ERROR_TYPE(AX) // Set error type to user.
// Return to the kernel, where the frame is:
//
// vector (sp+32)
// userCR3 (sp+24)
// regs (sp+16)
// cpu (sp+8)
// vcpu.Switch (sp+0)
//
MOVQ CPU_REGISTERS+PTRACE_RBP(AX), BP // Original base pointer.
MOVQ $Syscall, 32(SP) // Output vector.
RET
kernel:
// We can't restore the original stack, but we can access the registers
// in the CPU state directly. No need for temporary juggling.
MOVQ AX, ENTRY_SCRATCH0(GS)
MOVQ ENTRY_CPU_SELF(GS), AX // Load vCPU.
REGISTERS_SAVE(AX, CPU_REGISTERS)
MOVQ CX, CPU_REGISTERS+PTRACE_RIP(AX)
MOVQ R11, CPU_REGISTERS+PTRACE_FLAGS(AX)
MOVQ SP, CPU_REGISTERS+PTRACE_RSP(AX)
MOVQ ENTRY_SCRATCH0(GS), BX
MOVQ BX, CPU_REGISTERS+PTRACE_ORIGRAX(AX)
MOVQ BX, CPU_REGISTERS+PTRACE_RAX(AX)
MOVQ $0, CPU_ERROR_CODE(AX) // Clear error code.
MOVQ $0, CPU_ERROR_TYPE(AX) // Set error type to kernel.
// Call the syscall trampoline.
LOAD_KERNEL_STACK(GS)
PUSHQ AX // First argument (vCPU).
CALL ·kernelSyscall(SB) // Call the trampoline.
POPQ AX // Pop vCPU.
JMP ·resume(SB)
// exception is a generic exception handler.
//
// There are two cases handled:
//
// 1) An exception in kernel mode: this results in saving the state at the time
// of the exception and calling the defined hook.
//
// 2) An exception in guest mode: the original kernel frame is restored, and
// the vector & error codes are pushed as return values.
//
// See below for the stubs that call exception.
TEXT ·exception(SB),NOSPLIT,$0
// Determine whether the exception occurred in kernel mode or user
// mode, based on the flags. We expect the following stack:
//
// SS (sp+48)
// SP (sp+40)
// FLAGS (sp+32)
// CS (sp+24)
// IP (sp+16)
// ERROR_CODE (sp+8)
// VECTOR (sp+0)
//
TESTL $_RFLAGS_IOPL0, 32(SP)
JZ kernel
user:
SWAP_GS()
ADDQ $-8, SP // Adjust for flags.
MOVQ $_KERNEL_FLAGS, 0(SP); BYTE $0x9d; // Reset flags (POPFQ).
PUSHQ AX // Save user AX on stack.
MOVQ ENTRY_KERNEL_CR3(GS), AX // Get kernel cr3 on AX.
WRITE_CR3() // Switch to kernel cr3.
MOVQ ENTRY_CPU_SELF(GS), AX // Load vCPU.
MOVQ CPU_REGISTERS+PTRACE_RAX(AX), AX // Get user regs.
REGISTERS_SAVE(AX, 0) // Save all except IP, FLAGS, SP, AX.
POPQ BX // Restore original AX.
MOVQ BX, PTRACE_RAX(AX) // Save it.
MOVQ BX, PTRACE_ORIGRAX(AX)
MOVQ 16(SP), BX; MOVQ BX, PTRACE_RIP(AX)
MOVQ 24(SP), CX; MOVQ CX, PTRACE_CS(AX)
MOVQ 32(SP), DX; MOVQ DX, PTRACE_FLAGS(AX)
MOVQ 40(SP), DI; MOVQ DI, PTRACE_RSP(AX)
MOVQ 48(SP), SI; MOVQ SI, PTRACE_SS(AX)
// Copy out and return.
MOVQ ENTRY_CPU_SELF(GS), AX // Load vCPU.
MOVQ 0(SP), BX // Load vector.
MOVQ 8(SP), CX // Load error code.
MOVQ CPU_REGISTERS+PTRACE_RSP(AX), SP // Original stack (kernel version).
MOVQ CPU_REGISTERS+PTRACE_RBP(AX), BP // Original base pointer.
MOVQ CX, CPU_ERROR_CODE(AX) // Set error code.
MOVQ $1, CPU_ERROR_TYPE(AX) // Set error type to user.
MOVQ BX, 32(SP) // Output vector.
RET
kernel:
// As per above, we can save directly.
PUSHQ AX
MOVQ ENTRY_CPU_SELF(GS), AX // Load vCPU.
REGISTERS_SAVE(AX, CPU_REGISTERS)
POPQ BX
MOVQ BX, CPU_REGISTERS+PTRACE_RAX(AX)
MOVQ BX, CPU_REGISTERS+PTRACE_ORIGRAX(AX)
MOVQ 16(SP), BX; MOVQ BX, CPU_REGISTERS+PTRACE_RIP(AX)
MOVQ 32(SP), BX; MOVQ BX, CPU_REGISTERS+PTRACE_FLAGS(AX)
MOVQ 40(SP), BX; MOVQ BX, CPU_REGISTERS+PTRACE_RSP(AX)
// Set the error code and adjust the stack.
MOVQ 8(SP), BX // Load the error code.
MOVQ BX, CPU_ERROR_CODE(AX) // Copy out to the CPU.
MOVQ $0, CPU_ERROR_TYPE(AX) // Set error type to kernel.
MOVQ 0(SP), BX // BX contains the vector.
// Call the exception trampoline.
LOAD_KERNEL_STACK(GS)
PUSHQ BX // Second argument (vector).
PUSHQ AX // First argument (vCPU).
CALL ·kernelException(SB) // Call the trampoline.
POPQ BX // Pop vector.
POPQ AX // Pop vCPU.
JMP ·resume(SB)
#define EXCEPTION_WITH_ERROR(value, symbol) \
TEXT symbol,NOSPLIT,$0; \
PUSHQ $value; \
JMP ·exception(SB);
#define EXCEPTION_WITHOUT_ERROR(value, symbol) \
TEXT symbol,NOSPLIT,$0; \
PUSHQ $0x0; \
PUSHQ $value; \
JMP ·exception(SB);
EXCEPTION_WITHOUT_ERROR(DivideByZero, ·divideByZero(SB))
EXCEPTION_WITHOUT_ERROR(Debug, ·debug(SB))
EXCEPTION_WITHOUT_ERROR(NMI, ·nmi(SB))
EXCEPTION_WITHOUT_ERROR(Breakpoint, ·breakpoint(SB))
EXCEPTION_WITHOUT_ERROR(Overflow, ·overflow(SB))
EXCEPTION_WITHOUT_ERROR(BoundRangeExceeded, ·boundRangeExceeded(SB))
EXCEPTION_WITHOUT_ERROR(InvalidOpcode, ·invalidOpcode(SB))
EXCEPTION_WITHOUT_ERROR(DeviceNotAvailable, ·deviceNotAvailable(SB))
EXCEPTION_WITH_ERROR(DoubleFault, ·doubleFault(SB))
EXCEPTION_WITHOUT_ERROR(CoprocessorSegmentOverrun, ·coprocessorSegmentOverrun(SB))
EXCEPTION_WITH_ERROR(InvalidTSS, ·invalidTSS(SB))
EXCEPTION_WITH_ERROR(SegmentNotPresent, ·segmentNotPresent(SB))
EXCEPTION_WITH_ERROR(StackSegmentFault, ·stackSegmentFault(SB))
EXCEPTION_WITH_ERROR(GeneralProtectionFault, ·generalProtectionFault(SB))
EXCEPTION_WITH_ERROR(PageFault, ·pageFault(SB))
EXCEPTION_WITHOUT_ERROR(X87FloatingPointException, ·x87FloatingPointException(SB))
EXCEPTION_WITH_ERROR(AlignmentCheck, ·alignmentCheck(SB))
EXCEPTION_WITHOUT_ERROR(MachineCheck, ·machineCheck(SB))
EXCEPTION_WITHOUT_ERROR(SIMDFloatingPointException, ·simdFloatingPointException(SB))
EXCEPTION_WITHOUT_ERROR(VirtualizationException, ·virtualizationException(SB))
EXCEPTION_WITH_ERROR(SecurityException, ·securityException(SB))
EXCEPTION_WITHOUT_ERROR(SyscallInt80, ·syscallInt80(SB))
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