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// Copyright 2018 Google LLC
//
// 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 "textflag.h"
// VCPU_CPU is the location of the CPU in the vCPU struct.
//
// This is guaranteed to be zero.
#define VCPU_CPU 0x0
// CPU_SELF is the self reference in ring0's percpu.
//
// This is guaranteed to be zero.
#define CPU_SELF 0x0
// Context offsets.
//
// Only limited use of the context is done in the assembly stub below, most is
// done in the Go handlers. However, the RIP must be examined.
#define CONTEXT_RAX 0x90
#define CONTEXT_RIP 0xa8
#define CONTEXT_FP 0xe0
// CLI is the literal byte for the disable interrupts instruction.
//
// This is checked as the source of the fault.
#define CLI $0xfa
// See bluepill.go.
TEXT ·bluepill(SB),NOSPLIT,$0
begin:
MOVQ vcpu+0(FP), AX
LEAQ VCPU_CPU(AX), BX
BYTE CLI;
check_vcpu:
MOVQ CPU_SELF(GS), CX
CMPQ BX, CX
JE right_vCPU
wrong_vcpu:
CALL ·redpill(SB)
JMP begin
right_vCPU:
RET
// sighandler: see bluepill.go for documentation.
//
// The arguments are the following:
//
// DI - The signal number.
// SI - Pointer to siginfo_t structure.
// DX - Pointer to ucontext structure.
//
TEXT ·sighandler(SB),NOSPLIT,$0
// Check if the signal is from the kernel.
MOVQ $0x80, CX
CMPL CX, 0x8(SI)
JNE fallback
// Check if RIP is disable interrupts.
MOVQ CONTEXT_RIP(DX), CX
CMPQ CX, $0x0
JE fallback
CMPB 0(CX), CLI
JNE fallback
// Call the bluepillHandler.
PUSHQ DX // First argument (context).
CALL ·bluepillHandler(SB) // Call the handler.
POPQ DX // Discard the argument.
RET
fallback:
// Jump to the previous signal handler.
XORQ CX, CX
MOVQ ·savedHandler(SB), AX
JMP AX
// dieTrampoline: see bluepill.go, bluepill_amd64_unsafe.go for documentation.
TEXT ·dieTrampoline(SB),NOSPLIT,$0
PUSHQ BX // First argument (vCPU).
PUSHQ AX // Fake the old RIP as caller.
JMP ·dieHandler(SB)
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