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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 "funcdata.h"
#include "textflag.h"
#define SYS_GETPID 39
#define SYS_EXIT 60
#define SYS_KILL 62
#define SYS_GETPPID 110
#define SYS_PRCTL 157
#define SIGKILL 9
#define SIGSTOP 19
#define PR_SET_PDEATHSIG 1
// stub bootstraps the child and sends itself SIGSTOP to wait for attach.
//
// R15 contains the expected PPID. R15 is used instead of a more typical DI
// since syscalls will clobber DI and createStub wants to pass a new PPID to
// grandchildren.
//
// This should not be used outside the context of a new ptrace child (as the
// function is otherwise a bunch of nonsense).
TEXT ·stub(SB),NOSPLIT,$0
begin:
// N.B. This loop only executes in the context of a single-threaded
// fork child.
MOVQ $SYS_PRCTL, AX
MOVQ $PR_SET_PDEATHSIG, DI
MOVQ $SIGKILL, SI
SYSCALL
CMPQ AX, $0
JNE error
// If the parent already died before we called PR_SET_DEATHSIG then
// we'll have an unexpected PPID.
MOVQ $SYS_GETPPID, AX
SYSCALL
CMPQ AX, $0
JL error
CMPQ AX, R15
JNE parent_dead
MOVQ $SYS_GETPID, AX
SYSCALL
CMPQ AX, $0
JL error
// SIGSTOP to wait for attach.
//
// The SYSCALL instruction will be used for future syscall injection by
// thread.syscall.
MOVQ AX, DI
MOVQ $SYS_KILL, AX
MOVQ $SIGSTOP, SI
SYSCALL
// The tracer may "detach" and/or allow code execution here in three cases:
//
// 1. New (traced) stub threads are explicitly detached by the
// goroutine in newSubprocess. However, they are detached while in
// group-stop, so they do not execute code here.
//
// 2. If a tracer thread exits, it implicitly detaches from the stub,
// potentially allowing code execution here. However, the Go runtime
// never exits individual threads, so this case never occurs.
//
// 3. subprocess.createStub clones a new stub process that is untraced,
// thus executing this code. We setup the PDEATHSIG before SIGSTOPing
// ourselves for attach by the tracer.
//
// R15 has been updated with the expected PPID.
JMP begin
error:
// Exit with -errno.
MOVQ AX, DI
NEGQ DI
MOVQ $SYS_EXIT, AX
SYSCALL
HLT
parent_dead:
MOVQ $SYS_EXIT, AX
MOVQ $1, DI
SYSCALL
HLT
// stubCall calls the stub function at the given address with the given PPID.
//
// This is a distinct function because stub, above, may be mapped at any
// arbitrary location, and stub has a specific binary API (see above).
TEXT ·stubCall(SB),NOSPLIT,$0-16
MOVQ addr+0(FP), AX
MOVQ pid+8(FP), R15
JMP AX
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