Add initial ptrace stub and syscall support for arm64.

Signed-off-by: Haibo Xu <haibo.xu@arm.com>
Change-Id: I1dbd23bb240cca71d0cc30fc75ca5be28cb4c37c
PiperOrigin-RevId: 262619519

pkg/abi/linux/elf.go

@@ -89,3 +89,17 @@ const (
 	// AT_SYSINFO_EHDR is the address of the VDSO.
 	AT_SYSINFO_EHDR = 33
 )
+
+// ELF ET_CORE and ptrace GETREGSET/SETREGSET register set types.
+//
+// See include/uapi/linux/elf.h.
+const (
+	// NT_PRSTATUS is for general purpose register.
+	NT_PRSTATUS = 0x1
+
+	// NT_PRFPREG is for float point register.
+	NT_PRFPREG = 0x2
+
+	// NT_X86_XSTATE is for x86 extended state using xsave.
+	NT_X86_XSTATE = 0x202
+)

pkg/sentry/platform/ptrace/BUILD

@@ -7,13 +7,17 @@ go_library(
     srcs = [
         "filters.go",
         "ptrace.go",
+        "ptrace_amd64.go",
+        "ptrace_arm64.go",
         "ptrace_unsafe.go",
         "stub_amd64.s",
+        "stub_arm64.s",
         "stub_unsafe.go",
         "subprocess.go",
         "subprocess_amd64.go",
+        "subprocess_arm64.go",
         "subprocess_linux.go",
-        "subprocess_linux_amd64_unsafe.go",
+        "subprocess_linux_unsafe.go",
         "subprocess_unsafe.go",
     ],
     importpath = "gvisor.dev/gvisor/pkg/sentry/platform/ptrace",

pkg/sentry/platform/ptrace/ptrace.go

@@ -60,7 +60,7 @@ var (
 	// maximum user address. This is valid only after a call to stubInit.
 	//
 	// We attempt to link the stub here, and adjust downward as needed.
-	stubStart uintptr = 0x7fffffff0000
+	stubStart uintptr = stubInitAddress
 
 	// stubEnd is the first byte past the end of the stub, as with
 	// stubStart this is valid only after a call to stubInit.

pkg/sentry/platform/ptrace/ptrace_amd64.go

@@ -0,0 +1,33 @@
+// Copyright 2019 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.
+
+package ptrace
+
+import (
+	"syscall"
+
+	"gvisor.dev/gvisor/pkg/abi/linux"
+)
+
+// fpRegSet returns the GETREGSET/SETREGSET register set type to be used.
+func fpRegSet(useXsave bool) uintptr {
+	if useXsave {
+		return linux.NT_X86_XSTATE
+	}
+	return linux.NT_PRFPREG
+}
+
+func stackPointer(r *syscall.PtraceRegs) uintptr {
+	return uintptr(r.Rsp)
+}

pkg/sentry/platform/ptrace/ptrace_arm64.go

@@ -0,0 +1,30 @@
+// Copyright 2019 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.
+
+package ptrace
+
+import (
+	"syscall"
+
+	"gvisor.dev/gvisor/pkg/abi/linux"
+)
+
+// fpRegSet returns the GETREGSET/SETREGSET register set type to be used.
+func fpRegSet(_ bool) uintptr {
+	return linux.NT_PRFPREG
+}
+
+func stackPointer(r *syscall.PtraceRegs) uintptr {
+	return uintptr(r.Sp)
+}

pkg/sentry/platform/ptrace/ptrace_unsafe.go

@@ -18,37 +18,23 @@ import (
 	"syscall"
 	"unsafe"
 
+	"gvisor.dev/gvisor/pkg/abi/linux"
 	"gvisor.dev/gvisor/pkg/sentry/arch"
 	"gvisor.dev/gvisor/pkg/sentry/usermem"
 )
 
-// GETREGSET/SETREGSET register set types.
-//
-// See include/uapi/linux/elf.h.
-const (
-	// _NT_PRFPREG is for x86 floating-point state without using xsave.
-	_NT_PRFPREG = 0x2
-
-	// _NT_X86_XSTATE is for x86 extended state using xsave.
-	_NT_X86_XSTATE = 0x202
-)
-
-// fpRegSet returns the GETREGSET/SETREGSET register set type to be used.
-func fpRegSet(useXsave bool) uintptr {
-	if useXsave {
-		return _NT_X86_XSTATE
-	}
-	return _NT_PRFPREG
-}
-
-// getRegs sets the regular register set.
+// getRegs gets the general purpose register set.
 func (t *thread) getRegs(regs *syscall.PtraceRegs) error {
+	iovec := syscall.Iovec{
+		Base: (*byte)(unsafe.Pointer(regs)),
+		Len:  uint64(unsafe.Sizeof(*regs)),
+	}
 	_, _, errno := syscall.RawSyscall6(
 		syscall.SYS_PTRACE,
-		syscall.PTRACE_GETREGS,
+		syscall.PTRACE_GETREGSET,
 		uintptr(t.tid),
-		0,
-		uintptr(unsafe.Pointer(regs)),
+		linux.NT_PRSTATUS,
+		uintptr(unsafe.Pointer(&iovec)),
 		0, 0)
 	if errno != 0 {
 		return errno
@@ -56,14 +42,18 @@ func (t *thread) getRegs(regs *syscall.PtraceRegs) error {
 	return nil
 }
 
-// setRegs sets the regular register set.
+// setRegs sets the general purpose register set.
 func (t *thread) setRegs(regs *syscall.PtraceRegs) error {
+	iovec := syscall.Iovec{
+		Base: (*byte)(unsafe.Pointer(regs)),
+		Len:  uint64(unsafe.Sizeof(*regs)),
+	}
 	_, _, errno := syscall.RawSyscall6(
 		syscall.SYS_PTRACE,
-		syscall.PTRACE_SETREGS,
+		syscall.PTRACE_SETREGSET,
 		uintptr(t.tid),
-		0,
-		uintptr(unsafe.Pointer(regs)),
+		linux.NT_PRSTATUS,
+		uintptr(unsafe.Pointer(&iovec)),
 		0, 0)
 	if errno != 0 {
 		return errno
@@ -131,7 +121,7 @@ func (t *thread) getSignalInfo(si *arch.SignalInfo) error {
 //
 // Precondition: the OS thread must be locked and own t.
 func (t *thread) clone() (*thread, error) {
-	r, ok := usermem.Addr(t.initRegs.Rsp).RoundUp()
+	r, ok := usermem.Addr(stackPointer(&t.initRegs)).RoundUp()
 	if !ok {
 		return nil, syscall.EINVAL
 	}

pkg/sentry/platform/ptrace/stub_arm64.s

@@ -0,0 +1,106 @@
+// Copyright 2019 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"
+
+#define SYS_GETPID		172
+#define SYS_EXIT		93
+#define SYS_KILL		129
+#define SYS_GETPPID		173
+#define SYS_PRCTL		167
+
+#define SIGKILL			9
+#define SIGSTOP			19
+
+#define PR_SET_PDEATHSIG	1
+
+// stub bootstraps the child and sends itself SIGSTOP to wait for attach.
+//
+// R7 contains the expected PPID.
+//
+// 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.
+
+	MOVD $SYS_PRCTL, R8
+	MOVD $PR_SET_PDEATHSIG, R0
+	MOVD $SIGKILL, R1
+	SVC
+
+	CMN $4095, R0
+	BCS error
+
+	// If the parent already died before we called PR_SET_DEATHSIG then
+	// we'll have an unexpected PPID.
+	MOVD $SYS_GETPPID, R8
+	SVC
+
+	CMP R0, R7
+	BNE parent_dead
+
+	MOVD $SYS_GETPID, R8
+	SVC
+
+	CMP $0x0, R0
+	BLT error
+
+	// SIGSTOP to wait for attach.
+	//
+	// The SYSCALL instruction will be used for future syscall injection by
+	// thread.syscall.
+	MOVD $SYS_KILL, R8
+	MOVD $SIGSTOP, R1
+	SVC
+	// 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.
+	//
+	// R7 has been updated with the expected PPID.
+	B begin
+
+error:
+	// Exit with -errno.
+	NEG R0, R0
+	MOVD $SYS_EXIT, R8
+	SVC
+	HLT
+
+parent_dead:
+	MOVD $SYS_EXIT, R8
+	MOVD $1, R0
+	SVC
+	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
+	MOVD addr+0(FP), R0
+	MOVD pid+8(FP), R7
+	B (R0)

pkg/sentry/platform/ptrace/subprocess.go

@@ -28,6 +28,16 @@ import (
 	"gvisor.dev/gvisor/pkg/sentry/usermem"
 )
 
+// Linux kernel errnos which "should never be seen by user programs", but will
+// be revealed to ptrace syscall exit tracing.
+//
+// These constants are only used in subprocess.go.
+const (
+	ERESTARTSYS    = syscall.Errno(512)
+	ERESTARTNOINTR = syscall.Errno(513)
+	ERESTARTNOHAND = syscall.Errno(514)
+)
+
 // globalPool exists to solve two distinct problems:
 //
 // 1) Subprocesses can't always be killed properly (see Release).
@@ -282,7 +292,7 @@ func (t *thread) grabInitRegs() {
 	if err := t.getRegs(&t.initRegs); err != nil {
 		panic(fmt.Sprintf("ptrace get regs failed: %v", err))
 	}
-	t.initRegs.Rip -= initRegsRipAdjustment
+	t.adjustInitRegsRip()
 }
 
 // detach detaches from the thread.

pkg/sentry/platform/ptrace/subprocess_amd64.go

@@ -28,20 +28,13 @@ const (
 	// maximumUserAddress is the largest possible user address.
 	maximumUserAddress = 0x7ffffffff000
 
+	// stubInitAddress is the initial attempt link address for the stub.
+	stubInitAddress = 0x7fffffff0000
+
 	// initRegsRipAdjustment is the size of the syscall instruction.
 	initRegsRipAdjustment = 2
 )
 
-// Linux kernel errnos which "should never be seen by user programs", but will
-// be revealed to ptrace syscall exit tracing.
-//
-// These constants are used in subprocess.go.
-const (
-	ERESTARTSYS    = syscall.Errno(512)
-	ERESTARTNOINTR = syscall.Errno(513)
-	ERESTARTNOHAND = syscall.Errno(514)
-)
-
 // resetSysemuRegs sets up emulation registers.
 //
 // This should be called prior to calling sysemu.
@@ -139,3 +132,14 @@ func dumpRegs(regs *syscall.PtraceRegs) string {
 
 	return m.String()
 }
+
+// adjustInitregsRip adjust the current register RIP value to
+// be just before the system call instruction excution
+func (t *thread) adjustInitRegsRip() {
+	t.initRegs.Rip -= initRegsRipAdjustment
+}
+
+// Pass the expected PPID to the child via R15 when creating stub process
+func initChildProcessPPID(initregs *syscall.PtraceRegs, ppid int32) {
+	initregs.R15 = uint64(ppid)
+}

pkg/sentry/platform/ptrace/subprocess_arm64.go

@@ -0,0 +1,126 @@
+// Copyright 2019 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.
+
+// +build arm64
+
+package ptrace
+
+import (
+	"syscall"
+
+	"gvisor.dev/gvisor/pkg/sentry/arch"
+)
+
+const (
+	// maximumUserAddress is the largest possible user address.
+	maximumUserAddress = 0xfffffffff000
+
+	// stubInitAddress is the initial attempt link address for the stub.
+	// Only support 48bits VA currently.
+	stubInitAddress = 0xffffffff0000
+
+	// initRegsRipAdjustment is the size of the svc instruction.
+	initRegsRipAdjustment = 4
+)
+
+// resetSysemuRegs sets up emulation registers.
+//
+// This should be called prior to calling sysemu.
+func (s *subprocess) resetSysemuRegs(regs *syscall.PtraceRegs) {
+}
+
+// createSyscallRegs sets up syscall registers.
+//
+// This should be called to generate registers for a system call.
+func createSyscallRegs(initRegs *syscall.PtraceRegs, sysno uintptr, args ...arch.SyscallArgument) syscall.PtraceRegs {
+	// Copy initial registers (Pc, Sp, etc.).
+	regs := *initRegs
+
+	// Set our syscall number.
+	// r8 for the syscall number.
+	// r0-r6 is used to store the parameters.
+	regs.Regs[8] = uint64(sysno)
+	if len(args) >= 1 {
+		regs.Regs[0] = args[0].Uint64()
+	}
+	if len(args) >= 2 {
+		regs.Regs[1] = args[1].Uint64()
+	}
+	if len(args) >= 3 {
+		regs.Regs[2] = args[2].Uint64()
+	}
+	if len(args) >= 4 {
+		regs.Regs[3] = args[3].Uint64()
+	}
+	if len(args) >= 5 {
+		regs.Regs[4] = args[4].Uint64()
+	}
+	if len(args) >= 6 {
+		regs.Regs[5] = args[5].Uint64()
+	}
+
+	return regs
+}
+
+// isSingleStepping determines if the registers indicate single-stepping.
+func isSingleStepping(regs *syscall.PtraceRegs) bool {
+	// Refer to the ARM SDM D2.12.3: software step state machine
+	// return (regs.Pstate.SS == 1) && (MDSCR_EL1.SS == 1).
+	//
+	// Since the host Linux kernel will set MDSCR_EL1.SS on our behalf
+	// when we call a single-step ptrace command, we only need to check
+	// the Pstate.SS bit here.
+	return (regs.Pstate & arch.ARMTrapFlag) != 0
+}
+
+// updateSyscallRegs updates registers after finishing sysemu.
+func updateSyscallRegs(regs *syscall.PtraceRegs) {
+	// No special work is necessary.
+	return
+}
+
+// syscallReturnValue extracts a sensible return from registers.
+func syscallReturnValue(regs *syscall.PtraceRegs) (uintptr, error) {
+	rval := int64(regs.Regs[0])
+	if rval < 0 {
+		return 0, syscall.Errno(-rval)
+	}
+	return uintptr(rval), nil
+}
+
+func dumpRegs(regs *syscall.PtraceRegs) string {
+	var m strings.Builder
+
+	fmt.Fprintf(&m, "Registers:\n")
+
+	for i := 0; i < 31; i++ {
+		fmt.Fprintf(&m, "\tRegs[%d]\t = %016x\n", i, regs.Regs[i])
+	}
+	fmt.Fprintf(&m, "\tSp\t = %016x\n", regs.Sp)
+	fmt.Fprintf(&m, "\tPc\t = %016x\n", regs.Pc)
+	fmt.Fprintf(&m, "\tPstate\t = %016x\n", regs.Pstate)
+
+	return m.String()
+}
+
+// adjustInitregsRip adjust the current register RIP value to
+// be just before the system call instruction excution
+func (t *thread) adjustInitRegsRip() {
+	t.initRegs.Pc -= initRegsRipAdjustment
+}
+
+// Pass the expected PPID to the child via X7 when creating stub process
+func initChildProcessPPID(initregs *syscall.PtraceRegs, ppid int32) {
+	initregs.Regs[7] = uint64(ppid)
+}

pkg/sentry/platform/ptrace/subprocess_linux.go

@@ -284,7 +284,7 @@ func (s *subprocess) createStub() (*thread, error) {
 
 	// Pass the expected PPID to the child via R15.
 	regs := t.initRegs
-	regs.R15 = uint64(t.tgid)
+	initChildProcessPPID(&regs, t.tgid)
 
 	// Call fork in a subprocess.
 	//

pkg/sentry/platform/ptrace/subprocess_linux_unsafe.go

@@ -12,7 +12,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-// +build amd64 linux
+// +build linux
+// +build amd64 arm64
 
 package ptrace