Enable thread local storage support on arm64.

Linux use the task.thread.uw.tp_value field to store the
TLS pointer on arm64 platform, and we use a similar way
in gvisor to store it in the arch/State struct.

Signed-off-by: Haibo Xu <haibo.xu@arm.com>
Change-Id: Ie76b5c6d109bc27ccfd594008a96753806db7764

pkg/abi/linux/elf.go

@@ -102,4 +102,7 @@ const (
 
 	// NT_X86_XSTATE is for x86 extended state using xsave.
 	NT_X86_XSTATE = 0x202
+
+	// NT_ARM_TLS is for ARM TLS register.
+	NT_ARM_TLS = 0x401
 )

pkg/sentry/arch/arch_aarch64.go

@@ -95,6 +95,9 @@ type State struct {
 	// Our floating point state.
 	aarch64FPState `state:"wait"`
 
+	// TLS pointer
+	TPValue uint64
+
 	// FeatureSet is a pointer to the currently active feature set.
 	FeatureSet *cpuid.FeatureSet
 }
@@ -145,6 +148,7 @@ func (s *State) Fork() State {
 	return State{
 		Regs:           s.Regs,
 		aarch64FPState: s.aarch64FPState.fork(),
+		TPValue:        s.TPValue,
 		FeatureSet:     s.FeatureSet,
 	}
 }
@@ -255,6 +259,7 @@ func (s *State) PtraceSetFPRegs(src io.Reader) (int, error) {
 const (
 	_NT_PRSTATUS = 1
 	_NT_PRFPREG  = 2
+	_NT_ARM_TLS  = 0x401
 )
 
 // PtraceGetRegSet implements Context.PtraceGetRegSet.

pkg/sentry/arch/arch_arm64.go

@@ -140,16 +140,17 @@ func (c *context64) SetStack(value uintptr) {
 
 // TLS returns the current TLS pointer.
 func (c *context64) TLS() uintptr {
-	// TODO(gvisor.dev/issue/1238): TLS is not supported.
-	// MRS_TPIDR_EL0
-	return 0
+	return uintptr(c.TPValue)
 }
 
 // SetTLS sets the current TLS pointer. Returns false if value is invalid.
 func (c *context64) SetTLS(value uintptr) bool {
-	// TODO(gvisor.dev/issue/1238): TLS is not supported.
-	// MSR_TPIDR_EL0
-	return false
+	if value >= uintptr(maxAddr64) {
+		return false
+	}
+
+	c.TPValue = uint64(value)
+	return true
 }
 
 // SetOldRSeqInterruptedIP implements Context.SetOldRSeqInterruptedIP.

pkg/sentry/platform/ptrace/BUILD

@@ -9,6 +9,7 @@ go_library(
         "ptrace.go",
         "ptrace_amd64.go",
         "ptrace_arm64.go",
+        "ptrace_arm64_unsafe.go",
         "ptrace_unsafe.go",
         "stub_amd64.s",
         "stub_arm64.s",

pkg/sentry/platform/ptrace/ptrace_amd64.go

@@ -31,3 +31,17 @@ func fpRegSet(useXsave bool) uintptr {
 func stackPointer(r *syscall.PtraceRegs) uintptr {
 	return uintptr(r.Rsp)
 }
+
+// x86 use the fs_base register to store the TLS pointer which can be
+// get/set in "func (t *thread) get/setRegs(regs *syscall.PtraceRegs)".
+// So both of the get/setTLS() operations are noop here.
+
+// getTLS gets the thread local storage register.
+func (t *thread) getTLS(tls *uint64) error {
+	return nil
+}
+
+// setTLS sets the thread local storage register.
+func (t *thread) setTLS(tls *uint64) error {
+	return nil
+}

pkg/sentry/platform/ptrace/ptrace_arm64_unsafe.go

@@ -0,0 +1,62 @@
+// Copyright 2020 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"
+	"unsafe"
+
+	"gvisor.dev/gvisor/pkg/abi/linux"
+)
+
+// getTLS gets the thread local storage register.
+func (t *thread) getTLS(tls *uint64) error {
+	iovec := syscall.Iovec{
+		Base: (*byte)(unsafe.Pointer(tls)),
+		Len:  uint64(unsafe.Sizeof(*tls)),
+	}
+	_, _, errno := syscall.RawSyscall6(
+		syscall.SYS_PTRACE,
+		syscall.PTRACE_GETREGSET,
+		uintptr(t.tid),
+		linux.NT_ARM_TLS,
+		uintptr(unsafe.Pointer(&iovec)),
+		0, 0)
+	if errno != 0 {
+		return errno
+	}
+	return nil
+}
+
+// setTLS sets the thread local storage register.
+func (t *thread) setTLS(tls *uint64) error {
+	iovec := syscall.Iovec{
+		Base: (*byte)(unsafe.Pointer(tls)),
+		Len:  uint64(unsafe.Sizeof(*tls)),
+	}
+	_, _, errno := syscall.RawSyscall6(
+		syscall.SYS_PTRACE,
+		syscall.PTRACE_SETREGSET,
+		uintptr(t.tid),
+		linux.NT_ARM_TLS,
+		uintptr(unsafe.Pointer(&iovec)),
+		0, 0)
+	if errno != 0 {
+		return errno
+	}
+	return nil
+}

pkg/sentry/platform/ptrace/subprocess.go

@@ -506,6 +506,9 @@ func (s *subprocess) switchToApp(c *context, ac arch.Context) bool {
 	regs := &ac.StateData().Regs
 	t.resetSysemuRegs(regs)
 
+	// Extract TLS register
+	tls := uint64(ac.TLS())
+
 	// Check for interrupts, and ensure that future interrupts will signal t.
 	if !c.interrupt.Enable(t) {
 		// Pending interrupt; simulate.
@@ -526,6 +529,9 @@ func (s *subprocess) switchToApp(c *context, ac arch.Context) bool {
 	if err := t.setFPRegs(fpState, uint64(fpLen), useXsave); err != nil {
 		panic(fmt.Sprintf("ptrace set fpregs (%+v) failed: %v", fpState, err))
 	}
+	if err := t.setTLS(&tls); err != nil {
+		panic(fmt.Sprintf("ptrace set tls (%+v) failed: %v", tls, err))
+	}
 
 	for {
 		// Start running until the next system call.
@@ -555,6 +561,12 @@ func (s *subprocess) switchToApp(c *context, ac arch.Context) bool {
 		if err := t.getFPRegs(fpState, uint64(fpLen), useXsave); err != nil {
 			panic(fmt.Sprintf("ptrace get fpregs failed: %v", err))
 		}
+		if err := t.getTLS(&tls); err != nil {
+			panic(fmt.Sprintf("ptrace get tls failed: %v", err))
+		}
+		if !ac.SetTLS(uintptr(tls)) {
+			panic(fmt.Sprintf("tls value %v is invalid", tls))
+		}
 
 		// Is it a system call?
 		if sig == (syscallEvent | syscall.SIGTRAP) {