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https://github.com/golang/go
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runtime: run libc SIGSETXID and SIGCANCEL handlers on signal stack
These signals are used by glibc to broadcast setuid/setgid to all threads and to send pthread cancellations. Unlike other signals, the Go runtime does not intercept these because they must invoke the libc handlers (see issues #3871 and #6997). However, because 1) these signals may be issued asynchronously by a thread running C code to another thread running Go code and 2) glibc does not set SA_ONSTACK for its handlers, glibc's signal handler may be run on a Go stack. Signal frames range from 1.5K on amd64 to many kilobytes on ppc64, so this may overflow the Go stack and corrupt heap (or other stack) data. Fix this by ensuring that these signal handlers have the SA_ONSTACK flag (but not otherwise taking over the handler). This has been a problem since Go 1.1, but it's likely that people haven't encountered it because it only affects setuid/setgid and pthread_cancel. Fixes #9600. Change-Id: I6cf5f5c2d3aa48998d632f61f1ddc2778dcfd300 Reviewed-on: https://go-review.googlesource.com/1887 Reviewed-by: Ian Lance Taylor <iant@golang.org>
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@ -9,3 +9,4 @@ import "testing"
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func TestSetgid(t *testing.T) { testSetgid(t) }
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func Test6997(t *testing.T) { test6997(t) }
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func TestBuildID(t *testing.T) { testBuildID(t) }
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func Test9400(t *testing.T) { test9400(t) }
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20
misc/cgo/test/issue9400/asm_386.s
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20
misc/cgo/test/issue9400/asm_386.s
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@ -0,0 +1,20 @@
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#include "textflag.h"
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TEXT ·RewindAndSetgid(SB),NOSPLIT,$0-0
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// Rewind stack pointer so anything that happens on the stack
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// will clobber the test pattern created by the caller
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ADDL $(1024 * 8), SP
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// Ask signaller to setgid
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MOVL $1, ·Baton(SB)
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// Wait for setgid completion
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loop:
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PAUSE
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MOVL ·Baton(SB), AX
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CMPL AX, $0
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JNE loop
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// Restore stack
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SUBL $(1024 * 8), SP
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RET
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22
misc/cgo/test/issue9400/asm_amd64x.s
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22
misc/cgo/test/issue9400/asm_amd64x.s
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@ -0,0 +1,22 @@
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// +build amd64 amd64p32
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#include "textflag.h"
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TEXT ·RewindAndSetgid(SB),NOSPLIT,$0-0
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// Rewind stack pointer so anything that happens on the stack
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// will clobber the test pattern created by the caller
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ADDQ $(1024 * 8), SP
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// Ask signaller to setgid
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MOVL $1, ·Baton(SB)
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// Wait for setgid completion
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loop:
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PAUSE
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MOVL ·Baton(SB), AX
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CMPL AX, $0
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JNE loop
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// Restore stack
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SUBQ $(1024 * 8), SP
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RET
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33
misc/cgo/test/issue9400/asm_arm.s
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33
misc/cgo/test/issue9400/asm_arm.s
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@ -0,0 +1,33 @@
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#include "textflag.h"
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TEXT cas<>(SB),NOSPLIT,$0
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MOVW $0xffff0fc0, PC
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TEXT ·RewindAndSetgid(SB),NOSPLIT,$-4-0
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// Save link register
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MOVW R14, R4
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// Rewind stack pointer so anything that happens on the stack
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// will clobber the test pattern created by the caller
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ADD $(1024 * 8), R13
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// Ask signaller to setgid
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MOVW $·Baton(SB), R2
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storeloop:
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MOVW 0(R2), R0
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MOVW $1, R1
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BL cas<>(SB)
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BCC storeloop
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// Wait for setgid completion
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loop:
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MOVW $0, R0
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MOVW $0, R1
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BL cas<>(SB)
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BCC loop
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// Restore stack
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SUB $(1024 * 8), R13
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MOVW R4, R14
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RET
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27
misc/cgo/test/issue9400/asm_ppc64x.s
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27
misc/cgo/test/issue9400/asm_ppc64x.s
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@ -0,0 +1,27 @@
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// +build ppc64 ppc64le
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#include "textflag.h"
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TEXT ·RewindAndSetgid(SB),NOSPLIT,$-8-0
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// Rewind stack pointer so anything that happens on the stack
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// will clobber the test pattern created by the caller
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ADD $(1024 * 8), R1
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// Ask signaller to setgid
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MOVW $1, R3
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SYNC
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MOVW R3, ·Baton(SB)
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// Wait for setgid completion
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loop:
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SYNC
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MOVW ·Baton(SB), R3
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CMP R3, $0
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// Hint that we're in a spin loop
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OR R1, R1, R1
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BNE loop
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ISYNC
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// Restore stack
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SUB $(1024 * 8), R1
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RET
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9
misc/cgo/test/issue9400/stubs.go
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9
misc/cgo/test/issue9400/stubs.go
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@ -0,0 +1,9 @@
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// Copyright 2014 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package issue9400
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var Baton int32
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func RewindAndSetgid()
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58
misc/cgo/test/issue9400_linux.go
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58
misc/cgo/test/issue9400_linux.go
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@ -0,0 +1,58 @@
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// Copyright 2014 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Test that SIGSETXID runs on signal stack, since it's likely to
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// overflow if it runs on the Go stack.
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package cgotest
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/*
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#include <sys/types.h>
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#include <unistd.h>
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*/
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import "C"
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import (
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"runtime"
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"sync/atomic"
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"testing"
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"./issue9400"
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)
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func test9400(t *testing.T) {
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// We synchronize through a shared variable, so we need two procs
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defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(2))
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// Start signaller
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atomic.StoreInt32(&issue9400.Baton, 0)
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go func() {
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// Wait for RewindAndSetgid
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for atomic.LoadInt32(&issue9400.Baton) == 0 {
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runtime.Gosched()
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}
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// Broadcast SIGSETXID
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runtime.LockOSThread()
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C.setgid(0)
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// Indicate that signalling is done
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atomic.StoreInt32(&issue9400.Baton, 0)
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}()
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// Grow the stack and put down a test pattern
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const pattern = 0x123456789abcdef
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var big [1024]uint64 // len must match assmebly
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for i := range big {
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big[i] = pattern
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}
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// Temporarily rewind the stack and trigger SIGSETXID
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issue9400.RewindAndSetgid()
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// Check test pattern
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for i := range big {
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if big[i] != pattern {
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t.Fatalf("entry %d of test pattern is wrong; %#x != %#x", i, big[i], pattern)
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}
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}
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}
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@ -394,6 +394,10 @@ func setsig(i int32, fn uintptr, restart bool) {
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sigaction(uint32(i), &sa, nil)
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}
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func setsigstack(i int32) {
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gothrow("setsigstack")
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}
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func getsig(i int32) uintptr {
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var sa sigactiont
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memclr(unsafe.Pointer(&sa), unsafe.Sizeof(sa))
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@ -189,6 +189,10 @@ func setsig(i int32, fn uintptr, restart bool) {
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sigaction(i, &sa, nil)
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}
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func setsigstack(i int32) {
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gothrow("setsigstack")
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}
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func getsig(i int32) uintptr {
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var sa sigactiont
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sigaction(i, nil, &sa)
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@ -190,6 +190,11 @@ func setsig(i int32, fn uintptr, restart bool) {
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sa.sa_handler = fn
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sigaction(i, &sa, nil)
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}
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func setsigstack(i int32) {
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gothrow("setsigstack")
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}
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func getsig(i int32) uintptr {
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var sa sigactiont
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sigaction(i, nil, &sa)
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@ -246,6 +246,20 @@ func setsig(i int32, fn uintptr, restart bool) {
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}
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}
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func setsigstack(i int32) {
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var sa sigactiont
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if rt_sigaction(uintptr(i), nil, &sa, unsafe.Sizeof(sa.sa_mask)) != 0 {
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gothrow("rt_sigaction failure")
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}
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if sa.sa_handler == 0 || sa.sa_handler == _SIG_DFL || sa.sa_handler == _SIG_IGN || sa.sa_flags&_SA_ONSTACK != 0 {
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return
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}
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sa.sa_flags |= _SA_ONSTACK
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if rt_sigaction(uintptr(i), &sa, nil, unsafe.Sizeof(sa.sa_mask)) != 0 {
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gothrow("rt_sigaction failure")
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}
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}
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func getsig(i int32) uintptr {
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var sa sigactiont
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@ -233,6 +233,10 @@ func setsig(i int32, fn uintptr, restart bool) {
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sigaction(i, &sa, nil)
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}
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func setsigstack(i int32) {
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gothrow("setsigstack")
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}
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func getsig(i int32) uintptr {
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var sa sigactiont
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sigaction(i, nil, &sa)
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@ -203,6 +203,10 @@ func setsig(i int32, fn uintptr, restart bool) {
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sigaction(i, &sa, nil)
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}
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func setsigstack(i int32) {
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gothrow("setsigstack")
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}
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func getsig(i int32) uintptr {
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var sa sigactiont
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sigaction(i, nil, &sa)
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sigaction(i, &sa, nil)
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}
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func setsigstack(i int32) {
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gothrow("setsigstack")
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}
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func getsig(i int32) uintptr {
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var sa sigactiont
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sigaction(i, nil, &sa)
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@ -372,6 +372,7 @@ const (
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_SigHandling = 1 << 5 // our signal handler is registered
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_SigIgnored = 1 << 6 // the signal was ignored before we registered for it
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_SigGoExit = 1 << 7 // cause all runtime procs to exit (only used on Plan 9).
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_SigSetStack = 1 << 8 // add SA_ONSTACK to libc handler
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)
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// Layout of in-memory per-function information prepared by linker
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@ -37,6 +37,11 @@ func initsig() {
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}
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}
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if t.flags&_SigSetStack != 0 {
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setsigstack(i)
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continue
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}
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t.flags |= _SigHandling
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setsig(i, funcPC(sighandler), true)
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}
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@ -42,8 +42,8 @@ var sigtable = [...]sigTabT{
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/* 29 */ {_SigNotify, "SIGIO: i/o now possible"},
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/* 30 */ {_SigNotify, "SIGPWR: power failure restart"},
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/* 31 */ {_SigNotify, "SIGSYS: bad system call"},
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/* 32 */ {0, "signal 32"}, /* SIGCANCEL; see issue 6997 */
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/* 33 */ {0, "signal 33"}, /* SIGSETXID; see issue 3871 */
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/* 32 */ {_SigSetStack, "signal 32"}, /* SIGCANCEL; see issue 6997 */
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/* 33 */ {_SigSetStack, "signal 33"}, /* SIGSETXID; see issue 3871, 9400 */
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/* 34 */ {_SigNotify, "signal 34"},
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/* 35 */ {_SigNotify, "signal 35"},
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/* 36 */ {_SigNotify, "signal 36"},
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