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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>
This commit is contained in:
Austin Clements 2014-12-19 16:16:17 -05:00
parent 3ffc9756d1
commit 675eb72c28
17 changed files with 217 additions and 2 deletions

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@ -9,3 +9,4 @@ import "testing"
func TestSetgid(t *testing.T) { testSetgid(t) }
func Test6997(t *testing.T) { test6997(t) }
func TestBuildID(t *testing.T) { testBuildID(t) }
func Test9400(t *testing.T) { test9400(t) }

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@ -0,0 +1,20 @@
#include "textflag.h"
TEXT ·RewindAndSetgid(SB),NOSPLIT,$0-0
// Rewind stack pointer so anything that happens on the stack
// will clobber the test pattern created by the caller
ADDL $(1024 * 8), SP
// Ask signaller to setgid
MOVL $1, ·Baton(SB)
// Wait for setgid completion
loop:
PAUSE
MOVL ·Baton(SB), AX
CMPL AX, $0
JNE loop
// Restore stack
SUBL $(1024 * 8), SP
RET

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@ -0,0 +1,22 @@
// +build amd64 amd64p32
#include "textflag.h"
TEXT ·RewindAndSetgid(SB),NOSPLIT,$0-0
// Rewind stack pointer so anything that happens on the stack
// will clobber the test pattern created by the caller
ADDQ $(1024 * 8), SP
// Ask signaller to setgid
MOVL $1, ·Baton(SB)
// Wait for setgid completion
loop:
PAUSE
MOVL ·Baton(SB), AX
CMPL AX, $0
JNE loop
// Restore stack
SUBQ $(1024 * 8), SP
RET

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@ -0,0 +1,33 @@
#include "textflag.h"
TEXT cas<>(SB),NOSPLIT,$0
MOVW $0xffff0fc0, PC
TEXT ·RewindAndSetgid(SB),NOSPLIT,$-4-0
// Save link register
MOVW R14, R4
// Rewind stack pointer so anything that happens on the stack
// will clobber the test pattern created by the caller
ADD $(1024 * 8), R13
// Ask signaller to setgid
MOVW $·Baton(SB), R2
storeloop:
MOVW 0(R2), R0
MOVW $1, R1
BL cas<>(SB)
BCC storeloop
// Wait for setgid completion
loop:
MOVW $0, R0
MOVW $0, R1
BL cas<>(SB)
BCC loop
// Restore stack
SUB $(1024 * 8), R13
MOVW R4, R14
RET

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@ -0,0 +1,27 @@
// +build ppc64 ppc64le
#include "textflag.h"
TEXT ·RewindAndSetgid(SB),NOSPLIT,$-8-0
// Rewind stack pointer so anything that happens on the stack
// will clobber the test pattern created by the caller
ADD $(1024 * 8), R1
// Ask signaller to setgid
MOVW $1, R3
SYNC
MOVW R3, ·Baton(SB)
// Wait for setgid completion
loop:
SYNC
MOVW ·Baton(SB), R3
CMP R3, $0
// Hint that we're in a spin loop
OR R1, R1, R1
BNE loop
ISYNC
// Restore stack
SUB $(1024 * 8), R1
RET

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@ -0,0 +1,9 @@
// Copyright 2014 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package issue9400
var Baton int32
func RewindAndSetgid()

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@ -0,0 +1,58 @@
// Copyright 2014 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Test that SIGSETXID runs on signal stack, since it's likely to
// overflow if it runs on the Go stack.
package cgotest
/*
#include <sys/types.h>
#include <unistd.h>
*/
import "C"
import (
"runtime"
"sync/atomic"
"testing"
"./issue9400"
)
func test9400(t *testing.T) {
// We synchronize through a shared variable, so we need two procs
defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(2))
// Start signaller
atomic.StoreInt32(&issue9400.Baton, 0)
go func() {
// Wait for RewindAndSetgid
for atomic.LoadInt32(&issue9400.Baton) == 0 {
runtime.Gosched()
}
// Broadcast SIGSETXID
runtime.LockOSThread()
C.setgid(0)
// Indicate that signalling is done
atomic.StoreInt32(&issue9400.Baton, 0)
}()
// Grow the stack and put down a test pattern
const pattern = 0x123456789abcdef
var big [1024]uint64 // len must match assmebly
for i := range big {
big[i] = pattern
}
// Temporarily rewind the stack and trigger SIGSETXID
issue9400.RewindAndSetgid()
// Check test pattern
for i := range big {
if big[i] != pattern {
t.Fatalf("entry %d of test pattern is wrong; %#x != %#x", i, big[i], pattern)
}
}
}

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@ -394,6 +394,10 @@ func setsig(i int32, fn uintptr, restart bool) {
sigaction(uint32(i), &sa, nil)
}
func setsigstack(i int32) {
gothrow("setsigstack")
}
func getsig(i int32) uintptr {
var sa sigactiont
memclr(unsafe.Pointer(&sa), unsafe.Sizeof(sa))

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@ -189,6 +189,10 @@ func setsig(i int32, fn uintptr, restart bool) {
sigaction(i, &sa, nil)
}
func setsigstack(i int32) {
gothrow("setsigstack")
}
func getsig(i int32) uintptr {
var sa sigactiont
sigaction(i, nil, &sa)

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@ -190,6 +190,11 @@ func setsig(i int32, fn uintptr, restart bool) {
sa.sa_handler = fn
sigaction(i, &sa, nil)
}
func setsigstack(i int32) {
gothrow("setsigstack")
}
func getsig(i int32) uintptr {
var sa sigactiont
sigaction(i, nil, &sa)

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@ -246,6 +246,20 @@ func setsig(i int32, fn uintptr, restart bool) {
}
}
func setsigstack(i int32) {
var sa sigactiont
if rt_sigaction(uintptr(i), nil, &sa, unsafe.Sizeof(sa.sa_mask)) != 0 {
gothrow("rt_sigaction failure")
}
if sa.sa_handler == 0 || sa.sa_handler == _SIG_DFL || sa.sa_handler == _SIG_IGN || sa.sa_flags&_SA_ONSTACK != 0 {
return
}
sa.sa_flags |= _SA_ONSTACK
if rt_sigaction(uintptr(i), &sa, nil, unsafe.Sizeof(sa.sa_mask)) != 0 {
gothrow("rt_sigaction failure")
}
}
func getsig(i int32) uintptr {
var sa sigactiont

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@ -233,6 +233,10 @@ func setsig(i int32, fn uintptr, restart bool) {
sigaction(i, &sa, nil)
}
func setsigstack(i int32) {
gothrow("setsigstack")
}
func getsig(i int32) uintptr {
var sa sigactiont
sigaction(i, nil, &sa)

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@ -203,6 +203,10 @@ func setsig(i int32, fn uintptr, restart bool) {
sigaction(i, &sa, nil)
}
func setsigstack(i int32) {
gothrow("setsigstack")
}
func getsig(i int32) uintptr {
var sa sigactiont
sigaction(i, nil, &sa)

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@ -252,6 +252,10 @@ func setsig(i int32, fn uintptr, restart bool) {
sigaction(i, &sa, nil)
}
func setsigstack(i int32) {
gothrow("setsigstack")
}
func getsig(i int32) uintptr {
var sa sigactiont
sigaction(i, nil, &sa)

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@ -372,6 +372,7 @@ const (
_SigHandling = 1 << 5 // our signal handler is registered
_SigIgnored = 1 << 6 // the signal was ignored before we registered for it
_SigGoExit = 1 << 7 // cause all runtime procs to exit (only used on Plan 9).
_SigSetStack = 1 << 8 // add SA_ONSTACK to libc handler
)
// Layout of in-memory per-function information prepared by linker

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@ -37,6 +37,11 @@ func initsig() {
}
}
if t.flags&_SigSetStack != 0 {
setsigstack(i)
continue
}
t.flags |= _SigHandling
setsig(i, funcPC(sighandler), true)
}

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@ -42,8 +42,8 @@ var sigtable = [...]sigTabT{
/* 29 */ {_SigNotify, "SIGIO: i/o now possible"},
/* 30 */ {_SigNotify, "SIGPWR: power failure restart"},
/* 31 */ {_SigNotify, "SIGSYS: bad system call"},
/* 32 */ {0, "signal 32"}, /* SIGCANCEL; see issue 6997 */
/* 33 */ {0, "signal 33"}, /* SIGSETXID; see issue 3871 */
/* 32 */ {_SigSetStack, "signal 32"}, /* SIGCANCEL; see issue 6997 */
/* 33 */ {_SigSetStack, "signal 33"}, /* SIGSETXID; see issue 3871, 9400 */
/* 34 */ {_SigNotify, "signal 34"},
/* 35 */ {_SigNotify, "signal 35"},
/* 36 */ {_SigNotify, "signal 36"},