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runtime: remap stack spans with MAP_STACK on OpenBSD

OpenBSD 6.4 is going to start requiring that the SP points to memory
that was mapped with MAP_STACK on system call entry, traps, and when
switching to the alternate signal stack [1]. Currently, Go doesn't map
any memory MAP_STACK, so the kernel quickly kills Go processes.

Fix this by remapping the memory that backs stack spans with
MAP_STACK, and re-remapping it without MAP_STACK when it's returned to
the heap.

[1] http://openbsd-archive.7691.n7.nabble.com/stack-register-checking-td338238.html

Fixes #26142.

Change-Id: I656eb84385a22833445d49328bb304f8cdd0e225
Reviewed-on: https://go-review.googlesource.com/121657
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
This commit is contained in:
Austin Clements 2018-06-29 14:56:48 -04:00
parent a94a390e5c
commit 955cc07dde
7 changed files with 74 additions and 0 deletions

View File

@ -37,6 +37,7 @@ const (
MAP_ANON = C.MAP_ANON
MAP_PRIVATE = C.MAP_PRIVATE
MAP_FIXED = C.MAP_FIXED
MAP_STACK = C.MAP_STACK
MADV_FREE = C.MADV_FREE

View File

@ -17,6 +17,7 @@ const (
_MAP_ANON = 0x1000
_MAP_PRIVATE = 0x2
_MAP_FIXED = 0x10
_MAP_STACK = 0x4000
_MADV_FREE = 0x6

View File

@ -17,6 +17,7 @@ const (
_MAP_ANON = 0x1000
_MAP_PRIVATE = 0x2
_MAP_FIXED = 0x10
_MAP_STACK = 0x4000
_MADV_FREE = 0x6

View File

@ -17,6 +17,7 @@ const (
_MAP_ANON = 0x1000
_MAP_PRIVATE = 0x2
_MAP_FIXED = 0x10
_MAP_STACK = 0x4000
_MADV_FREE = 0x6

View File

@ -0,0 +1,17 @@
// Copyright 2018 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.
// +build !openbsd
package runtime
// osStackAlloc performs OS-specific initialization before s is used
// as stack memory.
func osStackAlloc(s *mspan) {
}
// osStackFree undoes the effect of osStackAlloc before s is returned
// to the heap.
func osStackFree(s *mspan) {
}

View File

@ -80,6 +80,9 @@ var sigset_all = ^sigset(0)
// From OpenBSD's <sys/sysctl.h>
const (
_CTL_KERN = 1
_KERN_OSREV = 3
_CTL_HW = 6
_HW_NCPU = 3
_HW_PAGESIZE = 7
@ -109,6 +112,17 @@ func getPageSize() uintptr {
return 0
}
func getOSRev() int32 {
mib := [2]uint32{_CTL_KERN, _KERN_OSREV}
out := uint32(0)
nout := unsafe.Sizeof(out)
ret := sysctl(&mib[0], 2, (*byte)(unsafe.Pointer(&out)), &nout, nil, 0)
if ret >= 0 {
return int32(out)
}
return 0
}
//go:nosplit
func semacreate(mp *m) {
}
@ -194,6 +208,7 @@ func newosproc(mp *m) {
func osinit() {
ncpu = getncpu()
physPageSize = getPageSize()
haveMapStack = getOSRev() >= 201805 // OpenBSD 6.3
}
var urandom_dev = []byte("/dev/urandom\x00")
@ -286,3 +301,35 @@ func sigdelset(mask *sigset, i int) {
func (c *sigctxt) fixsigcode(sig uint32) {
}
var haveMapStack = false
func osStackAlloc(s *mspan) {
// OpenBSD 6.4+ requires that stacks be mapped with MAP_STACK.
// It will check this on entry to system calls, traps, and
// when switching to the alternate system stack.
//
// This function is called before s is used for any data, so
// it's safe to simply re-map it.
osStackRemap(s, _MAP_STACK)
}
func osStackFree(s *mspan) {
// Undo MAP_STACK.
osStackRemap(s, 0)
}
func osStackRemap(s *mspan, flags int32) {
if !haveMapStack {
// OpenBSD prior to 6.3 did not have MAP_STACK and so
// the following mmap will fail. But it also didn't
// require MAP_STACK (obviously), so there's no need
// to do the mmap.
return
}
a, err := mmap(unsafe.Pointer(s.base()), s.npages*pageSize, _PROT_READ|_PROT_WRITE, _MAP_PRIVATE|_MAP_ANON|_MAP_FIXED|flags, -1, 0)
if err != 0 || uintptr(a) != s.base() {
print("runtime: remapping stack memory ", hex(s.base()), " ", s.npages*pageSize, " a=", a, " err=", err, "\n")
throw("remapping stack memory failed")
}
}

View File

@ -186,6 +186,7 @@ func stackpoolalloc(order uint8) gclinkptr {
if s.manualFreeList.ptr() != nil {
throw("bad manualFreeList")
}
osStackAlloc(s)
s.elemsize = _FixedStack << order
for i := uintptr(0); i < _StackCacheSize; i += s.elemsize {
x := gclinkptr(s.base() + i)
@ -238,6 +239,7 @@ func stackpoolfree(x gclinkptr, order uint8) {
// By not freeing, we prevent step #4 until GC is done.
stackpool[order].remove(s)
s.manualFreeList = 0
osStackFree(s)
mheap_.freeManual(s, &memstats.stacks_inuse)
}
}
@ -385,6 +387,7 @@ func stackalloc(n uint32) stack {
if s == nil {
throw("out of memory")
}
osStackAlloc(s)
s.elemsize = uintptr(n)
}
v = unsafe.Pointer(s.base())
@ -463,6 +466,7 @@ func stackfree(stk stack) {
if gcphase == _GCoff {
// Free the stack immediately if we're
// sweeping.
osStackFree(s)
mheap_.freeManual(s, &memstats.stacks_inuse)
} else {
// If the GC is running, we can't return a
@ -1112,6 +1116,7 @@ func freeStackSpans() {
if s.allocCount == 0 {
list.remove(s)
s.manualFreeList = 0
osStackFree(s)
mheap_.freeManual(s, &memstats.stacks_inuse)
}
s = next
@ -1126,6 +1131,7 @@ func freeStackSpans() {
for s := stackLarge.free[i].first; s != nil; {
next := s.next
stackLarge.free[i].remove(s)
osStackFree(s)
mheap_.freeManual(s, &memstats.stacks_inuse)
s = next
}