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runtime: remap stack spans with MAP_STACK on OpenBSD

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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
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6
src/runtime/stack.go
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
}