[release-branch.go1.16] runtime: keep //go:cgo_unsafe_args arguments alive to prevent GC

When syscall's DLL.FindProc calls into syscall_getprocaddress with a
byte slice pointer, we need to keep those bytes alive. Otherwise the GC
will collect the allocation, and we wind up calling `GetProcAddress` on
garbage, which showed up as various flakes in the builders. It turns out
that this problem extends to many uses of //go:cgo_unsafe_args
throughout, on all platforms. So this patch fixes the issue by keeping
non-integer pointer arguments alive through their invocation in
//go:cgo_unsafe_args functions.

Fixes #49867.
Updates #49731.

Change-Id: I93e4fbc2e8e210cb3fc53149708758bb33f2f9c7
Reviewed-on: https://go-review.googlesource.com/c/go/+/368356
Trust: Jason A. Donenfeld <Jason@zx2c4.com>
Run-TryBot: Jason A. Donenfeld <Jason@zx2c4.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

1 files changed, 31 insertions, 5 deletions

diff --git a/src/runtime/sys_openbsd2.go b/src/runtime/sys_openbsd2.go
index 474e7145e7..5303a68cf5 100644
--- a/src/runtime/sys_openbsd2.go
+++ b/src/runtime/sys_openbsd2.go
@@ -53,6 +53,7 @@ func mmap(addr unsafe.Pointer, n uintptr, prot, flags, fd int32, off uint32) (un
 		ret2            int
 	}{addr, n, prot, flags, fd, off, nil, 0}
 	libcCall(unsafe.Pointer(funcPC(mmap_trampoline)), unsafe.Pointer(&args))
+	KeepAlive(addr) // Just for consistency. Hopefully addr is not a Go address.
 	return args.ret1, args.ret2
 }
 func mmap_trampoline()
@@ -61,6 +62,7 @@ func mmap_trampoline()
 //go:cgo_unsafe_args
 func munmap(addr unsafe.Pointer, n uintptr) {
 	libcCall(unsafe.Pointer(funcPC(munmap_trampoline)), unsafe.Pointer(&addr))
+	KeepAlive(addr) // Just for consistency. Hopefully addr is not a Go address.
 }
 func munmap_trampoline()
 
@@ -68,13 +70,16 @@ func munmap_trampoline()
 //go:cgo_unsafe_args
 func madvise(addr unsafe.Pointer, n uintptr, flags int32) {
 	libcCall(unsafe.Pointer(funcPC(madvise_trampoline)), unsafe.Pointer(&addr))
+	KeepAlive(addr) // Just for consistency. Hopefully addr is not a Go address.
 }
 func madvise_trampoline()
 
 //go:nosplit
 //go:cgo_unsafe_args
 func open(name *byte, mode, perm int32) (ret int32) {
-	return libcCall(unsafe.Pointer(funcPC(open_trampoline)), unsafe.Pointer(&name))
+	ret = libcCall(unsafe.Pointer(funcPC(open_trampoline)), unsafe.Pointer(&name))
+	KeepAlive(name)
+	return
 }
 func open_trampoline()
 
@@ -88,14 +93,18 @@ func close_trampoline()
 //go:nosplit
 //go:cgo_unsafe_args
 func read(fd int32, p unsafe.Pointer, n int32) int32 {
-	return libcCall(unsafe.Pointer(funcPC(read_trampoline)), unsafe.Pointer(&fd))
+	ret := libcCall(unsafe.Pointer(funcPC(read_trampoline)), unsafe.Pointer(&fd))
+	KeepAlive(p)
+	return ret
 }
 func read_trampoline()
 
 //go:nosplit
 //go:cgo_unsafe_args
 func write1(fd uintptr, p unsafe.Pointer, n int32) int32 {
-	return libcCall(unsafe.Pointer(funcPC(write_trampoline)), unsafe.Pointer(&fd))
+	ret := libcCall(unsafe.Pointer(funcPC(write_trampoline)), unsafe.Pointer(&fd))
+	KeepAlive(p)
+	return ret
 }
 func write_trampoline()
 
@@ -118,6 +127,8 @@ func pipe2_trampoline()
 //go:cgo_unsafe_args
 func setitimer(mode int32, new, old *itimerval) {
 	libcCall(unsafe.Pointer(funcPC(setitimer_trampoline)), unsafe.Pointer(&mode))
+	KeepAlive(new)
+	KeepAlive(old)
 }
 func setitimer_trampoline()
 
@@ -131,7 +142,12 @@ func usleep_trampoline()
 //go:nosplit
 //go:cgo_unsafe_args
 func sysctl(mib *uint32, miblen uint32, out *byte, size *uintptr, dst *byte, ndst uintptr) int32 {
-	return libcCall(unsafe.Pointer(funcPC(sysctl_trampoline)), unsafe.Pointer(&mib))
+	ret := libcCall(unsafe.Pointer(funcPC(sysctl_trampoline)), unsafe.Pointer(&mib))
+	KeepAlive(mib)
+	KeepAlive(out)
+	KeepAlive(size)
+	KeepAlive(dst)
+	return ret
 }
 func sysctl_trampoline()
 
@@ -175,7 +191,11 @@ func kqueue_trampoline()
 //go:nosplit
 //go:cgo_unsafe_args
 func kevent(kq int32, ch *keventt, nch int32, ev *keventt, nev int32, ts *timespec) int32 {
-	return libcCall(unsafe.Pointer(funcPC(kevent_trampoline)), unsafe.Pointer(&kq))
+	ret := libcCall(unsafe.Pointer(funcPC(kevent_trampoline)), unsafe.Pointer(&kq))
+	KeepAlive(ch)
+	KeepAlive(ev)
+	KeepAlive(ts)
+	return ret
 }
 func kevent_trampoline()
 
@@ -183,6 +203,8 @@ func kevent_trampoline()
 //go:cgo_unsafe_args
 func sigaction(sig uint32, new *sigactiont, old *sigactiont) {
 	libcCall(unsafe.Pointer(funcPC(sigaction_trampoline)), unsafe.Pointer(&sig))
+	KeepAlive(new)
+	KeepAlive(old)
 }
 func sigaction_trampoline()
 
@@ -190,6 +212,8 @@ func sigaction_trampoline()
 //go:cgo_unsafe_args
 func sigprocmask(how uint32, new *sigset, old *sigset) {
 	libcCall(unsafe.Pointer(funcPC(sigprocmask_trampoline)), unsafe.Pointer(&how))
+	KeepAlive(new)
+	KeepAlive(old)
 }
 func sigprocmask_trampoline()
 
@@ -197,6 +221,8 @@ func sigprocmask_trampoline()
 //go:cgo_unsafe_args
 func sigaltstack(new *stackt, old *stackt) {
 	libcCall(unsafe.Pointer(funcPC(sigaltstack_trampoline)), unsafe.Pointer(&new))
+	KeepAlive(new)
+	KeepAlive(old)
 }
 func sigaltstack_trampoline()