From 1336af78d5dc2a6bc54d22ed45f4dd4793c2f964 Mon Sep 17 00:00:00 2001
From: Jamie Liu <jamieliu@google.com>
Date: Tue, 6 Oct 2020 13:53:26 -0700
Subject: Implement membarrier(2) commands other than *_SYNC_CORE.

Updates #267

PiperOrigin-RevId: 335713923
---
 pkg/sentry/hostmm/membarrier.go | 90 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 90 insertions(+)
 create mode 100644 pkg/sentry/hostmm/membarrier.go

(limited to 'pkg/sentry/hostmm/membarrier.go')

diff --git a/pkg/sentry/hostmm/membarrier.go b/pkg/sentry/hostmm/membarrier.go
new file mode 100644
index 000000000..4468d75f1
--- /dev/null
+++ b/pkg/sentry/hostmm/membarrier.go
@@ -0,0 +1,90 @@
+// Copyright 2020 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package hostmm
+
+import (
+	"syscall"
+
+	"golang.org/x/sys/unix"
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/log"
+)
+
+var (
+	haveMembarrierGlobal           = false
+	haveMembarrierPrivateExpedited = false
+)
+
+func init() {
+	supported, _, e := syscall.RawSyscall(unix.SYS_MEMBARRIER, linux.MEMBARRIER_CMD_QUERY, 0 /* flags */, 0 /* unused */)
+	if e != 0 {
+		if e != syscall.ENOSYS {
+			log.Warningf("membarrier(MEMBARRIER_CMD_QUERY) failed: %s", e.Error())
+		}
+		return
+	}
+	// We don't use MEMBARRIER_CMD_GLOBAL_EXPEDITED because this sends IPIs to
+	// all CPUs running tasks that have previously invoked
+	// MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED, which presents a DOS risk.
+	// (MEMBARRIER_CMD_GLOBAL is synchronize_rcu(), i.e. it waits for an RCU
+	// grace period to elapse without bothering other CPUs.
+	// MEMBARRIER_CMD_PRIVATE_EXPEDITED sends IPIs only to CPUs running tasks
+	// sharing the caller's MM.)
+	if supported&linux.MEMBARRIER_CMD_GLOBAL != 0 {
+		haveMembarrierGlobal = true
+	}
+	if req := uintptr(linux.MEMBARRIER_CMD_PRIVATE_EXPEDITED | linux.MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED); supported&req == req {
+		if _, _, e := syscall.RawSyscall(unix.SYS_MEMBARRIER, linux.MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED, 0 /* flags */, 0 /* unused */); e != 0 {
+			log.Warningf("membarrier(MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED) failed: %s", e.Error())
+		} else {
+			haveMembarrierPrivateExpedited = true
+		}
+	}
+}
+
+// HaveGlobalMemoryBarrier returns true if GlobalMemoryBarrier is supported.
+func HaveGlobalMemoryBarrier() bool {
+	return haveMembarrierGlobal
+}
+
+// GlobalMemoryBarrier blocks until "all running threads [in the host OS] have
+// passed through a state where all memory accesses to user-space addresses
+// match program order between entry to and return from [GlobalMemoryBarrier]",
+// as for membarrier(2).
+//
+// Preconditions: HaveGlobalMemoryBarrier() == true.
+func GlobalMemoryBarrier() error {
+	if _, _, e := syscall.Syscall(unix.SYS_MEMBARRIER, linux.MEMBARRIER_CMD_GLOBAL, 0 /* flags */, 0 /* unused */); e != 0 {
+		return e
+	}
+	return nil
+}
+
+// HaveProcessMemoryBarrier returns true if ProcessMemoryBarrier is supported.
+func HaveProcessMemoryBarrier() bool {
+	return haveMembarrierPrivateExpedited
+}
+
+// ProcessMemoryBarrier is equivalent to GlobalMemoryBarrier, but only
+// synchronizes with threads sharing a virtual address space (from the host OS'
+// perspective) with the calling thread.
+//
+// Preconditions: HaveProcessMemoryBarrier() == true.
+func ProcessMemoryBarrier() error {
+	if _, _, e := syscall.RawSyscall(unix.SYS_MEMBARRIER, linux.MEMBARRIER_CMD_PRIVATE_EXPEDITED, 0 /* flags */, 0 /* unused */); e != 0 {
+		return e
+	}
+	return nil
+}
-- 
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