Add SeccompSupportDetector for Android.

chrome/browser/android/seccomp_support_detector.cc

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "chrome/browser/android/seccomp_support_detector.h"
+
+#include <sys/utsname.h>
+
+#include "base/message_loop/message_loop_proxy.h"
+#include "base/metrics/histogram_macros.h"
+#include "chrome/common/chrome_utility_messages.h"
+#include "content/public/browser/browser_thread.h"
+#include "content/public/browser/utility_process_host.h"
+
+using content::BrowserThread;
+
+enum AndroidSeccompStatus {

[jln (very slow on Chromium), 2015/03/18 20:49:15]

No enum class?

[Robert Sesek, 2015/03/18 21:41:35]

It doesn't work well with the UMA_HISTOGRAM_ENUMERATION since it tries to +1 the
last value.

+  kDetectionFailed,

[jln (very slow on Chromium), 2015/03/18 20:49:15]

The Chromium appendix to the style guide says to use MACRO_STYLE. I'm happy to
ignore this in new files though.

[Robert Sesek, 2015/03/18 21:41:36]

Ah, yeah I was using the Google style. I'll follow Chromium.

+  kNotSupported,
+  kPrctlSupported,
+  kSyscallSupported,
+  kBothSupported,
+  kLastStatus,
+};
+
+void SeccompSupportDetector::StartDetection() {

[jln (very slow on Chromium), 2015/03/18 20:49:15]

//static?

[Robert Sesek, 2015/03/18 21:41:36]

Done.

+  // This class owns itself. It is created here and the object is released

[jln (very slow on Chromium), 2015/03/18 20:49:15]

"It is created here" -> "An instance is created here" ?

[Robert Sesek, 2015/03/18 21:41:35]

Done.

+  // after seccomp suport is detected.

[jln (very slow on Chromium), 2015/03/18 20:49:15]

The lifetime of this refcounted class is a little complicated. I don't think
"owns itself" captures it.

If I'm following correctly, we guarantee that for a StartDetection() call, there
will be a callback to OnDetectSeccompSupportResult() or OnProcessCrashed() which
will release the particular reference created in StartDetection().

But StartDetection could simply Release() its reference immediately (since the
callback you create also owns a reference).

So why not simply creating a scoped_refptr<..> detector? When StartDetection()
returns, the refcounter should be at one and the object will get deleted when
the various callbacks will be done with it. No need to call Release() from the
On* methods.

[Robert Sesek, 2015/03/18 21:41:35]

I initially did as you suggested and let the Closure own it, but I thought that
was actually less clear. But I do prefer that, so done.

+  SeccompSupportDetector* detector = new SeccompSupportDetector();
+  BrowserThread::PostTask(BrowserThread::FILE, FROM_HERE,
+      base::Bind(&SeccompSupportDetector::DetectKernelVersion, detector));
+}
+
+SeccompSupportDetector::SeccompSupportDetector() {
+}
+
+SeccompSupportDetector::~SeccompSupportDetector() {
+}
+
+void SeccompSupportDetector::DetectKernelVersion() {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+
+  // This method will report the kernel major and minor versions by
+  // taking the lower 16 bits of each version number and combining
+  // it into a 32-bit number.
+
+  // Support known Android kernel versions, and leave room up to 3.50.

[jln (very slow on Chromium), 2015/03/18 20:49:15]

3.20 is actually 4.0

[Robert Sesek, 2015/03/18 21:41:35]

Done.

+  const int kVersionRanges[] = {
+    0x00020006,
+    0x00030000,
+    0x00030003,
+    0x00030004,
+    0x00030008,
+    0x00030010,
+    0x00030014,
+    0x00030017,
+    0x00030018,
+    0x00030050,
+  };
+
+  utsname uts;

[jln (very slow on Chromium), 2015/03/18 20:49:15]

nit: I prefer to use "struct X" for low-level C code, but your choice.

[Robert Sesek, 2015/03/18 21:41:35]

Acknowledged.

+  if (uname(&uts) == 0) {
+    int major, minor;
+    if (sscanf(uts.release, "%d.%d", &major, &minor) == 2) {

[jln (very slow on Chromium), 2015/03/18 20:49:15]

Ok to put all 2.6.X kernels in the same bucket?

For seccomp on Android I don't think it matters indeed.

[Robert Sesek, 2015/03/18 21:41:35]

Yeah, I think so. I don't even know if Chrome runs on any Android devices with a
kernel <3.0.

+      int version = ((major & 0xFFFF) << 16) | (minor & 0xFFFF);
+      UMA_HISTOGRAM_CUSTOM_ENUMERATION(
+          "Android.KernelVersion", version,
+          base::CustomHistogram::ArrayToCustomRanges(
+              kVersionRanges, arraysize(kVersionRanges)));
+    }
+  }
+
+  BrowserThread::PostTask(BrowserThread::IO, FROM_HERE,
+      base::Bind(&SeccompSupportDetector::DetectSeccomp, this));
+}
+
+void SeccompSupportDetector::DetectSeccomp() {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
+
+  content::UtilityProcessHost* utility_process_host =
+      content::UtilityProcessHost::Create(
+          this, base::MessageLoopProxy::current());
+  utility_process_host->Send(new ChromeUtilityMsg_DetectSeccompSupport());
+}
+
+void SeccompSupportDetector::OnProcessCrashed(int exit_code) {
+  UMA_HISTOGRAM_ENUMERATION("Android.SeccompStatus",
+                            kDetectionFailed,
+                            kLastStatus);
+  Release();
+}
+
+bool SeccompSupportDetector::OnMessageReceived(const IPC::Message& message) {
+  bool handled = false;
+  IPC_BEGIN_MESSAGE_MAP(SeccompSupportDetector, message)
+    IPC_MESSAGE_HANDLER(ChromeUtilityHostMsg_DetectSeccompSupport_Result,
+                        OnDetectSeccompSupportResult)
+    IPC_MESSAGE_UNHANDLED(handled = false)
+  IPC_END_MESSAGE_MAP()
+  return handled;
+}
+
+void SeccompSupportDetector::OnDetectSeccompSupportResult(
+    bool prctl_supported, bool syscall_supported) {
+
+  AndroidSeccompStatus status = kNotSupported;
+  if (prctl_supported && syscall_supported)
+    status = kBothSupported;
+  else if (prctl_supported)
+    status = kPrctlSupported;
+  else if (syscall_supported)
+    status = kSyscallSupported;
+
+  UMA_HISTOGRAM_ENUMERATION("Android.SeccompStatus",
+                            status,
+                            kLastStatus);
+
+  Release();
+}