PlatformVerification: Added a check for attestation availability.

Currently if a system is not capable of enrolling for attestation or is
not yet ready to enroll for attestation the flow proceeds to the user
consent dialog anyways. Since user consent is always presented when the
device has not been enrolled the user sees the dialog every time a new
platform verification is initiated (e.g. every video).

This change detects this condition and aborts the verification before
the dialog is shown. Metrics have also been added.

BUG=chromium-os-partner:31591, chromium-os-partner:27593
TEST=unit, manual

Review URL: https://codereview.chromium.org/567723003

Cr-Commit-Position: refs/heads/master@{#297681}

4 files changed, 74 insertions, 1 deletions

diff --git a/chrome/browser/chromeos/attestation/platform_verification_flow.cc b/chrome/browser/chromeos/attestation/platform_verification_flow.cc
index 95cbdc8..cc49b8e 100644
--- a/chrome/browser/chromeos/attestation/platform_verification_flow.cc
+++ b/chrome/browser/chromeos/attestation/platform_verification_flow.cc
@@ -7,6 +7,7 @@
 #include "base/command_line.h"
 #include "base/logging.h"
 #include "base/message_loop/message_loop.h"
+#include "base/metrics/histogram.h"
 #include "base/prefs/pref_service.h"
 #include "base/time/time.h"
 #include "base/timer/timer.h"
@@ -37,6 +38,11 @@ namespace {
 
 const char kDefaultHttpsPort[] = "443";
 const int kTimeoutInSeconds = 8;
+const char kAttestationResultHistogram[] =
+    "ChromeOS.PlatformVerification.Result";
+const char kAttestationAvailableHistogram[] =
+    "ChromeOS.PlatformVerification.Available";
+const int kAttestationResultHistogramMax = 10;
 
 // A callback method to handle DBus errors.
 void DBusCallback(const base::Callback<void(bool)>& on_success,
@@ -56,6 +62,8 @@ void ReportError(
     const chromeos::attestation::PlatformVerificationFlow::ChallengeCallback&
         callback,
     chromeos::attestation::PlatformVerificationFlow::Result error) {
+  UMA_HISTOGRAM_ENUMERATION(kAttestationResultHistogram, error,
+                            kAttestationResultHistogramMax);
   callback.Run(error, std::string(), std::string(), std::string());
 }
 }  // namespace
@@ -182,10 +190,26 @@ void PlatformVerificationFlow::ChallengePlatformKey(
     return;
   }
   ChallengeContext context(web_contents, service_id, challenge, callback);
+  // Check if the device has been prepared to use attestation.
   BoolDBusMethodCallback dbus_callback = base::Bind(
       &DBusCallback,
-      base::Bind(&PlatformVerificationFlow::CheckConsent, this, context),
+      base::Bind(&PlatformVerificationFlow::CheckEnrollment, this, context),
       base::Bind(&ReportError, callback, INTERNAL_ERROR));
+  cryptohome_client_->TpmAttestationIsPrepared(dbus_callback);
+}
+
+void PlatformVerificationFlow::CheckEnrollment(const ChallengeContext& context,
+                                               bool attestation_prepared) {
+  UMA_HISTOGRAM_BOOLEAN(kAttestationAvailableHistogram, attestation_prepared);
+  if (!attestation_prepared) {
+    // This device is not currently able to use attestation features.
+    ReportError(context.callback, PLATFORM_NOT_VERIFIED);
+    return;
+  }
+  BoolDBusMethodCallback dbus_callback = base::Bind(
+      &DBusCallback,
+      base::Bind(&PlatformVerificationFlow::CheckConsent, this, context),
+      base::Bind(&ReportError, context.callback, INTERNAL_ERROR));
   cryptohome_client_->TpmAttestationIsEnrolled(dbus_callback);
 }
 
@@ -352,6 +376,8 @@ void PlatformVerificationFlow::OnChallengeReady(
     return;
   }
   VLOG(1) << "Platform verification successful.";
+  UMA_HISTOGRAM_ENUMERATION(kAttestationResultHistogram, SUCCESS,
+                            kAttestationResultHistogramMax);
   context.callback.Run(SUCCESS,
                        signed_data_pb.data(),
                        signed_data_pb.signature(),
diff --git a/chrome/browser/chromeos/attestation/platform_verification_flow.h b/chrome/browser/chromeos/attestation/platform_verification_flow.h
index b6571a4..a48b11c 100644
--- a/chrome/browser/chromeos/attestation/platform_verification_flow.h
+++ b/chrome/browser/chromeos/attestation/platform_verification_flow.h
@@ -183,6 +183,13 @@ class PlatformVerificationFlow
 
   ~PlatformVerificationFlow();
 
+  // Checks whether the device has already been enrolled for attestation. The
+  // arguments to ChallengePlatformKey are in |context| and
+  // |attestation_prepared| specifies whether attestation has been prepared on
+  // this device.
+  void CheckEnrollment(const ChallengeContext& context,
+                       bool attestation_prepared);
+
   // Checks whether we need to prompt the user for consent before proceeding and
   // invokes the consent UI if so.  The arguments to ChallengePlatformKey are
   // in |context| and |attestation_enrolled| specifies whether attestation has
diff --git a/chrome/browser/chromeos/attestation/platform_verification_flow_unittest.cc b/chrome/browser/chromeos/attestation/platform_verification_flow_unittest.cc
index 609d0b1..ad591c0 100644
--- a/chrome/browser/chromeos/attestation/platform_verification_flow_unittest.cc
+++ b/chrome/browser/chromeos/attestation/platform_verification_flow_unittest.cc
@@ -477,5 +477,14 @@ TEST_F(PlatformVerificationFlowTest, IncognitoMode) {
   EXPECT_EQ(PlatformVerificationFlow::PLATFORM_NOT_VERIFIED, result_);
 }
 
+TEST_F(PlatformVerificationFlowTest, AttestationNotPrepared) {
+  fake_delegate_.set_response(PlatformVerificationFlow::CONSENT_RESPONSE_DENY);
+  fake_cryptohome_client_.set_attestation_enrolled(false);
+  fake_cryptohome_client_.set_attestation_prepared(false);
+  verifier_->ChallengePlatformKey(NULL, kTestID, kTestChallenge, callback_);
+  base::RunLoop().RunUntilIdle();
+  EXPECT_EQ(PlatformVerificationFlow::PLATFORM_NOT_VERIFIED, result_);
+}
+
 }  // namespace attestation
 }  // namespace chromeos
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index 07d1f90..f2740b9 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -2628,6 +2628,24 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="ChromeOS.PlatformVerification.Available"
+    enum="BooleanAvailable">
+  <owner>dkrahn@chromium.org</owner>
+  <summary>
+    Whether platform verification subsystem features are available at the time a
+    platform verification request is made for content protection on Chrome OS.
+  </summary>
+</histogram>
+
+<histogram name="ChromeOS.PlatformVerification.Result"
+    enum="ChromeOSPlatformVerificationResult">
+  <owner>dkrahn@chromium.org</owner>
+  <summary>
+    The result of a platform verification attempt for content protection on
+    Chrome OS.
+  </summary>
+</histogram>
+
 <histogram name="ChromeOS.SAML.APIUsed" enum="BooleanUsage">
   <owner>bartfab@chromium.org</owner>
   <summary>
@@ -39489,6 +39507,19 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <int value="3" label="Reading"/>
 </enum>
 
+<enum name="ChromeOSPlatformVerificationResult" type="int">
+  <summary>
+    Possible results of a platform verification attempt. See
+    chrome/browser/chromeos/attestation/platform_verification.h.
+  </summary>
+  <int value="0" label="Success"/>
+  <int value="1" label="Internal Error"/>
+  <int value="2" label="Platform Not Verified"/>
+  <int value="3" label="Rejected by User"/>
+  <int value="4" label="Rejected by Policy"/>
+  <int value="5" label="Timeout"/>
+</enum>
+
 <enum name="ChromeOSUserImageId" type="int">
   <summary>
     Indices of the default images as defined in