[Docs] Use proper headling levels in CFI doc.

[samsonov]

Summary

Before that, all sections were considered a subsection of
"Introduction".

[Docs] Move the list of CFI schemes down to CFI doc, and update it.

[pcc]

docs/ControlFlowIntegrity.rst

23 ↗

(On Diff #41895)

This sentence was a little confusing, as it implies that only a subset of schemes are supported. Maybe "You can also enable a subset of available schemes by following [these instructions]."

78 ↗

(On Diff #41895)

This should also be updated I suppose?

183 ↗

(On Diff #41895)

Likewise

[samsonov]

• Address pcc's comments.

docs/ControlFlowIntegrity.rst

23 ↗

(On Diff #41895)

Fixed. Let me know if you want instructions to be more verbose.

[pcc]

LGTM

cfe/trunk/docs/ControlFlowIntegrity.rst

 
 Clang includes an implementation of a number of control flow integrity (CFI)
 schemes, which are designed to abort the program upon detecting certain forms
 of undefined behavior that can potentially allow attackers to subvert the
 program's control flow. These schemes have been optimized for performance,
 allowing developers to enable them in release builds.
 
 To enable Clang's available CFI schemes, use the flag ``-fsanitize=cfi``.
-As currently implemented, all of Clang's CFI schemes (``cfi-vcall``,
-``cfi-derived-cast``, ``cfi-unrelated-cast``, ``cfi-nvcall``, ``cfi-icall``)
-rely on link-time optimization (LTO); so it is required to specify
-``-flto``, and the linker used must support LTO, for example via the `gold
-plugin`_. To allow the checks to be implemented efficiently, the program must
+You can also enable a subset of available :ref:`schemes <cfi-schemes>`.
+As currently implemented, all schemes rely on link-time optimization (LTO);
+so it is required to specify ``-flto``, and the linker used must support LTO,
+for example via the `gold plugin`_.
+To allow the checks to be implemented efficiently, the program must
 be structured such that certain object files are compiled with CFI enabled,
 and are statically linked into the program. This may preclude the use of
 shared libraries in some cases.
 
-Clang currently implements forward-edge CFI for member function calls and
-bad cast checking. More schemes are under development.
-
 .. _gold plugin: http://llvm.org/docs/GoldPlugin.html
 
+.. _cfi-schemes:
+
+Available schemes
+=================
+
+Available schemes are:
+
+  -  ``-fsanitize=cfi-cast-strict``: Enables :ref:`strict cast checks
+     <cfi-strictness>`.
+  -  ``-fsanitize=cfi-derived-cast``: Base-to-derived cast to the wrong
+     dynamic type.
+  -  ``-fsanitize=cfi-unrelated-cast``: Cast from ``void*`` or another
+     unrelated type to the wrong dynamic type.
+  -  ``-fsanitize=cfi-nvcall``: Non-virtual call via an object whose vptr is of
+     the wrong dynamic type.
+  -  ``-fsanitize=cfi-vcall``: Virtual call via an object whose vptr is of the
+     wrong dynamic type.
+  -  ``-fsanitize=cfi-icall``: Indirect call of a function with wrong dynamic
+     type.
+
+You can use ``-fsanitize=cfi`` to enable all the schemes and use
+``-fno-sanitize`` flag to narrow down the set of schemes as desired.
+For example, you can build your program with
+``-fsanitize=cfi -fno-sanitize=cfi-nvcall,cfi-icall``
+to use all schemes except for non-virtual member function call and indirect call
+checking.
+
+Remember that you have to provide ``-flto`` if at least one CFI scheme is
+enabled.
+
+
 Forward-Edge CFI for Virtual Calls
-----------------------------------
+==================================
 
 This scheme checks that virtual calls take place using a vptr of the correct
 dynamic type; that is, the dynamic type of the called object must be a
 derived class of the static type of the object used to make the call.
 This CFI scheme can be enabled on its own using ``-fsanitize=cfi-vcall``.
 
 For this scheme to work, all translation units containing the definition
 of a virtual member function (whether inline or not), other than members
 of :ref:`blacklisted <cfi-blacklist>` types, must be compiled with
 ``-fsanitize=cfi-vcall`` enabled and be statically linked into the program.
 
 Performance
-~~~~~~~~~~~
+-----------
 
 A performance overhead of less than 1% has been measured by running the
 Dromaeo benchmark suite against an instrumented version of the Chromium
 web browser. Another good performance benchmark for this mechanism is the
 virtual-call-heavy SPEC 2006 xalancbmk.
 
 Note that this scheme has not yet been optimized for binary size; an increase
 of up to 15% has been observed for Chromium.
 
 Bad Cast Checking
------------------
+=================
 
 This scheme checks that pointer casts are made to an object of the correct
 dynamic type; that is, the dynamic type of the object must be a derived class
 of the pointee type of the cast. The checks are currently only introduced
 where the class being casted to is a polymorphic class.
 
 Bad casts are not in themselves control flow integrity violations, but they
 can also create security vulnerabilities, and the implementation uses many

 
 For this scheme to work, all translation units containing the definition
 of a virtual member function (whether inline or not), other than members
 of :ref:`blacklisted <cfi-blacklist>` types, must be compiled with
 ``-fsanitize=cfi-derived-cast`` or ``-fsanitize=cfi-unrelated-cast`` enabled
 and be statically linked into the program.
 
 Non-Virtual Member Function Call Checking
------------------------------------------
+=========================================
 
 This scheme checks that non-virtual calls take place using an object of
 the correct dynamic type; that is, the dynamic type of the called object
 must be a derived class of the static type of the object used to make the
 call. The checks are currently only introduced where the object is of a
 polymorphic class type.  This CFI scheme can be enabled on its own using
 ``-fsanitize=cfi-nvcall``.
 
 For this scheme to work, all translation units containing the definition
 of a virtual member function (whether inline or not), other than members
 of :ref:`blacklisted <cfi-blacklist>` types, must be compiled with
 ``-fsanitize=cfi-nvcall`` enabled and be statically linked into the program.
 
 .. _cfi-strictness:
 
 Strictness
-~~~~~~~~~~
+----------
 
 If a class has a single non-virtual base and does not introduce or override
 virtual member functions or fields other than an implicitly defined virtual
 destructor, it will have the same layout and virtual function semantics as
 its base. By default, casts to such classes are checked as if they were made
 to the least derived such class.
 
 Casting an instance of a base class to such a derived class is technically
 undefined behavior, but it is a relatively common hack for introducing
 member functions on class instances with specific properties that works under
 most compilers and should not have security implications, so we allow it by
 default. It can be disabled with ``-fsanitize=cfi-cast-strict``.
 
 Indirect Function Call Checking
--------------------------------
+===============================
 
 This scheme checks that function calls take place using a function of the
 correct dynamic type; that is, the dynamic type of the function must match
 the static type used at the call. This CFI scheme can be enabled on its own
 using ``-fsanitize=cfi-icall``.
 
 For this scheme to work, each indirect function call in the program, other
 than calls in :ref:`blacklisted <cfi-blacklist>` functions, must call a

 Each translation unit compiled with ``-fsanitize=cfi-icall`` must be
 statically linked into the program or shared library, and calls across
 shared library boundaries are handled as if the callee was not compiled with
 ``-fsanitize=cfi-icall``.
 
 This scheme is currently only supported on the x86 and x86_64 architectures.
 
 ``-fsanitize=cfi-icall`` and ``-fsanitize=function``
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+----------------------------------------------------
 
 This tool is similar to ``-fsanitize=function`` in that both tools check
 the types of function calls. However, the two tools occupy different points
 on the design space; ``-fsanitize=function`` is a developer tool designed
 to find bugs in local development builds, whereas ``-fsanitize=cfi-icall``
 is a security hardening mechanism designed to be deployed in release builds.
 
 ``-fsanitize=function`` has a higher space and time overhead due to a more
 complex type check at indirect call sites, as well as a need for run-time
 type information (RTTI), which may make it unsuitable for deployment. Because
 of the need for RTTI, ``-fsanitize=function`` can only be used with C++
 programs, whereas ``-fsanitize=cfi-icall`` can protect both C and C++ programs.
 
 On the other hand, ``-fsanitize=function`` conforms more closely with the C++
 standard and user expectations around interaction with shared libraries;
 the identity of function pointers is maintained, and calls across shared
 library boundaries are no different from calls within a single program or
 shared library.
 
 .. _cfi-blacklist:
 
 Blacklist
----------
+=========
 
 A :doc:`SanitizerSpecialCaseList` can be used to relax CFI checks for certain
 source files, functions and types using the ``src``, ``fun`` and ``type``
 entity types.
 
 In addition, if a type has a ``uuid`` attribute and the blacklist contains
 the type entry ``attr:uuid``, CFI checks are suppressed for that type. This
 allows all COM types to be easily blacklisted, which is useful as COM types
 are typically defined outside of the linked program.
 
 .. code-block:: bash
 
     # Suppress checking for code in a file.
     src:bad_file.cpp
     src:bad_header.h
     # Ignore all functions with names containing MyFooBar.
     fun:*MyFooBar*
     # Ignore all types in the standard library.
     type:std::*
     # Ignore all types with a uuid attribute.
     type:attr:uuid
 
 Design
-------
+======
 
 Please refer to the :doc:`design document<ControlFlowIntegrityDesign>`.
 
 Publications
-------------
+============
 
 `Control-Flow Integrity: Principles, Implementations, and Applications <http://research.microsoft.com/pubs/64250/ccs05.pdf>`_.
 Martin Abadi, Mihai Budiu, Úlfar Erlingsson, Jay Ligatti.
 
 `Enforcing Forward-Edge Control-Flow Integrity in GCC & LLVM <http://www.pcc.me.uk/~peter/acad/usenix14.pdf>`_.
 Caroline Tice, Tom Roeder, Peter Collingbourne, Stephen Checkoway,
 Úlfar Erlingsson, Luis Lozano, Geoff Pike.

cfe/trunk/docs/UsersManual.rst

-  ``-fsanitize=dataflow``: :doc:`DataFlowSanitizer`, a general data
       flow analysis.
    -  ``-fsanitize=cfi``: :doc:`control flow integrity <ControlFlowIntegrity>`
       checks. Requires ``-flto``.
    -  ``-fsanitize=safe-stack``: :doc:`safe stack <SafeStack>`
       protection against stack-based memory corruption errors.
 
    There are more fine-grained checks available: see
    the :ref:`list <ubsan-checks>` of specific kinds of
-   undefined behavior that can be detected. Checks for :doc:`ControlFlowIntegrity`
-   are:
-
-   -  ``-fsanitize=cfi-cast-strict``: Enables :ref:`strict cast checks
-      <cfi-strictness>`.
-   -  ``-fsanitize=cfi-derived-cast``: Base-to-derived cast to the wrong
-      dynamic type. Requires ``-flto``.
-   -  ``-fsanitize=cfi-unrelated-cast``: Cast from ``void*`` or another
-      unrelated type to the wrong dynamic type. Requires ``-flto``.
-   -  ``-fsanitize=cfi-nvcall``: Non-virtual call via an object whose vptr is of
-      the wrong dynamic type. Requires ``-flto``.
-   -  ``-fsanitize=cfi-vcall``: Virtual call via an object whose vptr is of the
-      wrong dynamic type. Requires ``-flto``.
+   undefined behavior that can be detected and the :ref:`list <cfi-schemes>`
+   of control flow integrity schemes.
 
    You can turn off or modify checks for certain source files, functions
    or even variables by providing a special file:
 
    -  ``-fsanitize-blacklist=/path/to/blacklist/file``: disable or modify
       sanitizer checks for objects listed in the file. See
       :doc:`SanitizerSpecialCaseList` for file format description.
    -  ``-fno-sanitize-blacklist``: don't use blacklist file, if it was