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From:   Alexander Potapenko <glider@google.com>
Date:   Wed, 3 Aug 2022 19:45:53 +0200
Message-ID: <CAG_fn=ViyCu8uGy5YQ_FdPmsMWzX5UpozfLXiotF_bDu5P70Lw@mail.gmail.com>
Subject: Re: [PATCH v4 11/45] kmsan: add KMSAN runtime core
To:     Marco Elver <elver@google.com>
Cc:     Alexander Viro <viro@zeniv.linux.org.uk>,
        Alexei Starovoitov <ast@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andrey Konovalov <andreyknvl@google.com>,
        Andy Lutomirski <luto@kernel.org>,
        Arnd Bergmann <arnd@arndb.de>, Borislav Petkov <bp@alien8.de>,
        Christoph Hellwig <hch@lst.de>,
        Christoph Lameter <cl@linux.com>,
        David Rientjes <rientjes@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Eric Dumazet <edumazet@google.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        Ilya Leoshkevich <iii@linux.ibm.com>,
        Ingo Molnar <mingo@redhat.com>, Jens Axboe <axboe@kernel.dk>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Kees Cook <keescook@chromium.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Matthew Wilcox <willy@infradead.org>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Pekka Enberg <penberg@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Petr Mladek <pmladek@suse.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Vegard Nossum <vegard.nossum@oracle.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        kasan-dev <kasan-dev@googlegroups.com>,
        Linux Memory Management List <linux-mm@kvack.org>,
        Linux-Arch <linux-arch@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Wed, Jul 13, 2022 at 12:04 PM Marco Elver <elver@google.com> wrote:
>
> On Fri, Jul 01, 2022 at 04:22PM +0200, 'Alexander Potapenko' via kasan-de=
v wrote:
> [...]
> > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> > index 2e24db4bff192..59819e6fa5865 100644
> > --- a/lib/Kconfig.debug
> > +++ b/lib/Kconfig.debug
> > @@ -963,6 +963,7 @@ config DEBUG_STACKOVERFLOW
> >
> >  source "lib/Kconfig.kasan"
> >  source "lib/Kconfig.kfence"
> > +source "lib/Kconfig.kmsan"
> >
> >  endmenu # "Memory Debugging"
> >
> > diff --git a/lib/Kconfig.kmsan b/lib/Kconfig.kmsan
> > new file mode 100644
> > index 0000000000000..8f768d4034e3c
> > --- /dev/null
> > +++ b/lib/Kconfig.kmsan
> > @@ -0,0 +1,50 @@
> > +# SPDX-License-Identifier: GPL-2.0-only
> > +config HAVE_ARCH_KMSAN
> > +     bool
> > +
> > +config HAVE_KMSAN_COMPILER
> > +     # Clang versions <14.0.0 also support -fsanitize=3Dkernel-memory,=
 but not
> > +     # all the features necessary to build the kernel with KMSAN.
> > +     depends on CC_IS_CLANG && CLANG_VERSION >=3D 140000
> > +     def_bool $(cc-option,-fsanitize=3Dkernel-memory -mllvm -msan-disa=
ble-checks=3D1)
> > +
> > +config HAVE_KMSAN_PARAM_RETVAL
> > +     # Separate check for -fsanitize-memory-param-retval support.
>
> This comment doesn't add much value, maybe instead say that "Supported
> only by Clang >=3D 15."
Fixed.

> > +     depends on CC_IS_CLANG && CLANG_VERSION >=3D 140000
>
> Why not just "depends on HAVE_KMSAN_COMPILER"? (All
> fsanitize-memory-param-retval supporting compilers must also be KMSAN
> compilers.)
Good idea, will do.

> > +     def_bool $(cc-option,-fsanitize=3Dkernel-memory -fsanitize-memory=
-param-retval)
> > +
> > +
>
> HAVE_KMSAN_PARAM_RETVAL should be moved under "if KMSAN" so that this
> isn't unnecessarily evaluated in every kernel build (saving 1 shelling
> out to clang in most builds).
Ack.

> > +config KMSAN
> > +     bool "KMSAN: detector of uninitialized values use"
> > +     depends on HAVE_ARCH_KMSAN && HAVE_KMSAN_COMPILER
> > +     depends on SLUB && DEBUG_KERNEL && !KASAN && !KCSAN
> > +     select STACKDEPOT
> > +     select STACKDEPOT_ALWAYS_INIT
> > +     help
> > +       KernelMemorySanitizer (KMSAN) is a dynamic detector of uses of
> > +       uninitialized values in the kernel. It is based on compiler
> > +       instrumentation provided by Clang and thus requires Clang to bu=
ild.
> > +
> > +       An important note is that KMSAN is not intended for production =
use,
> > +       because it drastically increases kernel memory footprint and sl=
ows
> > +       the whole system down.
> > +
> > +       See <file:Documentation/dev-tools/kmsan.rst> for more details.
> > +
> > +if KMSAN
> > +
> > +config KMSAN_CHECK_PARAM_RETVAL
> > +     bool "Check for uninitialized values passed to and returned from =
functions"
> > +     default HAVE_KMSAN_PARAM_RETVAL
>
> This can be enabled even if !HAVE_KMSAN_PARAM_RETVAL. Should this be:
>
>         default y
>         depends on HAVE_KMSAN_PARAM_RETVAL
>
> instead?
>
Ack

--=20
Alexander Potapenko
Software Engineer

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