kmsan: add KMSAN runtime core

For each memory location KernelMemorySanitizer maintains two types of
metadata:

1. The so-called shadow of that location - а byte:byte mapping describing
   whether or not individual bits of memory are initialized (shadow is 0)
   or not (shadow is 1).
2. The origins of that location - а 4-byte:4-byte mapping containing
   4-byte IDs of the stack traces where uninitialized values were
   created.

Each struct page now contains pointers to two struct pages holding KMSAN
metadata (shadow and origins) for the original struct page.  Utility
routines in mm/kmsan/core.c and mm/kmsan/shadow.c handle the metadata
creation, addressing, copying and checking.  mm/kmsan/report.c performs
error reporting in the cases an uninitialized value is used in a way that
leads to undefined behavior.

KMSAN compiler instrumentation is responsible for tracking the metadata
along with the kernel memory.  mm/kmsan/instrumentation.c provides the
implementation for instrumentation hooks that are called from files
compiled with -fsanitize=kernel-memory.

To aid parameter passing (also done at instrumentation level), each
task_struct now contains a struct kmsan_task_state used to track the
metadata of function parameters and return values for that task.

Finally, this patch provides CONFIG_KMSAN that enables KMSAN, and declares
CFLAGS_KMSAN, which are applied to files compiled with KMSAN.  The
KMSAN_SANITIZE:=n Makefile directive can be used to completely disable
KMSAN instrumentation for certain files.

Similarly, KMSAN_ENABLE_CHECKS:=n disables KMSAN checks and makes newly
created stack memory initialized.

Users can also use functions from include/linux/kmsan-checks.h to mark
certain memory regions as uninitialized or initialized (this is called
"poisoning" and "unpoisoning") or check that a particular region is
initialized.

Link: https://lkml.kernel.org/r/20220915150417.722975-12-glider@google.com
Signed-off-by: Alexander Potapenko <glider@google.com>
Acked-by: Marco Elver <elver@google.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Eric Biggers <ebiggers@google.com>
Cc: Eric Biggers <ebiggers@kernel.org>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Ilya Leoshkevich <iii@linux.ibm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vegard Nossum <vegard.nossum@oracle.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

2 files changed, 51 insertions, 0 deletions

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 6d1544d9201e..0129bee7de01 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -970,6 +970,7 @@ 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 000000000000..5b19dbd34d76
--- /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=kernel-memory, but not
+	# all the features necessary to build the kernel with KMSAN.
+	depends on CC_IS_CLANG && CLANG_VERSION >= 140000
+	def_bool $(cc-option,-fsanitize=kernel-memory -mllvm -msan-disable-checks=1)
+
+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 build.
+
+	  An important note is that KMSAN is not intended for production use,
+	  because it drastically increases kernel memory footprint and slows
+	  the whole system down.
+
+	  See <file:Documentation/dev-tools/kmsan.rst> for more details.
+
+if KMSAN
+
+config HAVE_KMSAN_PARAM_RETVAL
+	# -fsanitize-memory-param-retval is supported only by Clang >= 14.
+	depends on HAVE_KMSAN_COMPILER
+	def_bool $(cc-option,-fsanitize=kernel-memory -fsanitize-memory-param-retval)
+
+config KMSAN_CHECK_PARAM_RETVAL
+	bool "Check for uninitialized values passed to and returned from functions"
+	default y
+	depends on HAVE_KMSAN_PARAM_RETVAL
+	help
+	  If the compiler supports -fsanitize-memory-param-retval, KMSAN will
+	  eagerly check every function parameter passed by value and every
+	  function return value.
+
+	  Disabling KMSAN_CHECK_PARAM_RETVAL will result in tracking shadow for
+	  function parameters and return values across function borders. This
+	  is a more relaxed mode, but it generates more instrumentation code and
+	  may potentially report errors in corner cases when non-instrumented
+	  functions call instrumented ones.
+
+endif