linux-kernel - [PATCH 22/43] kmsan: initialize the output of READ_ONCE

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Date:   Tue, 14 Dec 2021 17:20:29 +0100
From:   Alexander Potapenko <glider@...gle.com>
To:     glider@...gle.com
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
        Christoph Hellwig <hch@....de>,
        Christoph Lameter <cl@...ux.com>,
        David Rientjes <rientjes@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Ilya Leoshkevich <iii@...ux.ibm.com>,
        Ingo Molnar <mingo@...hat.com>, Jens Axboe <axboe@...nel.dk>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Kees Cook <keescook@...omium.org>,
        Marco Elver <elver@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Pekka Enberg <penberg@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Vegard Nossum <vegard.nossum@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 22/43] kmsan: initialize the output of READ_ONCE_NOCHECK()

READ_ONCE_NOCHECK() is already used by KASAN to ignore memory accesses
from e.g. stack unwinders.
Define READ_ONCE_NOCHECK() for KMSAN so that it returns initialized
values. This helps defeat false positives from leftover stack contents.

Signed-off-by: Alexander Potapenko <glider@...gle.com>
---
Link: https://linux-review.googlesource.com/id/I07499eb3e8e59c0ad2fd486cedc932d958b37afd
---
 include/asm-generic/rwonce.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/asm-generic/rwonce.h b/include/asm-generic/rwonce.h
index 8d0a6280e9824..7cf993af8e1ea 100644
--- a/include/asm-generic/rwonce.h
+++ b/include/asm-generic/rwonce.h
@@ -25,6 +25,7 @@
 #include <linux/compiler_types.h>
 #include <linux/kasan-checks.h>
 #include <linux/kcsan-checks.h>
+#include <linux/kmsan-checks.h>
 
 /*
  * Yes, this permits 64-bit accesses on 32-bit architectures. These will
@@ -69,14 +70,14 @@ unsigned long __read_once_word_nocheck(const void *addr)
 
 /*
  * Use READ_ONCE_NOCHECK() instead of READ_ONCE() if you need to load a
- * word from memory atomically but without telling KASAN/KCSAN. This is
+ * word from memory atomically but without telling KASAN/KCSAN/KMSAN. This is
  * usually used by unwinding code when walking the stack of a running process.
  */
 #define READ_ONCE_NOCHECK(x)						\
 ({									\
 	compiletime_assert(sizeof(x) == sizeof(unsigned long),		\
 		"Unsupported access size for READ_ONCE_NOCHECK().");	\
-	(typeof(x))__read_once_word_nocheck(&(x));			\
+	kmsan_init((typeof(x))__read_once_word_nocheck(&(x)));		\
 })
 
 static __no_kasan_or_inline
-- 
2.34.1.173.g76aa8bc2d0-goog