linux-kernel - [PATCH 38/43] x86: fs: kmsan: disable CONFIG_DCACHE_WORD

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Message-Id: <20211214162050.660953-39-glider@google.com>
Date:   Tue, 14 Dec 2021 17:20:45 +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,
        Andrey Konovalov <andreyknvl@...il.com>
Subject: [PATCH 38/43] x86: fs: kmsan: disable CONFIG_DCACHE_WORD_ACCESS

dentry_string_cmp() calls read_word_at_a_time(), which might read
uninitialized bytes to optimize string comparisons.
Disabling CONFIG_DCACHE_WORD_ACCESS should prohibit this optimization,
as well as (probably) similar ones.

Suggested-by: Andrey Konovalov <andreyknvl@...il.com>
Signed-off-by: Alexander Potapenko <glider@...gle.com>
---
Link: https://linux-review.googlesource.com/id/I4c0073224ac2897cafb8c037362c49dda9cfa133
---
 arch/x86/Kconfig | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 760570ff3f3e4..0dc77352bc3c9 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -125,7 +125,9 @@ config X86
 	select CLKEVT_I8253
 	select CLOCKSOURCE_VALIDATE_LAST_CYCLE
 	select CLOCKSOURCE_WATCHDOG
-	select DCACHE_WORD_ACCESS
+	# Word-size accesses may read uninitialized data past the trailing \0
+	# in strings and cause false KMSAN reports.
+	select DCACHE_WORD_ACCESS		if !KMSAN
 	select DYNAMIC_SIGFRAME
 	select EDAC_ATOMIC_SCRUB
 	select EDAC_SUPPORT
-- 
2.34.1.173.g76aa8bc2d0-goog