linux-kernel - [PATCH 5.1 50/85] kasan: initialize tag to 0xff in __kasan

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Message-Id: <20190607153855.112480800@linuxfoundation.org>
Date:   Fri,  7 Jun 2019 17:39:35 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Nathan Chancellor <natechancellor@...il.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 5.1 50/85] kasan: initialize tag to 0xff in __kasan_kmalloc

From: Nathan Chancellor <natechancellor@...il.com>

commit 0600597c854e53d2f9b7a6a718c1da2b8b4cb4db upstream.

When building with -Wuninitialized and CONFIG_KASAN_SW_TAGS unset, Clang
warns:

mm/kasan/common.c:484:40: warning: variable 'tag' is uninitialized when
used here [-Wuninitialized]
        kasan_unpoison_shadow(set_tag(object, tag), size);
                                              ^~~

set_tag ignores tag in this configuration but clang doesn't realize it at
this point in its pipeline, as it points to arch_kasan_set_tag as being
the point where it is used, which will later be expanded to (void
*)(object) without a use of tag.  Initialize tag to 0xff, as it removes
this warning and doesn't change the meaning of the code.

Link: https://github.com/ClangBuiltLinux/linux/issues/465
Link: http://lkml.kernel.org/r/20190502163057.6603-1-natechancellor@gmail.com
Fixes: 7f94ffbc4c6a ("kasan: add hooks implementation for tag-based mode")
Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
Reviewed-by: Andrey Konovalov <andreyknvl@...gle.com>
Reviewed-by: Andrey Ryabinin <aryabinin@...tuozzo.com>
Cc: Alexander Potapenko <glider@...gle.com>
Cc: Dmitry Vyukov <dvyukov@...gle.com>
Cc: Nick Desaulniers <ndesaulniers@...gle.com>
Cc: <stable@...r.kernel.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 mm/kasan/common.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -472,7 +472,7 @@ static void *__kasan_kmalloc(struct kmem
 {
 	unsigned long redzone_start;
 	unsigned long redzone_end;
-	u8 tag;
+	u8 tag = 0xff;
 
 	if (gfpflags_allow_blocking(flags))
 		quarantine_reduce();