linux-kernel - [PATCH] arm64: Fix warning in mte_get_random

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Date:   Thu, 11 Feb 2021 12:56:02 +0000
From:   Vincenzo Frascino <vincenzo.frascino@....com>
To:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kasan-dev@...glegroups.com
Cc:     Vincenzo Frascino <vincenzo.frascino@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH] arm64: Fix warning in mte_get_random_tag()

The simplification of mte_get_random_tag() caused the introduction of the
warning below:

In file included from arch/arm64/include/asm/kasan.h:9,
                 from include/linux/kasan.h:16,
                 from mm/kasan/common.c:14:
mm/kasan/common.c: In function ‘mte_get_random_tag’:
arch/arm64/include/asm/mte-kasan.h:45:9: warning: ‘addr’ is used
                                         uninitialized [-Wuninitialized]
   45 |         asm(__MTE_PREAMBLE "irg %0, %0"
      |

Fix the warning initializing the address to NULL.

Note: mte_get_random_tag() returns a tag and it never dereferences the address,
hence 'addr' can be safely initialized to NULL.

Fixes: c8f8de4c0887 ("arm64: kasan: simplify and inline MTE functions")
Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Will Deacon <will@...nel.org>
Cc: Andrey Konovalov <andreyknvl@...gle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@....com>
---

This patch is based on linux-next/akpm

 arch/arm64/include/asm/mte-kasan.h | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/mte-kasan.h b/arch/arm64/include/asm/mte-kasan.h
index 3d58489228c0..b2850b750726 100644
--- a/arch/arm64/include/asm/mte-kasan.h
+++ b/arch/arm64/include/asm/mte-kasan.h
@@ -40,7 +40,12 @@ static inline u8 mte_get_mem_tag(void *addr)
 /* Generate a random tag. */
 static inline u8 mte_get_random_tag(void)
 {
-	void *addr;
+	/*
+	 * mte_get_random_tag() returns a tag and it
+	 * never dereferences the address, hence addr
+	 * can be safely initialized to NULL.
+	 */
+	void *addr = NULL;
 
 	asm(__MTE_PREAMBLE "irg %0, %0"
 		: "+r" (addr));
-- 
2.30.0