linux-kernel - [PATCH 1/7] 2 1-byte checks more safer for memory_is_poisoned

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Message-ID: <20180318125342.4278-2-liuwenliang@huawei.com>
Date:   Sun, 18 Mar 2018 20:53:36 +0800
From:   Abbott Liu <liuwenliang@...wei.com>
To:     <linux@...linux.org.uk>, <aryabinin@...tuozzo.com>,
        <marc.zyngier@....com>, <kstewart@...uxfoundation.org>,
        <gregkh@...uxfoundation.org>, <f.fainelli@...il.com>,
        <liuwenliang@...wei.com>, <akpm@...ux-foundation.org>,
        <afzal.mohd.ma@...il.com>, <alexander.levin@...izon.com>
CC:     <glider@...gle.com>, <dvyukov@...gle.com>,
        <christoffer.dall@...aro.org>, <linux@...musvillemoes.dk>,
        <mawilcox@...rosoft.com>, <pombredanne@...b.com>,
        <ard.biesheuvel@...aro.org>, <vladimir.murzin@....com>,
        <nicolas.pitre@...aro.org>, <tglx@...utronix.de>,
        <thgarnie@...gle.com>, <dhowells@...hat.com>,
        <keescook@...omium.org>, <arnd@...db.de>, <geert@...ux-m68k.org>,
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        <labbott@...hat.com>, <philip@....systems>,
        <grygorii.strashko@...aro.org>, <catalin.marinas@....com>,
        <opendmb@...il.com>, <kirill.shutemov@...ux.intel.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <kasan-dev@...glegroups.com>,
        <kvmarm@...ts.cs.columbia.edu>, <linux-mm@...ck.org>
Subject: [PATCH 1/7] 2 1-byte checks more safer for memory_is_poisoned_16

Because in some architecture(eg. arm) instruction set, non-aligned
access support is not very well, so 2 1-byte checks is more
safer than 1 2-byte check. The impact on performance is small
because 16-byte accesses are not too common.

Cc: Andrey Ryabinin <a.ryabinin@...sung.com>
Reviewed-by: Andrew Morton <akpm@...ux-foundation.org>
Reviewed-by: Russell King - ARM Linux <linux@...linux.org.uk>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Acked-by: Dmitry Vyukov <dvyukov@...gle.com>
Signed-off-by: Abbott Liu <liuwenliang@...wei.com>
---
 mm/kasan/kasan.c | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c
index e13d911..104839a 100644
--- a/mm/kasan/kasan.c
+++ b/mm/kasan/kasan.c
@@ -151,13 +151,20 @@ static __always_inline bool memory_is_poisoned_2_4_8(unsigned long addr,
 
 static __always_inline bool memory_is_poisoned_16(unsigned long addr)
 {
-	u16 *shadow_addr = (u16 *)kasan_mem_to_shadow((void *)addr);
-
-	/* Unaligned 16-bytes access maps into 3 shadow bytes. */
-	if (unlikely(!IS_ALIGNED(addr, KASAN_SHADOW_SCALE_SIZE)))
-		return *shadow_addr || memory_is_poisoned_1(addr + 15);
+	u8 *shadow_addr = (u8 *)kasan_mem_to_shadow((void *)addr);
 
-	return *shadow_addr;
+	if (unlikely(shadow_addr[0] || shadow_addr[1])) {
+		return true;
+	} else if (likely(IS_ALIGNED(addr, KASAN_SHADOW_SCALE_SIZE))) {
+		/*
+		 * If two shadow bytes covers 16-byte access, we don't
+		 * need to do anything more. Otherwise, test the last
+		 * shadow byte.
+		 */
+		return false;
+	} else {
+		return memory_is_poisoned_1(addr + 15);
+	}
 }
 
 static __always_inline unsigned long bytes_is_nonzero(const u8 *start,
-- 
2.9.0