linux-kernel - [PATCH v2 3/5] kasan: added functions for unpoisoning stack variables

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Date:   Wed, 29 Nov 2017 13:50:48 -0800
From:   Paul Lawrence <paullawrence@...gle.com>
To:     Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Michal Marek <mmarek@...e.com>
Cc:     linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com,
        linux-mm@...ck.org, linux-kbuild@...r.kernel.org,
        Matthias Kaehlcke <mka@...omium.org>,
        Michael Davidson <md@...gle.com>,
        Greg Hackmann <ghackmann@...gle.com>,
        Paul Lawrence <paullawrence@...gle.com>
Subject: [PATCH v2 3/5] kasan: added functions for unpoisoning stack variables

From: Alexander Potapenko <glider@...gle.com>

As a code-size optimization, LLVM builds since r279383 may
bulk-manipulate the shadow region when (un)poisoning large memory
blocks.  This requires new callbacks that simply do an uninstrumented
memset().

This fixes linking the Clang-built kernel when using KASAN.

Signed-off-by: Alexander Potapenko <glider@...gle.com>
[ghackmann@...gle.com: fix memset() parameters, and tweak
 commit message to describe new callbacks]
Signed-off-by: Greg Hackmann <ghackmann@...gle.com>
Signed-off-by: Paul Lawrence <paullawrence@...gle.com>

---
 mm/kasan/kasan.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c
index f86f862f41f8..89565a1ec417 100644
--- a/mm/kasan/kasan.c
+++ b/mm/kasan/kasan.c
@@ -768,6 +768,21 @@ void __asan_allocas_unpoison(const void *stack_top, const void *stack_bottom)
 }
 EXPORT_SYMBOL(__asan_allocas_unpoison);
 
+/* Emitted by the compiler to [un]poison local variables. */
+#define DEFINE_ASAN_SET_SHADOW(byte) \
+	void __asan_set_shadow_##byte(const void *addr, size_t size)	\
+	{								\
+		__memset((void *)addr, 0x##byte, size);			\
+	}								\
+	EXPORT_SYMBOL(__asan_set_shadow_##byte)
+
+DEFINE_ASAN_SET_SHADOW(00);
+DEFINE_ASAN_SET_SHADOW(f1);
+DEFINE_ASAN_SET_SHADOW(f2);
+DEFINE_ASAN_SET_SHADOW(f3);
+DEFINE_ASAN_SET_SHADOW(f5);
+DEFINE_ASAN_SET_SHADOW(f8);
+
 #ifdef CONFIG_MEMORY_HOTPLUG
 static int __meminit kasan_mem_notifier(struct notifier_block *nb,
 			unsigned long action, void *data)
-- 
2.15.0.531.g2ccb3012c9-goog