[PATCH master 2/2] tlsf: hardening: skip KASAN checks when zeroing memory

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

We are already unpoisoning the memory before allocation, so we know for
certain that memset will not trip over anything. Switch over to using
__memset in that case to reduce performance impact.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
---
 arch/arm/include/asm/string.h | 8 ++++++++
 common/tlsf.c                 | 8 ++++++--
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/arch/arm/include/asm/string.h b/arch/arm/include/asm/string.h
index f79392e53d01..4b77914865e7 100644
--- a/arch/arm/include/asm/string.h
+++ b/arch/arm/include/asm/string.h
@@ -3,6 +3,8 @@
 #ifndef __ASM_ARM_STRING_H
 #define __ASM_ARM_STRING_H
 
+#include <linux/compiler.h>
+
 #ifdef CONFIG_ARM_OPTIMZED_STRING_FUNCTIONS
 
 #define __HAVE_ARCH_MEMCPY
@@ -17,4 +19,10 @@ extern void *__memcpy(void *, const void *, __kernel_size_t);
 extern void *__memset(void *, int, __kernel_size_t);
 extern void *__memmove(void *, const void *, __kernel_size_t);
 
+static inline void __memzero_explicit(void *s, __kernel_size_t count)
+{
+	__memset(s, 0, count);
+	barrier_data(s);
+}
+
 #endif
diff --git a/common/tlsf.c b/common/tlsf.c
index 01293630dd7c..8666b94ea387 100644
--- a/common/tlsf.c
+++ b/common/tlsf.c
@@ -12,6 +12,10 @@
 
 #ifndef CONFIG_KASAN
 #define __memcpy memcpy
+/* This is only an optimization: On sandbox, with ASan, we don't have
+ * an asan-less memset implementation, so we must unpoison memory anyhow.
+ */
+#define __memzero_explicit memzero_explicit
 #endif
 
 /*
@@ -610,7 +614,7 @@ static void* block_prepare_used(control_t* control, block_header_t* block,
 
 		if (want_init_on_alloc()) {
 			kasan_unpoison_shadow(p, size);
-			memzero_explicit(p, size);
+			__memzero_explicit(p, size);
 			/*
 			 * KASAN doesn't play nicely with poisoning addresses
 			 * that are not granule-aligned, which is why we poison
@@ -1028,7 +1032,7 @@ void tlsf_free(tlsf_t tlsf, void* ptr)
 		tlsf_assert(!block_is_free(block) && "block already marked as free");
 		if (want_init_on_free()) {
 			kasan_unpoison_shadow(ptr, block_size(block));
-			memzero_explicit(ptr, block_size(block));
+			__memzero_explicit(ptr, block_size(block));
 		}
 		kasan_poison_shadow(ptr, block_size(block), 0xff);
 		block_mark_as_free(block);
-- 
2.39.5