[PATCH 5/5] x86: fortify: kmsan: fix KMSAN fortify builds

[Alexander Potapenko]

Ensure that KMSAN builds replace memset/memcpy/memmove calls with the
respective __msan_XXX functions, and that none of the macros are
redefined twice. This should allow building kernel with both
CONFIG_KMSAN and CONFIG_FORTIFY_SOURCE.

Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Nathan Chancellor <nathan@xxxxxxxxxx>
Cc: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
Reported-by: Tamas K Lengyel <tamas.lengyel@xxxxxxxxxxxx>
Link: https://github.com/google/kmsan/issues/89
Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx>
---
 arch/x86/include/asm/string_64.h | 11 +++++++----
 include/linux/fortify-string.h   | 17 +++++++++++++++--
 include/linux/kmsan_string.h     | 21 +++++++++++++++++++++
 mm/kmsan/instrumentation.c       |  1 +
 4 files changed, 44 insertions(+), 6 deletions(-)
 create mode 100644 include/linux/kmsan_string.h

diff --git a/arch/x86/include/asm/string_64.h b/arch/x86/include/asm/string_64.h
index 3b87d889b6e16..888731ccf1f67 100644
--- a/arch/x86/include/asm/string_64.h
+++ b/arch/x86/include/asm/string_64.h
@@ -10,10 +10,13 @@
 /* Even with __builtin_ the compiler may decide to use the out of line
    function. */
 
+#if defined(__SANITIZE_MEMORY__) && defined(__NO_FORTIFY)
+#include <linux/kmsan_string.h>
+#endif
+
 #define __HAVE_ARCH_MEMCPY 1
-#if defined(__SANITIZE_MEMORY__)
+#if defined(__SANITIZE_MEMORY__) && defined(__NO_FORTIFY)
 #undef memcpy
-void *__msan_memcpy(void *dst, const void *src, size_t size);
 #define memcpy __msan_memcpy
 #else
 extern void *memcpy(void *to, const void *from, size_t len);
@@ -21,7 +24,7 @@ extern void *memcpy(void *to, const void *from, size_t len);
 extern void *__memcpy(void *to, const void *from, size_t len);
 
 #define __HAVE_ARCH_MEMSET
-#if defined(__SANITIZE_MEMORY__)
+#if defined(__SANITIZE_MEMORY__) && defined(__NO_FORTIFY)
 extern void *__msan_memset(void *s, int c, size_t n);
 #undef memset
 #define memset __msan_memset
@@ -67,7 +70,7 @@ static inline void *memset64(uint64_t *s, uint64_t v, size_t n)
 }
 
 #define __HAVE_ARCH_MEMMOVE
-#if defined(__SANITIZE_MEMORY__)
+#if defined(__SANITIZE_MEMORY__) && defined(__NO_FORTIFY)
 #undef memmove
 void *__msan_memmove(void *dest, const void *src, size_t len);
 #define memmove __msan_memmove
diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h
index 4029fe368a4f6..18a31b125f9d6 100644
--- a/include/linux/fortify-string.h
+++ b/include/linux/fortify-string.h
@@ -43,11 +43,24 @@ extern __kernel_size_t __underlying_strlen(const char *p) __RENAME(strlen);
 extern char *__underlying_strncat(char *p, const char *q, __kernel_size_t count) __RENAME(strncat);
 extern char *__underlying_strncpy(char *p, const char *q, __kernel_size_t size) __RENAME(strncpy);
 #else
-#define __underlying_memchr	__builtin_memchr
-#define __underlying_memcmp	__builtin_memcmp
+
+#if defined(__SANITIZE_MEMORY__)
+/*
+ * For KMSAN builds all memcpy/memset/memmove calls should be replaced by the
+ * corresponding __msan_XXX functions.
+ */
+#include <linux/kmsan_string.h>
+#define __underlying_memcpy	__msan_memcpy
+#define __underlying_memmove	__msan_memmove
+#define __underlying_memset	__msan_memset
+#else
 #define __underlying_memcpy	__builtin_memcpy
 #define __underlying_memmove	__builtin_memmove
 #define __underlying_memset	__builtin_memset
+#endif
+
+#define __underlying_memchr	__builtin_memchr
+#define __underlying_memcmp	__builtin_memcmp
 #define __underlying_strcat	__builtin_strcat
 #define __underlying_strcpy	__builtin_strcpy
 #define __underlying_strlen	__builtin_strlen
diff --git a/include/linux/kmsan_string.h b/include/linux/kmsan_string.h
new file mode 100644
index 0000000000000..7287da6f52eff
--- /dev/null
+++ b/include/linux/kmsan_string.h
@@ -0,0 +1,21 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * KMSAN string functions API used in other headers.
+ *
+ * Copyright (C) 2022 Google LLC
+ * Author: Alexander Potapenko <glider@xxxxxxxxxx>
+ *
+ */
+#ifndef _LINUX_KMSAN_STRING_H
+#define _LINUX_KMSAN_STRING_H
+
+/*
+ * KMSAN overrides the default memcpy/memset/memmove implementations in the
+ * kernel, which requires having __msan_XXX function prototypes in several other
+ * headers. Keep them in one place instead of open-coding.
+ */
+void *__msan_memcpy(void *dst, const void *src, size_t size);
+void *__msan_memset(void *s, int c, size_t n);
+void *__msan_memmove(void *dest, const void *src, size_t len);
+
+#endif /* _LINUX_KMSAN_STRING_H */
diff --git a/mm/kmsan/instrumentation.c b/mm/kmsan/instrumentation.c
index 280d154132684..271f135f97a16 100644
--- a/mm/kmsan/instrumentation.c
+++ b/mm/kmsan/instrumentation.c
@@ -14,6 +14,7 @@
 
 #include "kmsan.h"
 #include <linux/gfp.h>
+#include <linux/kmsan_string.h>
 #include <linux/mm.h>
 #include <linux/uaccess.h>
 
-- 
2.38.0.135.g90850a2211-goog