linux-kernel - -Wmacro-redefined in include/linux/fortify-string.h

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Date:   Wed, 19 Oct 2022 08:37:19 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Kees Cook <keescook@...omium.org>,
        Alexander Potapenko <glider@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev, kasan-dev@...glegroups.com,
        linux-mm@...ck.org
Subject: -Wmacro-redefined in include/linux/fortify-string.h

Hi all,

I am seeing the following set of warnings when building an x86_64
configuration that has CONFIG_FORTIFY_SOURCE=y and CONFIG_KMSAN=y:

  In file included from scripts/mod/devicetable-offsets.c:3:
  In file included from ./include/linux/mod_devicetable.h:13:
  In file included from ./include/linux/uuid.h:12:
  In file included from ./include/linux/string.h:253:
  ./include/linux/fortify-string.h:496:9: error: 'memcpy' macro redefined [-Werror,-Wmacro-redefined]
  #define memcpy(p, q, s)  __fortify_memcpy_chk(p, q, s,                  \
          ^
  ./arch/x86/include/asm/string_64.h:17:9: note: previous definition is here
  #define memcpy __msan_memcpy
          ^
  In file included from scripts/mod/devicetable-offsets.c:3:
  In file included from ./include/linux/mod_devicetable.h:13:
  In file included from ./include/linux/uuid.h:12:
  In file included from ./include/linux/string.h:253:
  ./include/linux/fortify-string.h:500:9: error: 'memmove' macro redefined [-Werror,-Wmacro-redefined]
  #define memmove(p, q, s)  __fortify_memcpy_chk(p, q, s,                 \
          ^
  ./arch/x86/include/asm/string_64.h:73:9: note: previous definition is here
  #define memmove __msan_memmove
          ^
  2 errors generated.

I can see that commit ff901d80fff6 ("x86: kmsan: use __msan_ string
functions where possible.") appears to include a fix up for this warning
with memset() but not memcpy() or memmove(). If I apply a similar fix up
like so:

diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h
index 4029fe368a4f..718ee17b31e3 100644
--- a/include/linux/fortify-string.h
+++ b/include/linux/fortify-string.h
@@ -493,6 +493,7 @@ __FORTIFY_INLINE bool fortify_memcpy_chk(__kernel_size_t size,
  * __struct_size() vs __member_size() must be captured here to avoid
  * evaluating argument side-effects further into the macro layers.
  */
+#ifndef CONFIG_KMSAN
 #define memcpy(p, q, s)  __fortify_memcpy_chk(p, q, s,			\
 		__struct_size(p), __struct_size(q),			\
 		__member_size(p), __member_size(q),			\
@@ -501,6 +502,7 @@ __FORTIFY_INLINE bool fortify_memcpy_chk(__kernel_size_t size,
 		__struct_size(p), __struct_size(q),			\
 		__member_size(p), __member_size(q),			\
 		memmove)
+#endif
 
 extern void *__real_memscan(void *, int, __kernel_size_t) __RENAME(memscan);
 __FORTIFY_INLINE void *memscan(void * const POS0 p, int c, __kernel_size_t size)

Then the instances of -Wmacro-redefined disappear but the fortify tests
no longer pass for somewhat obvious reasons:

  warning: unsafe memcpy() usage lacked '__read_overflow2' symbol in lib/test_fortify/read_overflow2-memcpy.c
  warning: unsafe memmove() usage lacked '__read_overflow2' symbol in lib/test_fortify/read_overflow2-memmove.c
  warning: unsafe memcpy() usage lacked '__read_overflow2_field' symbol in lib/test_fortify/read_overflow2_field-memcpy.c
  warning: unsafe memmove() usage lacked '__read_overflow2_field' symbol in lib/test_fortify/read_overflow2_field-memmove.c
  warning: unsafe memcpy() usage lacked '__write_overflow' symbol in lib/test_fortify/write_overflow-memcpy.c
  warning: unsafe memmove() usage lacked '__write_overflow' symbol in lib/test_fortify/write_overflow-memmove.c
  warning: unsafe memset() usage lacked '__write_overflow' symbol in lib/test_fortify/write_overflow-memset.c
  warning: unsafe memcpy() usage lacked '__write_overflow_field' symbol in lib/test_fortify/write_overflow_field-memcpy.c
  warning: unsafe memmove() usage lacked '__write_overflow_field' symbol in lib/test_fortify/write_overflow_field-memmove.c
  warning: unsafe memset() usage lacked '__write_overflow_field' symbol in lib/test_fortify/write_overflow_field-memset.c

Should CONFIG_KMSAN depend on CONFIG_FORTIFY_SOURCE=n like so? It seems
like the two features are incompatible if I am reading ff901d80fff6
correctly.

diff --git a/lib/Kconfig.kmsan b/lib/Kconfig.kmsan
index b2489dd6503f..6a681621e3c5 100644
--- a/lib/Kconfig.kmsan
+++ b/lib/Kconfig.kmsan
@@ -11,7 +11,7 @@ config HAVE_KMSAN_COMPILER
 config KMSAN
 	bool "KMSAN: detector of uninitialized values use"
 	depends on HAVE_ARCH_KMSAN && HAVE_KMSAN_COMPILER
-	depends on SLUB && DEBUG_KERNEL && !KASAN && !KCSAN
+	depends on SLUB && DEBUG_KERNEL && !KASAN && !KCSAN && !FORTIFY_SOURCE
 	select STACKDEPOT
 	select STACKDEPOT_ALWAYS_INIT
 	help

or is there a different obvious fix that I am missing?

Cheers,
Nathan