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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id y8-20020a17090a16c800b00205d85cfb30sm234077pje.20.2022.10.19.10.29.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 19 Oct 2022 10:29:43 -0700 (PDT) Date: Wed, 19 Oct 2022 10:29:42 -0700 From: Kees Cook To: Alexander Potapenko Cc: Nathan Chancellor , Andrew Morton , linux-hardening@vger.kernel.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev, kasan-dev@googlegroups.com, linux-mm@kvack.org Subject: Re: -Wmacro-redefined in include/linux/fortify-string.h Message-ID: <202210190930.26BF0CE2@keescook> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 19, 2022 at 08:37:19AM -0700, Nathan Chancellor wrote: > 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? Hm, why can't KMSAN use the same thing KASAN does, and compose correctly with FORTIFY? (i.e. redefine the "__underlaying_mem*" macros?) -- Kees Cook