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Date: Fri, 11 Feb 2022 16:35:41 -0800 From: Jakub Kicinski <kuba@...nel.org> To: Marc Kleine-Budde <mkl@...gutronix.de>, Kees Cook <keescook@...omium.org> Cc: Eric Dumazet <edumazet@...gle.com>, netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net> Subject: Re: ether_addr_equal_64bits breakage with gcc-12 On Fri, 11 Feb 2022 15:12:13 +0100 Marc Kleine-Budde wrote: > Hello, > > the current arm-linux-gnueabihf-gcc 12 snapshot in Debian breaks (at > least with CONFIG_WERROR=y): > > | CC net/core/dev.o > | net/core/dev.c: In function ‘bpf_prog_run_generic_xdp’: > | net/core/dev.c:4618:21: warning: ‘ether_addr_equal_64bits’ reading 8 bytes from a region of size 6 [-Wstringop-overread] > | 4618 | orig_host = ether_addr_equal_64bits(eth->h_dest, skb->dev->dev_addr); > | | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > | net/core/dev.c:4618:21: note: referencing argument 1 of type ‘const u8[8]’ {aka ‘const unsigned char[8]’} > | net/core/dev.c:4618:21: note: referencing argument 2 of type ‘const u8[8]’ {aka ‘const unsigned char[8]’} > | In file included from net/core/dev.c:91: > | include/linux/etherdevice.h:375:20: note: in a call to function ‘ether_addr_equal_64bits’ > | 375 | static inline bool ether_addr_equal_64bits(const u8 addr1[6+2], > | | ^~~~~~~~~~~~~~~~~~~~~~~ > | net/core/dev.c:4619:22: warning: ‘is_multicast_ether_addr_64bits’ reading 8 bytes from a region of size 6 [-Wstringop-overread] > | 4619 | orig_bcast = is_multicast_ether_addr_64bits(eth->h_dest); > | | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > | net/core/dev.c:4619:22: note: referencing argument 1 of type ‘const u8[8]’ {aka ‘const unsigned char[8]’} > | include/linux/etherdevice.h:137:20: note: in a call to function ‘is_multicast_ether_addr_64bits’ > | 137 | static inline bool is_multicast_ether_addr_64bits(const u8 addr[6+2]) > | | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > | net/core/dev.c:4646:27: warning: ‘ether_addr_equal_64bits’ reading 8 bytes from a region of size 6 [-Wstringop-overread] > | 4646 | (orig_host != ether_addr_equal_64bits(eth->h_dest, > | | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > | 4647 | skb->dev->dev_addr)) || > | | ~~~~~~~~~~~~~~~~~~~ > | net/core/dev.c:4646:27: note: referencing argument 1 of type ‘const u8[8]’ {aka ‘const unsigned char[8]’} > | net/core/dev.c:4646:27: note: referencing argument 2 of type ‘const u8[8]’ {aka ‘const unsigned char[8]’} > | include/linux/etherdevice.h:375:20: note: in a call to function ‘ether_addr_equal_64bits’ > | 375 | static inline bool ether_addr_equal_64bits(const u8 addr1[6+2], > | | ^~~~~~~~~~~~~~~~~~~~~~~ > | net/core/dev.c:4648:28: warning: ‘is_multicast_ether_addr_64bits’ reading 8 bytes from a region of size 6 [-Wstringop-overread] > | 4648 | (orig_bcast != is_multicast_ether_addr_64bits(eth->h_dest))) { > | | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > | net/core/dev.c:4648:28: note: referencing argument 1 of type ‘const u8[8]’ {aka ‘const unsigned char[8]’} > | include/linux/etherdevice.h:137:20: note: in a call to function ‘is_multicast_ether_addr_64bits’ > | 137 | static inline bool is_multicast_ether_addr_64bits(const u8 addr[6+2]) > | | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > | arm-linux-gnueabihf-gcc -v > | Using built-in specs. > | COLLECT_GCC=/usr/bin/arm-linux-gnueabihf-gcc > | COLLECT_LTO_WRAPPER=/usr/lib/gcc-cross/arm-linux-gnueabihf/12/lto-wrapper > | Target: arm-linux-gnueabihf > | Configured with: ../src/configure -v --with-pkgversion='Debian 12-20220126-1' --with-bugurl=file:///usr/share/doc/gcc-12/README.Bugs --enable-languages=c,ada,c++,go,d,fortran,objc,obj-c++,m2 --prefix=/usr --with-gcc-major-version-only --program-suffix=-12 --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new --enable-gnu-unique-object --disable-libitm --disable-libquadmath --disable-libquadmath-support --enable-plugin --enable-default-pie --with-system-zlib --enable-libphobos-checking=release --without-target-system-zlib --enable-multiarch --disable-sjlj-exceptions --with-arch=armv7-a+fp --with-float=hard --with-mode=thumb --disable-werror --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=arm-linux-gnueabihf --program-prefix=arm-linux-gnueabihf- --includedir=/usr/arm-linux-gnueabihf/include > | Thread model: posix > | Supported LTO compression algorithms: zlib zstd > | gcc version 12.0.1 20220126 (experimental) [master r12-6872-gf3e6ef7d873] (Debian 12-20220126-1) Maybe Kees will have as suggestion - Kees, are there any best practices for dealing with such issues? For the reference we do a oversized load from a structure (read 8B of a 6B array): struct ethhdr { unsigned char h_dest[6]; unsigned char h_source[6]; __be16 h_proto; } __attribute__((packed)); But then discard the irrelevant bytes: #if defined(CONFIG_HAVE_EFFICIENT... u64 fold = (*(const u64 *)addr1) ^ (*(const u64 *)addr2); #ifdef __BIG_ENDIAN return (fold >> 16) == 0; #else ... The structure is uAPI, for added fun.
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