tree: git://git.infradead.org/users/hch/misc.git maccess-fixups.3 head: ffc491b4d7cbc956087e89dbd171863c411f3868 commit: 5de7b23a3f5410a896ab792fd3e580d5f0e54258 [15/18] x86: use non-set_fs based maccess routines config: x86_64-randconfig-a005-20200513 (attached as .config) compiler: gcc-7 (Ubuntu 7.5.0-6ubuntu2) 7.5.0 reproduce: git checkout 5de7b23a3f5410a896ab792fd3e580d5f0e54258 # save the attached .config to linux build tree make ARCH=x86_64 If you fix the issue, kindly add following tag as appropriate Reported-by: kbuild test robot <lkp(a)intel.com&gt; All errors (new ones prefixed by >>): ld: kernel/trace/bpf_trace.o: in function `bpf_probe_read_kernel_str_common': ld: kernel/trace/bpf_trace.o: in function `bpf_strncpy': kernel/trace/bpf_trace.c:344: undefined reference to `strncpy_from_kernel_nofault' vim +252 kernel/trace/bpf_trace.c 6ae08ae3dea2cfa Daniel Borkmann 2019-11-02 232 6ae08ae3dea2cfa Daniel Borkmann 2019-11-02 233 static __always_inline int 6ae08ae3dea2cfa Daniel Borkmann 2019-11-02 234 bpf_probe_read_kernel_str_common(void *dst, u32 size, const void *unsafe_ptr, 6ae08ae3dea2cfa Daniel Borkmann 2019-11-02 235 const bool compat) 6ae08ae3dea2cfa Daniel Borkmann 2019-11-02 236 { 334a11cc65f45f1 Christoph Hellwig 2020-05-13 237 const void __user *user_ptr = (__force const void __user *)unsafe_ptr; 6ae08ae3dea2cfa Daniel Borkmann 2019-11-02 238 int ret = security_locked_down(LOCKDOWN_BPF_READ); 6ae08ae3dea2cfa Daniel Borkmann 2019-11-02 239 6ae08ae3dea2cfa Daniel Borkmann 2019-11-02 240 if (unlikely(ret < 0)) 334a11cc65f45f1 Christoph Hellwig 2020-05-13 241 goto fail; 334a11cc65f45f1 Christoph Hellwig 2020-05-13 242 6ae08ae3dea2cfa Daniel Borkmann 2019-11-02 243 /* 334a11cc65f45f1 Christoph Hellwig 2020-05-13 244 * The strncpy_from_*_nofault() calls will likely not fill the entire 6ae08ae3dea2cfa Daniel Borkmann 2019-11-02 245 * buffer, but that's okay in this circumstance as we're probing 6ae08ae3dea2cfa Daniel Borkmann 2019-11-02 246 * arbitrary memory anyway similar to bpf_probe_read_*() and might 6ae08ae3dea2cfa Daniel Borkmann 2019-11-02 247 * as well probe the stack. Thus, memory is explicitly cleared 6ae08ae3dea2cfa Daniel Borkmann 2019-11-02 248 * only in error case, so that improper users ignoring return 6ae08ae3dea2cfa Daniel Borkmann 2019-11-02 249 * code altogether don't copy garbage; otherwise length of string 6ae08ae3dea2cfa Daniel Borkmann 2019-11-02 250 * is returned that can be used for bpf_perf_event_output() et al. 6ae08ae3dea2cfa Daniel Borkmann 2019-11-02 251 */ 334a11cc65f45f1 Christoph Hellwig 2020-05-13 @252 ret = strncpy_from_kernel_nofault(dst, unsafe_ptr, size); 334a11cc65f45f1 Christoph Hellwig 2020-05-13 253 if (unlikely(ret < 0)) { 334a11cc65f45f1 Christoph Hellwig 2020-05-13 254 if (compat) 334a11cc65f45f1 Christoph Hellwig 2020-05-13 255 ret = strncpy_from_user_nofault(dst, user_ptr, size); 6ae08ae3dea2cfa Daniel Borkmann 2019-11-02 256 if (unlikely(ret < 0)) 334a11cc65f45f1 Christoph Hellwig 2020-05-13 257 goto fail; 334a11cc65f45f1 Christoph Hellwig 2020-05-13 258 } 334a11cc65f45f1 Christoph Hellwig 2020-05-13 259 return 0; 334a11cc65f45f1 Christoph Hellwig 2020-05-13 260 fail: 6ae08ae3dea2cfa Daniel Borkmann 2019-11-02 261 memset(dst, 0, size); 074f528eed408b4 Daniel Borkmann 2016-04-13 262 return ret; 2541517c32be253 Alexei Starovoitov 2015-03-25 263 } 2541517c32be253 Alexei Starovoitov 2015-03-25 264 :::::: The code at line 252 was first introduced by commit :::::: 334a11cc65f45f12f7fb8929928e68f7fb63d26d maccess: remove strncpy_from_unsafe :::::: TO: Christoph Hellwig <hch(a)lst.de&gt; :::::: CC: Christoph Hellwig <hch(a)lst.de&gt; --- 0-DAY CI Kernel Test Service, Intel Corporation https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org