1*4882a593SmuzhiyunThe Undefined Behavior Sanitizer - UBSAN 2*4882a593Smuzhiyun======================================== 3*4882a593Smuzhiyun 4*4882a593SmuzhiyunUBSAN is a runtime undefined behaviour checker. 5*4882a593Smuzhiyun 6*4882a593SmuzhiyunUBSAN uses compile-time instrumentation to catch undefined behavior (UB). 7*4882a593SmuzhiyunCompiler inserts code that perform certain kinds of checks before operations 8*4882a593Smuzhiyunthat may cause UB. If check fails (i.e. UB detected) __ubsan_handle_* 9*4882a593Smuzhiyunfunction called to print error message. 10*4882a593Smuzhiyun 11*4882a593SmuzhiyunGCC has that feature since 4.9.x [1_] (see ``-fsanitize=undefined`` option and 12*4882a593Smuzhiyunits suboptions). GCC 5.x has more checkers implemented [2_]. 13*4882a593Smuzhiyun 14*4882a593SmuzhiyunReport example 15*4882a593Smuzhiyun-------------- 16*4882a593Smuzhiyun 17*4882a593Smuzhiyun:: 18*4882a593Smuzhiyun 19*4882a593Smuzhiyun ================================================================================ 20*4882a593Smuzhiyun UBSAN: Undefined behaviour in ../include/linux/bitops.h:110:33 21*4882a593Smuzhiyun shift exponent 32 is to large for 32-bit type 'unsigned int' 22*4882a593Smuzhiyun CPU: 0 PID: 0 Comm: swapper Not tainted 4.4.0-rc1+ #26 23*4882a593Smuzhiyun 0000000000000000 ffffffff82403cc8 ffffffff815e6cd6 0000000000000001 24*4882a593Smuzhiyun ffffffff82403cf8 ffffffff82403ce0 ffffffff8163a5ed 0000000000000020 25*4882a593Smuzhiyun ffffffff82403d78 ffffffff8163ac2b ffffffff815f0001 0000000000000002 26*4882a593Smuzhiyun Call Trace: 27*4882a593Smuzhiyun [<ffffffff815e6cd6>] dump_stack+0x45/0x5f 28*4882a593Smuzhiyun [<ffffffff8163a5ed>] ubsan_epilogue+0xd/0x40 29*4882a593Smuzhiyun [<ffffffff8163ac2b>] __ubsan_handle_shift_out_of_bounds+0xeb/0x130 30*4882a593Smuzhiyun [<ffffffff815f0001>] ? radix_tree_gang_lookup_slot+0x51/0x150 31*4882a593Smuzhiyun [<ffffffff8173c586>] _mix_pool_bytes+0x1e6/0x480 32*4882a593Smuzhiyun [<ffffffff83105653>] ? dmi_walk_early+0x48/0x5c 33*4882a593Smuzhiyun [<ffffffff8173c881>] add_device_randomness+0x61/0x130 34*4882a593Smuzhiyun [<ffffffff83105b35>] ? dmi_save_one_device+0xaa/0xaa 35*4882a593Smuzhiyun [<ffffffff83105653>] dmi_walk_early+0x48/0x5c 36*4882a593Smuzhiyun [<ffffffff831066ae>] dmi_scan_machine+0x278/0x4b4 37*4882a593Smuzhiyun [<ffffffff8111d58a>] ? vprintk_default+0x1a/0x20 38*4882a593Smuzhiyun [<ffffffff830ad120>] ? early_idt_handler_array+0x120/0x120 39*4882a593Smuzhiyun [<ffffffff830b2240>] setup_arch+0x405/0xc2c 40*4882a593Smuzhiyun [<ffffffff830ad120>] ? early_idt_handler_array+0x120/0x120 41*4882a593Smuzhiyun [<ffffffff830ae053>] start_kernel+0x83/0x49a 42*4882a593Smuzhiyun [<ffffffff830ad120>] ? early_idt_handler_array+0x120/0x120 43*4882a593Smuzhiyun [<ffffffff830ad386>] x86_64_start_reservations+0x2a/0x2c 44*4882a593Smuzhiyun [<ffffffff830ad4f3>] x86_64_start_kernel+0x16b/0x17a 45*4882a593Smuzhiyun ================================================================================ 46*4882a593Smuzhiyun 47*4882a593SmuzhiyunUsage 48*4882a593Smuzhiyun----- 49*4882a593Smuzhiyun 50*4882a593SmuzhiyunTo enable UBSAN configure kernel with:: 51*4882a593Smuzhiyun 52*4882a593Smuzhiyun CONFIG_UBSAN=y 53*4882a593Smuzhiyun 54*4882a593Smuzhiyunand to check the entire kernel:: 55*4882a593Smuzhiyun 56*4882a593Smuzhiyun CONFIG_UBSAN_SANITIZE_ALL=y 57*4882a593Smuzhiyun 58*4882a593SmuzhiyunTo enable instrumentation for specific files or directories, add a line 59*4882a593Smuzhiyunsimilar to the following to the respective kernel Makefile: 60*4882a593Smuzhiyun 61*4882a593Smuzhiyun- For a single file (e.g. main.o):: 62*4882a593Smuzhiyun 63*4882a593Smuzhiyun UBSAN_SANITIZE_main.o := y 64*4882a593Smuzhiyun 65*4882a593Smuzhiyun- For all files in one directory:: 66*4882a593Smuzhiyun 67*4882a593Smuzhiyun UBSAN_SANITIZE := y 68*4882a593Smuzhiyun 69*4882a593SmuzhiyunTo exclude files from being instrumented even if 70*4882a593Smuzhiyun``CONFIG_UBSAN_SANITIZE_ALL=y``, use:: 71*4882a593Smuzhiyun 72*4882a593Smuzhiyun UBSAN_SANITIZE_main.o := n 73*4882a593Smuzhiyun 74*4882a593Smuzhiyunand:: 75*4882a593Smuzhiyun 76*4882a593Smuzhiyun UBSAN_SANITIZE := n 77*4882a593Smuzhiyun 78*4882a593SmuzhiyunDetection of unaligned accesses controlled through the separate option - 79*4882a593SmuzhiyunCONFIG_UBSAN_ALIGNMENT. It's off by default on architectures that support 80*4882a593Smuzhiyununaligned accesses (CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS=y). One could 81*4882a593Smuzhiyunstill enable it in config, just note that it will produce a lot of UBSAN 82*4882a593Smuzhiyunreports. 83*4882a593Smuzhiyun 84*4882a593SmuzhiyunReferences 85*4882a593Smuzhiyun---------- 86*4882a593Smuzhiyun 87*4882a593Smuzhiyun.. _1: https://gcc.gnu.org/onlinedocs/gcc-4.9.0/gcc/Debugging-Options.html 88*4882a593Smuzhiyun.. _2: https://gcc.gnu.org/onlinedocs/gcc/Debugging-Options.html 89*4882a593Smuzhiyun.. _3: https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html 90