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1.. SPDX-License-Identifier: GPL-2.02 3Undefined Behavior Sanitizer - UBSAN4====================================5 6UBSAN is a runtime undefined behaviour checker.7 8UBSAN uses compile-time instrumentation to catch undefined behavior (UB).9Compiler inserts code that perform certain kinds of checks before operations10that may cause UB. If check fails (i.e. UB detected) __ubsan_handle_*11function called to print error message.12 13GCC has that feature since 4.9.x [1_] (see ``-fsanitize=undefined`` option and14its suboptions). GCC 5.x has more checkers implemented [2_].15 16Report example17--------------18 19::20 21 ================================================================================22 UBSAN: Undefined behaviour in ../include/linux/bitops.h:110:3323 shift exponent 32 is to large for 32-bit type 'unsigned int'24 CPU: 0 PID: 0 Comm: swapper Not tainted 4.4.0-rc1+ #2625 0000000000000000 ffffffff82403cc8 ffffffff815e6cd6 000000000000000126 ffffffff82403cf8 ffffffff82403ce0 ffffffff8163a5ed 000000000000002027 ffffffff82403d78 ffffffff8163ac2b ffffffff815f0001 000000000000000228 Call Trace:29 [<ffffffff815e6cd6>] dump_stack+0x45/0x5f30 [<ffffffff8163a5ed>] ubsan_epilogue+0xd/0x4031 [<ffffffff8163ac2b>] __ubsan_handle_shift_out_of_bounds+0xeb/0x13032 [<ffffffff815f0001>] ? radix_tree_gang_lookup_slot+0x51/0x15033 [<ffffffff8173c586>] _mix_pool_bytes+0x1e6/0x48034 [<ffffffff83105653>] ? dmi_walk_early+0x48/0x5c35 [<ffffffff8173c881>] add_device_randomness+0x61/0x13036 [<ffffffff83105b35>] ? dmi_save_one_device+0xaa/0xaa37 [<ffffffff83105653>] dmi_walk_early+0x48/0x5c38 [<ffffffff831066ae>] dmi_scan_machine+0x278/0x4b439 [<ffffffff8111d58a>] ? vprintk_default+0x1a/0x2040 [<ffffffff830ad120>] ? early_idt_handler_array+0x120/0x12041 [<ffffffff830b2240>] setup_arch+0x405/0xc2c42 [<ffffffff830ad120>] ? early_idt_handler_array+0x120/0x12043 [<ffffffff830ae053>] start_kernel+0x83/0x49a44 [<ffffffff830ad120>] ? early_idt_handler_array+0x120/0x12045 [<ffffffff830ad386>] x86_64_start_reservations+0x2a/0x2c46 [<ffffffff830ad4f3>] x86_64_start_kernel+0x16b/0x17a47 ================================================================================48 49Usage50-----51 52To enable UBSAN, configure the kernel with::53 54 CONFIG_UBSAN=y55 56To exclude files from being instrumented use::57 58 UBSAN_SANITIZE_main.o := n59 60and to exclude all targets in one directory use::61 62 UBSAN_SANITIZE := n63 64When disabled for all targets, specific files can be enabled using::65 66 UBSAN_SANITIZE_main.o := y67 68Detection of unaligned accesses controlled through the separate option -69CONFIG_UBSAN_ALIGNMENT. It's off by default on architectures that support70unaligned accesses (CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS=y). One could71still enable it in config, just note that it will produce a lot of UBSAN72reports.73 74References75----------76 77.. _1: https://gcc.gnu.org/onlinedocs/gcc-4.9.0/gcc/Debugging-Options.html78.. _2: https://gcc.gnu.org/onlinedocs/gcc/Debugging-Options.html79.. _3: https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html80