The Undefined Behavior Sanitizer - UBSAN
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========================================
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UBSAN is a runtime undefined behaviour checker.
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UBSAN uses compile-time instrumentation to catch undefined behavior (UB).
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Compiler inserts code that perform certain kinds of checks before operations
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that may cause UB. If check fails (i.e. UB detected) __ubsan_handle_*
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function called to print error message.
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GCC has that feature since 4.9.x [1_] (see ``-fsanitize=undefined`` option and
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its suboptions). GCC 5.x has more checkers implemented [2_].
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Report example
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--------------
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::
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================================================================================
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UBSAN: Undefined behaviour in ../include/linux/bitops.h:110:33
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shift exponent 32 is to large for 32-bit type 'unsigned int'
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CPU: 0 PID: 0 Comm: swapper Not tainted 4.4.0-rc1+ #26
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0000000000000000 ffffffff82403cc8 ffffffff815e6cd6 0000000000000001
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ffffffff82403cf8 ffffffff82403ce0 ffffffff8163a5ed 0000000000000020
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ffffffff82403d78 ffffffff8163ac2b ffffffff815f0001 0000000000000002
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Call Trace:
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[<ffffffff815e6cd6>] dump_stack+0x45/0x5f
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[<ffffffff8163a5ed>] ubsan_epilogue+0xd/0x40
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[<ffffffff8163ac2b>] __ubsan_handle_shift_out_of_bounds+0xeb/0x130
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[<ffffffff815f0001>] ? radix_tree_gang_lookup_slot+0x51/0x150
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[<ffffffff8173c586>] _mix_pool_bytes+0x1e6/0x480
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[<ffffffff83105653>] ? dmi_walk_early+0x48/0x5c
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[<ffffffff8173c881>] add_device_randomness+0x61/0x130
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[<ffffffff83105b35>] ? dmi_save_one_device+0xaa/0xaa
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[<ffffffff83105653>] dmi_walk_early+0x48/0x5c
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[<ffffffff831066ae>] dmi_scan_machine+0x278/0x4b4
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[<ffffffff8111d58a>] ? vprintk_default+0x1a/0x20
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[<ffffffff830ad120>] ? early_idt_handler_array+0x120/0x120
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[<ffffffff830b2240>] setup_arch+0x405/0xc2c
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[<ffffffff830ad120>] ? early_idt_handler_array+0x120/0x120
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[<ffffffff830ae053>] start_kernel+0x83/0x49a
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[<ffffffff830ad120>] ? early_idt_handler_array+0x120/0x120
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[<ffffffff830ad386>] x86_64_start_reservations+0x2a/0x2c
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[<ffffffff830ad4f3>] x86_64_start_kernel+0x16b/0x17a
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================================================================================
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Usage
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-----
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To enable UBSAN configure kernel with::
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CONFIG_UBSAN=y
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and to check the entire kernel::
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CONFIG_UBSAN_SANITIZE_ALL=y
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To enable instrumentation for specific files or directories, add a line
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similar to the following to the respective kernel Makefile:
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- For a single file (e.g. main.o)::
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UBSAN_SANITIZE_main.o := y
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- For all files in one directory::
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UBSAN_SANITIZE := y
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To exclude files from being instrumented even if
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``CONFIG_UBSAN_SANITIZE_ALL=y``, use::
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UBSAN_SANITIZE_main.o := n
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and::
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UBSAN_SANITIZE := n
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Detection of unaligned accesses controlled through the separate option -
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CONFIG_UBSAN_ALIGNMENT. It's off by default on architectures that support
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unaligned accesses (CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS=y). One could
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still enable it in config, just note that it will produce a lot of UBSAN
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reports.
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References
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----------
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.. _1: https://gcc.gnu.org/onlinedocs/gcc-4.9.0/gcc/Debugging-Options.html
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.. _2: https://gcc.gnu.org/onlinedocs/gcc/Debugging-Options.html
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.. _3: https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html
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