Blame - Documentation/dev-tools/ubsan.rst - kernel/msm-4.19

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Jonathan Corbet	1ead009	2016-08-07 15:35:42 -0600	[diff] [blame]	1	The Undefined Behavior Sanitizer - UBSAN
				2	========================================
Andrey Ryabinin	c6d3085	2016-01-20 15:00:55 -0800	[diff] [blame]	3
				4	UBSAN is a runtime undefined behaviour checker.
				5
				6	UBSAN uses compile-time instrumentation to catch undefined behavior (UB).
				7	Compiler inserts code that perform certain kinds of checks before operations
				8	that may cause UB. If check fails (i.e. UB detected) __ubsan_handle_*
				9	function called to print error message.
				10
Jonathan Corbet	1ead009	2016-08-07 15:35:42 -0600	[diff] [blame]	11	GCC has that feature since 4.9.x [1_] (see ``-fsanitize=undefined`` option and
				12	its suboptions). GCC 5.x has more checkers implemented [2_].
Andrey Ryabinin	c6d3085	2016-01-20 15:00:55 -0800	[diff] [blame]	13
				14	Report example
Jonathan Corbet	1ead009	2016-08-07 15:35:42 -0600	[diff] [blame]	15	--------------
				16
				17	::
Andrey Ryabinin	c6d3085	2016-01-20 15:00:55 -0800	[diff] [blame]	18
				19	================================================================================
				20	UBSAN: Undefined behaviour in ../include/linux/bitops.h:110:33
				21	shift exponent 32 is to large for 32-bit type 'unsigned int'
				22	CPU: 0 PID: 0 Comm: swapper Not tainted 4.4.0-rc1+ #26
				23	0000000000000000 ffffffff82403cc8 ffffffff815e6cd6 0000000000000001
				24	ffffffff82403cf8 ffffffff82403ce0 ffffffff8163a5ed 0000000000000020
				25	ffffffff82403d78 ffffffff8163ac2b ffffffff815f0001 0000000000000002
				26	Call Trace:
				27	[<ffffffff815e6cd6>] dump_stack+0x45/0x5f
				28	[<ffffffff8163a5ed>] ubsan_epilogue+0xd/0x40
				29	[<ffffffff8163ac2b>] __ubsan_handle_shift_out_of_bounds+0xeb/0x130
				30	[<ffffffff815f0001>] ? radix_tree_gang_lookup_slot+0x51/0x150
				31	[<ffffffff8173c586>] _mix_pool_bytes+0x1e6/0x480
				32	[<ffffffff83105653>] ? dmi_walk_early+0x48/0x5c
				33	[<ffffffff8173c881>] add_device_randomness+0x61/0x130
				34	[<ffffffff83105b35>] ? dmi_save_one_device+0xaa/0xaa
				35	[<ffffffff83105653>] dmi_walk_early+0x48/0x5c
				36	[<ffffffff831066ae>] dmi_scan_machine+0x278/0x4b4
				37	[<ffffffff8111d58a>] ? vprintk_default+0x1a/0x20
				38	[<ffffffff830ad120>] ? early_idt_handler_array+0x120/0x120
				39	[<ffffffff830b2240>] setup_arch+0x405/0xc2c
				40	[<ffffffff830ad120>] ? early_idt_handler_array+0x120/0x120
				41	[<ffffffff830ae053>] start_kernel+0x83/0x49a
				42	[<ffffffff830ad120>] ? early_idt_handler_array+0x120/0x120
				43	[<ffffffff830ad386>] x86_64_start_reservations+0x2a/0x2c
				44	[<ffffffff830ad4f3>] x86_64_start_kernel+0x16b/0x17a
				45	================================================================================
				46
				47	Usage
				48	-----
				49
Jonathan Corbet	1ead009	2016-08-07 15:35:42 -0600	[diff] [blame]	50	To enable UBSAN configure kernel with::
Andrey Ryabinin	c6d3085	2016-01-20 15:00:55 -0800	[diff] [blame]	51
				52	CONFIG_UBSAN=y
				53
Jonathan Corbet	1ead009	2016-08-07 15:35:42 -0600	[diff] [blame]	54	and to check the entire kernel::
Andrey Ryabinin	c6d3085	2016-01-20 15:00:55 -0800	[diff] [blame]	55
				56	CONFIG_UBSAN_SANITIZE_ALL=y
				57
				58	To enable instrumentation for specific files or directories, add a line
				59	similar to the following to the respective kernel Makefile:
				60
Jonathan Corbet	1ead009	2016-08-07 15:35:42 -0600	[diff] [blame]	61	- For a single file (e.g. main.o)::
Andrey Ryabinin	c6d3085	2016-01-20 15:00:55 -0800	[diff] [blame]	62
Jonathan Corbet	1ead009	2016-08-07 15:35:42 -0600	[diff] [blame]	63	UBSAN_SANITIZE_main.o := y
				64
				65	- For all files in one directory::
				66
				67	UBSAN_SANITIZE := y
Andrey Ryabinin	c6d3085	2016-01-20 15:00:55 -0800	[diff] [blame]	68
				69	To exclude files from being instrumented even if
Jonathan Corbet	1ead009	2016-08-07 15:35:42 -0600	[diff] [blame]	70	``CONFIG_UBSAN_SANITIZE_ALL=y``, use::
Andrey Ryabinin	c6d3085	2016-01-20 15:00:55 -0800	[diff] [blame]	71
Jonathan Corbet	1ead009	2016-08-07 15:35:42 -0600	[diff] [blame]	72	UBSAN_SANITIZE_main.o := n
				73
				74	and::
				75
				76	UBSAN_SANITIZE := n
Andrey Ryabinin	c6d3085	2016-01-20 15:00:55 -0800	[diff] [blame]	77
				78	Detection of unaligned accesses controlled through the separate option -
				79	CONFIG_UBSAN_ALIGNMENT. It's off by default on architectures that support
				80	unaligned accesses (CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS=y). One could
				81	still enable it in config, just note that it will produce a lot of UBSAN
				82	reports.
				83
				84	References
				85	----------
				86
Jonathan Corbet	1ead009	2016-08-07 15:35:42 -0600	[diff] [blame]	87	.. _1: https://gcc.gnu.org/onlinedocs/gcc-4.9.0/gcc/Debugging-Options.html
				88	.. _2: https://gcc.gnu.org/onlinedocs/gcc/Debugging-Options.html