Commit 1a6a1dbe authored Mar 07, 2019 by Anders Roxell Committed by Linus Torvalds Mar 07, 2019

lib/ubsan: default UBSAN_ALIGNMENT to not set

When booting an allmodconfig kernel, there are a lot of false-positives.
With a message like this 'UBSAN: Undefined behaviour in...' with a call
trace that follows.

UBSAN warnings are a result of enabling noisy CONFIG_UBSAN_ALIGNMENT
which is disabled by default if HAVE_EFFICIENT_UNALIGNED_ACCESS=y.

It's noisy even if don't have efficient unaligned access, e.g.  people
often add __cacheline_aligned_in_smp in structs, but forget to align
allocations of such struct (kmalloc() give 8-byte alignment in worst
case).

Rework so that when building a allmodconfig kernel that turns everything
into '=m' or '=y' will turn off UBSAN_ALIGNMENT.

[aryabinin@virtuozzo.com: changelog addition]
Link: http://lkml.kernel.org/r/20181217150326.30933-1-anders.roxell@linaro.org


Signed-off-by: Anders Roxell <anders.roxell@linaro.org>
Suggested-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 663cb634

lib/Kconfig.ubsan

+9 −5

Original line number	Diff line number	Diff line
		@@ -27,15 +27,19 @@ config UBSAN_SANITIZE_ALL
		Enabling this option will get kernel image size increased
		significantly.

		config UBSAN_ALIGNMENT
		bool "Enable checking of pointers alignment"
		config UBSAN_NO_ALIGNMENT
		bool "Disable checking of pointers alignment"
		depends on UBSAN
		default y if !HAVE_EFFICIENT_UNALIGNED_ACCESS
		default y if HAVE_EFFICIENT_UNALIGNED_ACCESS
		help
		This option enables detection of unaligned memory accesses.
		Enabling this option on architectures that support unaligned
		This option disables the check of unaligned memory accesses.
		This option should be used when building allmodconfig.
		Disabling this option on architectures that support unaligned
		accesses may produce a lot of false positives.

		config UBSAN_ALIGNMENT
		def_bool !UBSAN_NO_ALIGNMENT

		config TEST_UBSAN
		tristate "Module for testing for undefined behavior detection"
		depends on m && UBSAN

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