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lib/ubsan: default UBSAN_ALIGNMENT to not set

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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.

[[email protected]: changelog addition]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Anders Roxell <[email protected]>
Suggested-by: Arnd Bergmann <[email protected]>
Acked-by: Andrey Ryabinin <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Anders Roxell authored and Linus Torvalds committed 2019-03-07 18:32:02 -08:00
1 parent 663cb6340c
commit 1a6a1dbeb7
1 file changed
+9 -5
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lib/Kconfig.ubsan
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@@ -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