| Message ID | 20181217150326.30933-1-anders.roxell@linaro.org |
|---|---|
| State | Accepted |
| Commit | 1a6a1dbeb72fce7517665b365085ea405490c2d5 |
| Headers | show |
| Series | lib/ubsan: default UBSAN_ALIGNMENT to not set | expand |
On 12/17/18 6:03 PM, Anders Roxell wrote: > 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. > > Reworked so that when building a allmodconfig kernel that turns > everything into '=m' or '=y' will turn off UBSAN_ALIGNMENT. > > Suggested-by: Arnd Bergmann <arnd@arndb.de> > Signed-off-by: Anders Roxell <anders.roxell@linaro.org> > --- Acked-by: Andrey Ryabinin <aryabinin@virtuozzo.com> > lib/Kconfig.ubsan | 14 +++++++++----- > 1 file changed, 9 insertions(+), 5 deletions(-) > > diff --git a/lib/Kconfig.ubsan b/lib/Kconfig.ubsan > index 98fa559ebd80..a2ae4a8e4fa6 100644 > --- a/lib/Kconfig.ubsan > +++ b/lib/Kconfig.ubsan > @@ -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 >
On Fri, 11 Jan 2019 22:01:16 +0300 Andrey Ryabinin <aryabinin@virtuozzo.com> wrote: > > > On 12/17/18 6:03 PM, Anders Roxell wrote: > > 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. > > > > Reworked so that when building a allmodconfig kernel that turns > > everything into '=m' or '=y' will turn off UBSAN_ALIGNMENT. > > > > Suggested-by: Arnd Bergmann <arnd@arndb.de> > > Signed-off-by: Anders Roxell <anders.roxell@linaro.org> > > --- > > Acked-by: Andrey Ryabinin <aryabinin@virtuozzo.com> > Confused. Why does allmodconfig result in UBSAN warnings?
On 1/30/19 4:36 AM, Andrew Morton wrote: > On Fri, 11 Jan 2019 22:01:16 +0300 Andrey Ryabinin <aryabinin@virtuozzo.com> wrote: > >> >> >> On 12/17/18 6:03 PM, Anders Roxell wrote: >>> 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. >>> >>> Reworked so that when building a allmodconfig kernel that turns >>> everything into '=m' or '=y' will turn off UBSAN_ALIGNMENT. >>> >>> Suggested-by: Arnd Bergmann <arnd@arndb.de> >>> Signed-off-by: Anders Roxell <anders.roxell@linaro.org> >>> --- >> >> Acked-by: Andrey Ryabinin <aryabinin@virtuozzo.com> >> > > Confused. Why does allmodconfig result in UBSAN warnings? > UBSAN warnings is 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).
On Wed, Jan 30, 2019 at 6:12 PM Andrey Ryabinin <aryabinin@virtuozzo.com> wrote: > On 1/30/19 4:36 AM, Andrew Morton wrote: > > On Fri, 11 Jan 2019 22:01:16 +0300 Andrey Ryabinin <aryabinin@virtuozzo.com> wrote: > >> On 12/17/18 6:03 PM, Anders Roxell wrote: > >>> 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. > >>> > >>> Reworked so that when building a allmodconfig kernel that turns > >>> everything into '=m' or '=y' will turn off UBSAN_ALIGNMENT. > >>> > >>> Suggested-by: Arnd Bergmann <arnd@arndb.de> > >>> Signed-off-by: Anders Roxell <anders.roxell@linaro.org> > >>> --- > >> > >> Acked-by: Andrey Ryabinin <aryabinin@virtuozzo.com> > >> > > > > Confused. Why does allmodconfig result in UBSAN warnings? > > > > UBSAN warnings is 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). That would be a fixable issue, but there is another one that I looked at with Anders: We have a number of list_for_each_entry_safe() loops that use a list_head on the stack and add objects of a type with large alignment. When list_for_each_entry_safe() gets to the end of that list, it sees a pointer to an unaligned structure starting few bytes before the list_head on stack. The only element of that structure that is ever used is that list_head, so there is no actual problem, but the warning triggers nonetheless. Arnd
diff --git a/lib/Kconfig.ubsan b/lib/Kconfig.ubsan index 98fa559ebd80..a2ae4a8e4fa6 100644 --- a/lib/Kconfig.ubsan +++ b/lib/Kconfig.ubsan @@ -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
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. Reworked so that when building a allmodconfig kernel that turns everything into '=m' or '=y' will turn off UBSAN_ALIGNMENT. Suggested-by: Arnd Bergmann <arnd@arndb.de> Signed-off-by: Anders Roxell <anders.roxell@linaro.org> --- lib/Kconfig.ubsan | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-) -- 2.19.2