Re: [PATCH] lib: Kconfig: disable dynamic sanitizers for test builds

[Hamza Mahfooz]

On 10/18/23 12:22, Marco Elver wrote:
> On Wed, 18 Oct 2023 at 17:32, 'Hamza Mahfooz' via kasan-dev
> <kasan-dev@xxxxxxxxxxxxxxxx> wrote:
> > kasan, kcsan and kmsan all have the tendency to blow up the stack
> > and there isn't a lot of value in having them enabled for test builds,
> > since they are intended to be useful for runtime debugging. So, disable
> > them for test builds.
> >
> > Signed-off-by: Hamza Mahfooz <hamza.mahfooz@xxxxxxx>
> > ---
> >   lib/Kconfig.kasan | 1 +
> >   lib/Kconfig.kcsan | 1 +
> >   lib/Kconfig.kmsan | 1 +
> >   3 files changed, 3 insertions(+)
>
> Do you have links to discussions that motivate this change? This has
> been discussed in the past. One recommendation is to adjust the

Sure, you can checkout:
https://lore.kernel.org/amd-gfx/CADnq5_OyO9CHqahFvdnx7-8s9654udgdfhUntyxfjae+iHey0Q@xxxxxxxxxxxxxx/T/#m5d227dc1ef07b1f4953312287dce4568666c5e09

> build/test scripts to exclude some combination of configs if they are
> causing issues. Or we increase CONFIG_FRAME_WARN if one of them is
> enabled (KMSAN sets it to 0, 32-bit KASAN increases it a bit).
>
> That being said, we're aware of KASAN having had more issues and there
> are some suboptions that have been disabled because of that (like
> KASAN_STACK). I'm not sure if Clang's KASAN instrumentation has had
> some recent improvements (we did investigate it, but I can't recall
> what the outcome was [1]) - maybe try a more recent compiler? However,
> KCSAN and KMSAN shouldn't have any issues (if KMSAN is enabled,

This patch was initially motivated by KCSAN (i.e. I am able to get it to
blow up the stack with a minimal .config). I don't mind dropping the
other ones since I only included them because Nathan implied that they
could cause similar issues.

> FRAME_WARN is 0). And having build tests with them enabled isn't
> useless at all: we're making sure that these tools (even though only
> for debugging), still work. We _want_ them to work during random build
> testing!
>
> Please share the concrete problem you're having, because this change
> will make things worse for everyone in the long run.
>
> [1] https://github.com/llvm/llvm-project/issues/38157
>
> > diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
> > index fdca89c05745..fbd85c4872c0 100644
> > --- a/lib/Kconfig.kasan
> > +++ b/lib/Kconfig.kasan
> > @@ -38,6 +38,7 @@ menuconfig KASAN
> >                      CC_HAS_WORKING_NOSANITIZE_ADDRESS) || \
> >                     HAVE_ARCH_KASAN_HW_TAGS
> >          depends on (SLUB && SYSFS && !SLUB_TINY) || (SLAB && !DEBUG_SLAB)
> > +       depends on !COMPILE_TEST
> >          select STACKDEPOT_ALWAYS_INIT
> >          help
> >            Enables KASAN (Kernel Address Sanitizer) - a dynamic memory safety
>
> This also disables KASAN_HW_TAGS, which is actually enabled in
> production kernels and does not use any compiler instrumentation.
>
> > diff --git a/lib/Kconfig.kcsan b/lib/Kconfig.kcsan
> > index 609ddfc73de5..7bcefdbfb46f 100644
> > --- a/lib/Kconfig.kcsan
> > +++ b/lib/Kconfig.kcsan
> > @@ -14,6 +14,7 @@ menuconfig KCSAN
> >          bool "KCSAN: dynamic data race detector"
> >          depends on HAVE_ARCH_KCSAN && HAVE_KCSAN_COMPILER
> >          depends on DEBUG_KERNEL && !KASAN
> > +       depends on !COMPILE_TEST
> >          select CONSTRUCTORS
> >          select STACKTRACE
> >          help
> > diff --git a/lib/Kconfig.kmsan b/lib/Kconfig.kmsan
> > index ef2c8f256c57..eb05c885d3fd 100644
> > --- a/lib/Kconfig.kmsan
> > +++ b/lib/Kconfig.kmsan
> > @@ -13,6 +13,7 @@ config KMSAN
> >          depends on HAVE_ARCH_KMSAN && HAVE_KMSAN_COMPILER
> >          depends on SLUB && DEBUG_KERNEL && !KASAN && !KCSAN
> >          depends on !PREEMPT_RT
> > +       depends on !COMPILE_TEST
>
> KMSAN already selects FRAME_WARN of 0 and should not cause you any
> issues during build testing.
>
> Nack.
--
Hamza