linux-hardening - Re: [PATCH v3 7/7] kunit: Add tests for fault

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Date: Tue, 23 Apr 2024 17:22:24 +0800
From: David Gow <davidgow@...gle.com>
To: Guenter Roeck <linux@...ck-us.net>
Cc: Mickaël Salaün <mic@...ikod.net>, 
	Brendan Higgins <brendanhiggins@...gle.com>, Rae Moar <rmoar@...gle.com>, 
	Shuah Khan <skhan@...uxfoundation.org>, Alan Maguire <alan.maguire@...cle.com>, 
	Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, 
	"H . Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>, 
	James Morris <jamorris@...ux.microsoft.com>, Kees Cook <keescook@...omium.org>, 
	Luis Chamberlain <mcgrof@...nel.org>, 
	"Madhavan T . Venkataraman" <madvenka@...ux.microsoft.com>, Marco Pagani <marpagan@...hat.com>, 
	Paolo Bonzini <pbonzini@...hat.com>, Sean Christopherson <seanjc@...gle.com>, Stephen Boyd <sboyd@...nel.org>, 
	Thara Gopinath <tgopinath@...rosoft.com>, Thomas Gleixner <tglx@...utronix.de>, 
	Vitaly Kuznetsov <vkuznets@...hat.com>, Wanpeng Li <wanpengli@...cent.com>, 
	Zahra Tarkhani <ztarkhani@...rosoft.com>, kvm@...r.kernel.org, 
	linux-hardening@...r.kernel.org, linux-hyperv@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-security-module@...r.kernel.org, 
	linux-um@...ts.infradead.org, x86@...nel.org
Subject: Re: [PATCH v3 7/7] kunit: Add tests for fault

On Mon, 22 Apr 2024 at 21:36, Guenter Roeck <linux@...ck-us.net> wrote:
>
> On 4/22/24 06:08, Mickaël Salaün wrote:
> > On Fri, Apr 19, 2024 at 04:38:01PM -0700, Guenter Roeck wrote:
> >> On Fri, Apr 19, 2024 at 03:33:49PM -0700, Guenter Roeck wrote:
> >>> Hi,
> >>>
> >>> On Tue, Mar 19, 2024 at 11:48:57AM +0100, Mickaël Salaün wrote:
> >>>> Add a test case to check NULL pointer dereference and make sure it would
> >>>> result as a failed test.
> >>>>
> >>>> The full kunit_fault test suite is marked as skipped when run on UML
> >>>> because it would result to a kernel panic.
> >>>>
> >>>> Tested with:
> >>>> ./tools/testing/kunit/kunit.py run --arch x86_64 kunit_fault
> >>>> ./tools/testing/kunit/kunit.py run --arch arm64 \
> >>>>    --cross_compile=aarch64-linux-gnu- kunit_fault
> >>>>
> >>>
> >>> What is the rationale for adding those tests unconditionally whenever
> >>> CONFIG_KUNIT_TEST is enabled ? This completely messes up my test system
> >>> because it concludes that it is pointless to continue testing
> >>> after the "Unable to handle kernel NULL pointer dereference" backtrace.
> >>> At the same time, it is all or nothing, meaning I can not disable
> >>> it but still run other kunit tests.
> >>>
> >
> > CONFIG_KUNIT_TEST is to test KUnit itself.  Why does this messes up your
> > test system, and what is your test system?  Is it related to the kernel
> > warning and then the message you previously sent?
>
> It is not a warning, it is a BUG which terminates the affected kernel thread.
> NULL pointer dereferences are normally fatal, which is why I abort tests
> if one is encountered. I am not going to start introducing code into my
> scripts to ignore such warnings (or BUG messages) on a case by case basis;
> this would be unmaintainable.
>
> > https://lore.kernel.org/r/fd604ae0-5630-4745-acf2-1e51c69cf0c0@roeck-us.net
> > It seems David has a solution to suppress such warning.
> >
>
> I don't think so. My series tried to suppress warning backtraces, not BUG
> messages. BUG messages can not easily be suppressed since the reaction is
> architecture specific and typically fatal.
>
> As I said below, never mind, I just disabled CONFIG_KUNIT_TEST in my testing.
>
> Guenter
>

I think it probably makes sense to permit disabling the fault tests
independently, at least until we have a way of suppressing the
warnings.

I've sent out a patch to add a CONFIG_KUNIT_FAULT_TEST option to
disable these tests. Would that help?
https://lore.kernel.org/linux-kselftest/20240423090808.242389-1-davidgow@google.com/

(The other option is to split the tests out into a totally separate
file / module. I think that's an option (and would make the config
option more consistent with other test options) but since they're
otherwise part of the KUnit tests, I think I prefer to keep them
together.)

Cheers,
-- David

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