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

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Date: Mon, 22 Apr 2024 06:35:58 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: Mickaël Salaün <mic@...ikod.net>,
 David Gow <davidgow@...gle.com>
Cc: 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 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

>>
>> Oh, never mind. I just disabled CONFIG_KUNIT_TEST in my test bed
>> to "solve" the problem. I'll take that as one of those "unintended
>> consequences" items: Instead of more tests, there are fewer.
>>
>> Guenter
>>