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[195.23.151.163]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49fcd068124sm213889965e9.3.2026.09.21.03.25.42 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 21 Sep 2026 03:25:44 -0700 (PDT) Sender: Julian Braha Message-ID: Date: Mon, 21 Sep 2026 11:25:41 +0100 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/3] kconfig: Add "def_string", "def_int" and "def_hex" To: Kees Cook Cc: Nathan Chancellor , Nicolas Schier , Jonathan Corbet , Shuah Khan , Randy Dunlap , Masahiro Yamada , Arnd Bergmann , Nicolas Pitre , Krzysztof Kozlowski , Andy Shevchenko , Andrew Jones , linux-kbuild@vger.kernel.org, linux-doc@vger.kernel.org, "Lorenzo Stoakes (ARM)" , Vegard Nossum , Nauman Sabir , Tejun Heo , =?UTF-8?Q?Thomas_Wei=C3=9Fschuh?= , Matthew Maurer , Graham Roff , Miguel Ojeda , "Borislav Petkov (AMD)" , Gary Guo , linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org, conor.dooley@microchip.com References: <20260919005923.i.879-kees@kernel.org> <20260919005929.4077729-1-kees@kernel.org> <202609191431.C3BCBCD@keescook> Content-Language: en-US From: Julian Braha In-Reply-To: <202609191431.C3BCBCD@keescook> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/20/26 04:40, Kees Cook wrote: >> The second problem, is that since the order of defaults matters and >> conditions can shadow each other, def_ makes it harder for users >> to get defaults right. In the past, I've seen several config options >> with bugged defaults due to 'default' + 'def_' [2][3][4]. > > This is the one I, too, got worried about. From your example: > > config GUEST_STATE_BUFFER_TEST > - def_tristate n > + def_tristate KUNIT_ALL_TESTS > prompt "Enable Guest State Buffer unit tests" > depends on KUNIT > depends on KVM_BOOK3S_HV_POSSIBLE > - default KUNIT_ALL_TESTS > help > > Is there a way to detect this state? (I assume as a follow-up; it's a > general problem.) Unfortunately there's no way to avoid some false alarms when checking these due to macros. Example: config TUNE_CPU string depends on POWERPC64_CPU default "-mtune=power10" if $(cc-option,-mtune=power10) default "-mtune=power9" if $(cc-option,-mtune=power9) default "-mtune=power8" if $(cc-option,-mtune=power8) These macros get evaluated during preprocessing, which is ahead of when the parse tree is finished and analysis can run. Though a check for it is included in kconfirm (if merged) [1], and I've also been thinking about making this part of an optional KCONFIG_LINT setting, where some false positives could be acceptable. [1] https://lore.kernel.org/all/20260727001623.2794156-1-julianbraha@gmail.com/ - Julian Braha