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[34.125.181.99]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-7f4c4e9d9e3sm3079126b3a.45.2025.12.11.09.51.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 11 Dec 2025 09:51:06 -0800 (PST) Date: Thu, 11 Dec 2025 17:51:01 +0000 From: Sami Tolvanen To: Daniel Gomez Cc: Dan Carpenter , "Luck, Tony" , Chris Li , Eric Biggers , Kees Cook , Luis Chamberlain , Rusty Russell , Petr Pavlu , "linux-modules@vger.kernel.org" , Malcolm Priestley , Mauro Carvalho Chehab , Hans Verkuil , Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= , "linux-kernel@vger.kernel.org" , "linux-media@vger.kernel.org" , "linux-hardening@vger.kernel.org" Subject: Re: [PATCH 3/3] module: Add compile-time check for embedded NUL characters Message-ID: <20251211175101.GA3405942@google.com> References: <20251209001139.GA7982@quark> <20251210010020.GA2522829@google.com> <083ebd92-4b3f-47f8-bf0f-395a604b5f05@kernel.org> Precedence: bulk X-Mailing-List: linux-hardening@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <083ebd92-4b3f-47f8-bf0f-395a604b5f05@kernel.org> On Fri, Dec 12, 2025 at 02:30:48AM +0900, Daniel Gomez wrote: > > > On 12/12/2025 02.03, Sami Tolvanen wrote: > > On Thu, Dec 11, 2025 at 12:28 AM Dan Carpenter wrote: > >> > >> On Wed, Dec 10, 2025 at 02:29:45PM -0800, Luck, Tony wrote: > >>>> diff --git a/expand.c b/expand.c > >>>> index f14e7181..71221d35 100644 > >>>> --- a/expand.c > >>>> +++ b/expand.c > >>>> @@ -535,6 +535,8 @@ static int expand_compare(struct expression *expr) > >>>> expr->taint = 0; > >>>> return 0; > >>>> } > >>>> + if (left->flags & CEF_ICE && right->flags & CEF_ICE) > >>>> + expr->flags |= CEF_SET_ICE; > >>>> if (simplify_cmp_binop(expr, left->ctype)) > >>>> return 0; > >>>> if (simplify_float_cmp(expr, left->ctype)) > >> > >> I'm not an expert in the C standard, but this feels correct to me. > > > > It only fixes comparisons though, the problem still exists for other > > expressions. For example, while `_Static_assert(__builtin_strlen("") > > == 0);` works with this change, > > `_Static_assert(!__builtin_strlen(""));` still fails. Perhaps there's > > a better way to fix this than changing each expression expansion > > function to handle this flag? > > Maybe the flag fix just needs to be applied to the evaluation? Other op > structs do the same. But Dan's patch did not implement evaluate. E.g.: > > static struct symbol_op constant_p_op = { > .evaluate = evaluate_to_int_const_expr, > .expand = expand_constant_p > }; Nice catch! This seems to fix the issue for me: diff --git a/builtin.c b/builtin.c index 9149c43d..7573abf8 100644 --- a/builtin.c +++ b/builtin.c @@ -616,6 +616,7 @@ static int expand_strlen(struct expression *expr, int cost) } static struct symbol_op strlen_op = { + .evaluate = evaluate_to_int_const_expr, .expand = expand_strlen, }; I wonder if there are any other __builtin_* functions that need this too? Looks like __builtin_object_size doesn't have this either. Sami