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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-488f5827da4sm54856085e9.14.2026.04.16.07.22.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 16 Apr 2026 07:22:37 -0700 (PDT) Date: Thu, 16 Apr 2026 15:22:35 +0100 From: David Laight To: Kees Cook Cc: linux-hardening@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH next 2/3] fortify: Optimise strnlen() Message-ID: <20260416152235.44470829@pumpkin> In-Reply-To: <202603311650.A59396A@keescook> References: <20260330132003.3379-1-david.laight.linux@gmail.com> <20260330132003.3379-3-david.laight.linux@gmail.com> <202603301650.E7C1536632@keescook> <20260331230914.43698e74@pumpkin> <202603311650.A59396A@keescook> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Tue, 31 Mar 2026 16:51:26 -0700 Kees Cook wrote: > On Tue, Mar 31, 2026 at 11:09:14PM +0100, David Laight wrote: > > Any uses should be replaced by __builtin_strlen(). > > When I looked at this before, __builtin_strlen() flip to run-time strlen > on non-constant strings, which is why I had to jump through all the > hoops to avoid calling it in those cases. > I've (finally) looked at this. - and found some extra strlen() calls. The bloat-o-meter also showed a few places that shrank - not looked at them. I'll look again, probably doing: if (__builtin_constant(str[0]) { len = __builting_strlen(str); if (__builtin_constant(len)) { /* got a constant string */ ... return ...; } } /* non-constant */ ... It only matters for a couple of functions where you don't want the actual length, trying to factor it out is probably too fragile. David