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[209.85.208.48]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-6152a0e65a2sm221840a12.42.2025.07.26.16.37.50 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 26 Jul 2025 16:37:50 -0700 (PDT) Received: by mail-ed1-f48.google.com with SMTP id 4fb4d7f45d1cf-60c60f7eeaaso5286892a12.0 for ; Sat, 26 Jul 2025 16:37:50 -0700 (PDT) X-Forwarded-Encrypted: i=1; AJvYcCURHDGv1NOC0LicELZsp63vtPFBIIxifbw3GXYhWJlyQJCKBorcgQizuViSe8ml8bQ6lvHxdGscHw==@kvack.org X-Received: by 2002:a05:6402:483:b0:611:f4b2:379c with SMTP id 4fb4d7f45d1cf-614f1dced8amr5514831a12.20.1753573070075; Sat, 26 Jul 2025 16:37:50 -0700 (PDT) MIME-Version: 1.0 References: <20250724123612.206110-1-bhupesh@igalia.com> <20250724123612.206110-3-bhupesh@igalia.com> <202507241640.572BF86C70@keescook> In-Reply-To: From: Linus Torvalds Date: Sat, 26 Jul 2025 16:37:33 -0700 X-Gmail-Original-Message-ID: X-Gm-Features: Ac12FXwLhT2VoOEv9kNeOdgouvN4zZ9YLvHzVMPIsLMuRmQFnkSkLFn13r5tjO0 Message-ID: Subject: Re: [PATCH v6 2/3] treewide: Switch memcpy() users of 'task->comm' to a more safer implementation To: Kees Cook Cc: Bhupesh , akpm@linux-foundation.org, kernel-dev@igalia.com, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, linux-perf-users@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, oliver.sang@intel.com, lkp@intel.com, laoar.shao@gmail.com, pmladek@suse.com, rostedt@goodmis.org, mathieu.desnoyers@efficios.com, arnaldo.melo@gmail.com, alexei.starovoitov@gmail.com, andrii.nakryiko@gmail.com, mirq-linux@rere.qmqm.pl, peterz@infradead.org, willy@infradead.org, david@redhat.com, viro@zeniv.linux.org.uk, ebiederm@xmission.com, brauner@kernel.org, jack@suse.cz, mingo@redhat.com, juri.lelli@redhat.com, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, linux-trace-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: 5BAE940009 X-Rspam-User: X-Rspamd-Server: rspam09 X-Stat-Signature: pp8yr5ah8b64o8qfwg4qbqzystpaz8ao X-HE-Tag: 1753573073-328276 X-HE-Meta: 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 IgjqdyA5 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sat, 26 Jul 2025 at 16:19, Kees Cook wrote: > > That works for me! I just get twitchy around seeing memcpy used for strings. :) if we're gonna NUL after the memcpy, just use strscpy_pad(). I do worry a tiny bit about performance. Because 'memcpy+set last byte to NUL' really is just a couple of instructions when we're talking small constant-sized arrays. strscpy_pad() isn't horrible, but it's still at another level. And most of the cost is that "return the length" which people often don't care about. Dang, I wish we had some compiler trick to say "if the value isn't used, do X, if it _is_ used do Y". It's such a trivial thing in the compiler itself, and the information is there, but I don't think it is exposed in any useful way. In fact, it *is* exposed in one way I can think of: __attribute__((__warn_unused_result__)) but not in a useful form for actually generating different code. Some kind of "__builtin_if_used(x,y)" where it picks 'x' if the value is used, and 'y' if it isn't would be lovely for this. Then you could do things like #define my_helper(x) \ __builtin_if_used( \ full_semantics(x), \ simpler_version(x)) when having a return value means extra work and most people don't care. Maybe it exists in some form that I haven't thought of? Any compiler people around? Linus