From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 2CB3DD5C0DA for ; Tue, 16 Dec 2025 08:27:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=18QUzibWbUvzdO3mSa7PVgq3DCScRHDw8cH0GYL+t4Q=; b=gG6ZdmeFWpr2V29rbJ76orkdpo Pj2PVPud08gTckui94r6WZxL9f/LFJbvGtEeJ0qrO80Z8uGTnB1CWT8rrv3eVGOwVhTvZf89mevZJ koY0yRq4L2RKrEckMZ6znkhpYOq2XdBNKslzVJQMXSaklsx4mlbbi2eSWBx7AdQT9XujbZUOC9poY OXNNzbiK+jwE0H57FVpWfNq9E78hEzQwRPe84KscSTspb5qOSc2FkZ36fWPTMh5dWLt8Z7oJ7TfeO TfOudeeFsahGOa9Y4iAyQO36rWSD3jQTX5Y+6gR4y8Ty02dpMdLya13UrfbLID3hR4hNwXReMpbOW ZsQoNmtg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1vVQPG-00000004vAl-09YM; Tue, 16 Dec 2025 08:27:42 +0000 Received: from tor.source.kernel.org ([172.105.4.254]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1vVQPE-00000004vAb-0P9p; Tue, 16 Dec 2025 08:27:40 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id 2922460173; Tue, 16 Dec 2025 08:27:39 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id CC4B5C4CEF1; Tue, 16 Dec 2025 08:27:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1765873658; bh=rE9Ya5hAlvxFBkqWRdp1h1Tw4atfvwW4q7E/otCHqMI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=JpH0ju1F8NUs3civI5pVZ0tGQuWRgVmJea/HUdFrdPkxzabRyvvWngSvPwbNCTYPM LJhIccwNtxPnFVZsJpjcpGl6URl9HoPyZlVGLkXNQioxIxUlUHqExaKN17uE1o+paN YIuIEHbyBtzPN2eAcDgL7HhmXY/jt4Sh4cJXRHafAOdEeo3X/RvSkX8KvfVxqYwkN0 JX856NBteLWPccrXuACAGyV7qGbQ2wZXIYL2a0xP9lOzCYR16+RdIzhXRdd/aRzbla ShNeBUsczzSfo6Dy7whFpMq3VOLTjncclOgtP5L92fUVPRhMUtuHyyH7Dk+zoItnnq rMHeQFc4RhbtA== Date: Tue, 16 Dec 2025 00:27:38 -0800 From: Kees Cook To: Ryan Roberts Cc: Catalin Marinas , Will Deacon , Huacai Chen , Madhavan Srinivasan , Michael Ellerman , Paul Walmsley , Palmer Dabbelt , Albert Ou , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "Gustavo A. R. Silva" , Arnd Bergmann , Mark Rutland , "Jason A. Donenfeld" , Ard Biesheuvel , Jeremy Linton , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, loongarch@lists.linux.dev, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-hardening@vger.kernel.org Subject: Re: [PATCH v2 3/3] randomize_kstack: Unify random source across arches Message-ID: <202512160024.B688A8D0@keescook> References: <20251215163520.1144179-1-ryan.roberts@arm.com> <20251215163520.1144179-4-ryan.roberts@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251215163520.1144179-4-ryan.roberts@arm.com> X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, Dec 15, 2025 at 04:35:17PM +0000, Ryan Roberts wrote: > [...] > @@ -45,9 +46,22 @@ DECLARE_STATIC_KEY_MAYBE(CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT, > #define KSTACK_OFFSET_MAX(x) ((x) & 0b1111111100) > #endif > > +DECLARE_PER_CPU(struct rnd_state, kstack_rnd_state); > + > +static __always_inline u32 get_kstack_offset(void) > +{ > + struct rnd_state *state; > + u32 rnd; > + > + state = &get_cpu_var(kstack_rnd_state); > + rnd = prandom_u32_state(state); > + put_cpu_var(kstack_rnd_state); > + > + return rnd; > +} > [...] > -static inline void random_kstack_task_init(struct task_struct *tsk) > +static int random_kstack_init(void) > { > - tsk->kstack_offset = 0; > + prandom_seed_full_state(&kstack_rnd_state); > + return 0; > } > + > +late_initcall(random_kstack_init); Doesn't this need to be run for every CPU? (And how does hotplug work for such things?) And doesn't it need a get_cpu_var? -- Kees Cook