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 lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (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 CE6A9D5C0D1 for ; Tue, 16 Dec 2025 08:28:13 +0000 (UTC) Received: from boromir.ozlabs.org (localhost [127.0.0.1]) by lists.ozlabs.org (Postfix) with ESMTP id 4dVqnS3jY8z2yDY; Tue, 16 Dec 2025 19:28:12 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; arc=none smtp.remote-ip=172.105.4.254 ARC-Seal: i=1; a=rsa-sha256; d=lists.ozlabs.org; s=201707; t=1765873692; cv=none; b=XwyDLrJzjzwgBOk0Fb6uyWdHrQEtiqCGDghOWF2SOwNKujPHvYHda6SmOs1oMUe+jeyHgIZZwyiwUjzBzwAcaNZV7wv18uyeUYsha2GBwBSU4LgGC8F9+adEJ8fo6RYehiFoKEnZXxZvwXvoO3rlD/LZBdVPA89C/FkcZxOLvpWZo9KBpbVptBkf6uDJdGZQ9VKNN/j1cmQeWp0BCn5w6aq6HrhBIUttnduagCapj5D7sNsO2s1uY3Szjl4Lpup1ecPXxysTWvRi2MVQB476ZrGBLKXP1Iom7hUUAEpgCm14dUXeK5HT3gVsT5Th+4Hok8ULxAQzIxNeo6HZcIFZ2A== ARC-Message-Signature: i=1; a=rsa-sha256; d=lists.ozlabs.org; s=201707; t=1765873692; c=relaxed/relaxed; bh=18QUzibWbUvzdO3mSa7PVgq3DCScRHDw8cH0GYL+t4Q=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=jc92AefNcoi+E74jt2+T7rvwSjcctv2zjRIJZrYyxs4i80a9lL/4UArBpYsbllj9eFy07trO8r3Jv6L02Ur+qk7gxEOvgSae23PCO79kuwTc0/CacyGLgDpWrPgXMIXwIsFF1qHebzF0/oq55NTvl0tMTjX2abIBFr8sYI1AW+/FLWRXxdepJnAK2h26xiagUcod0bUDzs67xmvUgvecIYJUBkmAebop4d9yXwasRyMQHYwFJDWS0m5shuG55wXdABmLTFOXT/ssZnojPGTO33Xv+Cd1vlz6m7HhRAwLHcxzr4vO9vDiPHpMqQJkfvlKSYaVSqJmlV1I+fZo3mDOwg== ARC-Authentication-Results: i=1; lists.ozlabs.org; dmarc=pass (p=quarantine dis=none) header.from=kernel.org; dkim=pass (2048-bit key; unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20201202 header.b=JpH0ju1F; dkim-atps=neutral; spf=pass (client-ip=172.105.4.254; helo=tor.source.kernel.org; envelope-from=kees@kernel.org; receiver=lists.ozlabs.org) smtp.mailfrom=kernel.org Authentication-Results: lists.ozlabs.org; dmarc=pass (p=quarantine dis=none) header.from=kernel.org Authentication-Results: lists.ozlabs.org; dkim=pass (2048-bit key; unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20201202 header.b=JpH0ju1F; dkim-atps=neutral Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=kernel.org (client-ip=172.105.4.254; helo=tor.source.kernel.org; envelope-from=kees@kernel.org; receiver=lists.ozlabs.org) Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange x25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4dVqnR5gdsz2xqf for ; Tue, 16 Dec 2025 19:28:11 +1100 (AEDT) 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> X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251215163520.1144179-4-ryan.roberts@arm.com> 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