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 A8A01D5CC89 for ; Tue, 16 Dec 2025 09:17:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:From:References:Cc:To: Subject:MIME-Version:Date:Message-ID:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=ohZpV8HyF4lhYTYKXOzp+F3x6ydSDNolFyss4DKU6qo=; b=w8j4z0+BK5oo51 gO9pH0t4jnj3MT/u8om3qwrNvxPPiRqisBDuOw4ESArsL5oIWmYHTXrJurIpmbu7qn3UlyjZzOXqN Q3UQzYkcIfH/csrtoYxmMAR4Xj9LbzmUjXKzMYOuCYjVC66B5sUtZR0qsFqrV0F7UlXImNjF6PXNw jYRCzENpd81H0Mbvkj1oI8eOuGuMTDgYCxhdy/w5ngWDWuF3wuCpwQLoUphgxiIvAO+U5k92YRnDY IcZ787nh49St0+3WRK7DBLPtPxulmBC8M9Az3hmaK1j76Qd2GVRB8PXDXCpruDizyovTG5p/dxEee pd/WrrXFXgzbadvWWeyw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1vVRB7-00000004yb5-1dcJ; Tue, 16 Dec 2025 09:17:09 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1vVRB4-00000004yaM-06g0; Tue, 16 Dec 2025 09:17:08 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id B6985FEC; Tue, 16 Dec 2025 01:16:57 -0800 (PST) Received: from [10.57.91.77] (unknown [10.57.91.77]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id E956C3F73B; Tue, 16 Dec 2025 01:16:59 -0800 (PST) Message-ID: <9ae8655f-e537-43bb-ae0e-3067d2481d79@arm.com> Date: Tue, 16 Dec 2025 09:16:58 +0000 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 3/3] randomize_kstack: Unify random source across arches Content-Language: en-GB To: Ard Biesheuvel , Kees Cook 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" , 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 References: <20251215163520.1144179-1-ryan.roberts@arm.com> <20251215163520.1144179-4-ryan.roberts@arm.com> <202512160024.B688A8D0@keescook> From: Ryan Roberts In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20251216_011706_114245_DA2F2F50 X-CRM114-Status: GOOD ( 13.44 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org On 16/12/2025 08:30, Ard Biesheuvel wrote: > On Tue, 16 Dec 2025 at 09:27, Kees Cook wrote: >> >> 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? >> > > > prandom_seed_full_state() takes a 'struct rnd_state __percpu > *pcpu_state', and performs the initialization for all possible CPUs. Yes, indeed, prandom_seed_full_state() is initializing all possible CPUs so it doesn't matter if it gets migrated. I believe this is correct as is. void prandom_seed_full_state(struct rnd_state __percpu *pcpu_state) { int i; for_each_possible_cpu(i) { struct rnd_state *state = per_cpu_ptr(pcpu_state, i); u32 seeds[4]; get_random_bytes(&seeds, sizeof(seeds)); state->s1 = __seed(seeds[0], 2U); state->s2 = __seed(seeds[1], 8U); state->s3 = __seed(seeds[2], 16U); state->s4 = __seed(seeds[3], 128U); prandom_warmup(state); } } _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv