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 19BDCCFD376 for ; Tue, 2 Dec 2025 11:04:23 +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:Content-Transfer-Encoding: Content-Type: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=5LgNM6Q7iy88HUI3l9HehvAGMJlgQwfWo+LouwfdJA8=; b=LCvOqk1yKr4CHwswufNqB2GoUF Avxjr4SnZ0S/wAQOwx56jLlHyAWwfljKAeHP5a8t20oMSEtyB0Jn7XLvA37eeM8uilJBms8699xsL pH5DX8JtpdBviV8EPqZaq8H8beN5kCrwhHDA92MwA9tGf5qb1SbReMqfKgclc47Xh5er2Pucrv7Np yYyX30yqqAuVAyknOmtt0Du3UKu9NGgfvnHzSEnVIh641cpw31o9iBuRC45U4jeMP+P9/+kdotg/k 6l6h7C4ZLQW5Z4tsaMiAkGMPy4Ju77pbKmZi69wvKShiOwsUrRhwptPQqcWeDFMR9HsB4YY0kHL2w CmDlwJ3w==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1vQOB7-00000005IIe-1gC8; Tue, 02 Dec 2025 11:04:17 +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 1vQOB4-00000005II2-3sTj for linux-arm-kernel@lists.infradead.org; Tue, 02 Dec 2025 11:04:16 +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 963B5153B; Tue, 2 Dec 2025 03:04:05 -0800 (PST) Received: from [10.1.30.224] (XHFQ2J9959.cambridge.arm.com [10.1.30.224]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 081833F59E; Tue, 2 Dec 2025 03:04:10 -0800 (PST) Message-ID: <684115c9-4ca2-485e-94a4-706d075f3f6e@arm.com> Date: Tue, 2 Dec 2025 11:04:09 +0000 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v1 2/2] randomize_kstack: Unify random source across arches Content-Language: en-GB To: Mark Rutland Cc: Ard Biesheuvel , Kees Cook , Ard Biesheuvel , Will Deacon , Arnd Bergmann , Jeremy Linton , Catalin Marinas , "Jason A . Donenfeld" , linux-hardening@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <20251127105958.2427758-1-ryan.roberts@arm.com> <20251127105958.2427758-3-ryan.roberts@arm.com> <9097505d-b18b-4f85-a02c-7f2865ad8bca@arm.com> <7da8d5cc-7b67-4f51-8f09-7ca401d06a3d@arm.com> From: Ryan Roberts In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20251202_030415_087276_2DF61DB7 X-CRM114-Status: GOOD ( 17.12 ) 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 02/12/2025 09:53, Mark Rutland wrote: > On Tue, Dec 02, 2025 at 09:39:40AM +0000, Ryan Roberts wrote: >> On 02/12/2025 09:35, Mark Rutland wrote: >>> On Tue, Dec 02, 2025 at 10:15:22AM +0100, Ard Biesheuvel wrote: >>>> On Mon, 1 Dec 2025 at 19:20, Ryan Roberts wrote: >>>>> On 28/11/2025 11:01, Ard Biesheuvel wrote: >>>>>> On Thu, 27 Nov 2025 at 12:00, Ryan Roberts wrote: >>>>>>> diff --git a/include/linux/randomize_kstack.h b/include/linux/randomize_kstack.h >>>>>>> index 089b1432f7e6..83c7e6710f6d 100644 >>>>>>> --- a/include/linux/randomize_kstack.h >>>>>>> +++ b/include/linux/randomize_kstack.h >>>>>>> @@ -6,6 +6,7 @@ >>>>>>> #include >>>>>>> #include >>>>>>> #include >>>>>>> +#include >>>>>>> >>>>>>> DECLARE_STATIC_KEY_MAYBE(CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT, >>>>>>> randomize_kstack_offset); >>>>>>> @@ -45,9 +46,13 @@ DECLARE_STATIC_KEY_MAYBE(CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT, >>>>>>> #define KSTACK_OFFSET_MAX(x) ((x) & 0b1111111100) >>>>>>> #endif >>>>>>> >>>>>>> +static __always_inline u32 get_update_kstack_offset(void) >>>>>>> +{ >>>>>>> + return prandom_u32_state(¤t->kstack_rnd_state); >>>>> >>>>> I've got bot warnings because this is being called from noinstr code. I guess >>>>> the best option is to just move add_random_kstack_offset() to after >>>>> instrumentation is enabled for the affected arches. >>>> >>>> Just put instrumentation_begin()/instrumentation_end() around the call >>>> to prandom_u32_state() - that seems to be the common approach for >>>> punching holes into the 'noinstr' validation. >>> >>> That silences the warning, but isn't necessarily safe, so please DO NOT >>> do that blindly. The instrumentation_{begin,end}() annotations are only >>> supposed to be used when we know by construction that instrumentation is >>> safe. >>> >>> Generally, if you can move this to after instrumentation is already >>> enabled, that should be safe, and so that'd be the better approach. >>> >>> Ryan, can you share those warnings (e.g. link to those reports)? >> >> https://lore.kernel.org/oe-kbuild-all/202511302137.u4iIA2kf-lkp@intel.com/ >> https://lore.kernel.org/oe-kbuild-all/202511302317.BGFIlAYX-lkp@intel.com/ > > Cool, so those are __do_fast_syscall_32() and do_syscall_64(), which I'd > expect (and those are legitimate warnings). > > From a quick scan of v6.18, it looks like arm64, loongarch, powerpc, and > riscv perform all the necessary entry work before calling > add_random_kstack_offset(), and we'll need to change: > > * s390's __do_syscall() > * x86's do_syscall_64() > * x86's do_int80_syscall_32() > * x86's __do_fast_syscall_32() Yup. I'll have a play with inline vs outline. If I go with outline, I'll fix these sites up. > > Mark.