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 4D680CA5FA8 for ; Tue, 20 Jan 2026 16:32:35 +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=pzCqaWRw4l8YZiXRlEaKsY2UZqzEryF7b+9WjJwCLVI=; b=SdY6uEQKzKK0a7aNGPT3Wo/pkO GnUT/JQpdT2J95pTYdjv/vz2Vz4fEZe1bGMcgaQkheOwmdbcDtKWvc4MpjnP1KdAiwIj/hwjMY9gz /63G6bXWQNPpKOO3DXV1GVDNOxN95PFfM8UkUbfYtaGBWr+8N2eR+XwHBb4dDIp70lFRkb+u468Eq 8e8UeXcLzVExs84SAMtzQS5emPwNlWrm1683mPe9FFi0Ph5LaNwU38r8ax9g/mHRtDG7ewOmHGsEj N7CwUL/c0kgc01XHaFfcPmAD4F8kvrGrvpfTNm5WBjque/gWMsJcgdqyQc7edUZW52D/qOfKJe0T7 7kJEeUfw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1viEeb-00000004ApR-31Nn; Tue, 20 Jan 2026 16:32:29 +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 1viEeX-00000004AoO-1XbN; Tue, 20 Jan 2026 16:32:26 +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 6B3771476; Tue, 20 Jan 2026 08:32:16 -0800 (PST) Received: from [10.1.39.200] (XHFQ2J9959.cambridge.arm.com [10.1.39.200]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id BFE823F694; Tue, 20 Jan 2026 08:32:18 -0800 (PST) Message-ID: <785a7d90-babe-43af-93a6-c220c1877bcf@arm.com> Date: Tue, 20 Jan 2026 16:32:17 +0000 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 0/3] Fix bugs and performance of kstack offset randomisation Content-Language: en-GB To: Kees Cook , Dave Hansen , 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 , David Laight Cc: 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: <20260119130122.1283821-1-ryan.roberts@arm.com> <20fb97f1-7e50-485a-bdfd-a2901d20ec84@intel.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-20260120_083225_449484_344D2076 X-CRM114-Status: GOOD ( 16.96 ) 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 19/01/2026 16:44, Kees Cook wrote: > > > On January 19, 2026 8:00:00 AM PST, Dave Hansen wrote: >> On 1/19/26 05:01, Ryan Roberts wrote: >>> x86 (AWS Sapphire Rapids): >>> +-----------------+--------------+-------------+---------------+ >>> | Benchmark | Result Class | v6.18-rc5 | per-task-prng | >>> | | | rndstack-on | | >>> | | | | | >>> +=================+==============+=============+===============+ >>> | syscall/getpid | mean (ns) | (R) 13.32% | (R) 4.60% | >>> | | p99 (ns) | (R) 13.38% | (R) 18.08% | >>> | | p99.9 (ns) | 16.26% | (R) 19.38% | >> >> Like you noted, this is surprising. This would be a good thing to make >> sure it goes in very early after -rc1 and gets plenty of wide testing. > > Right, we are pretty late in the dev cycle (rc6). It would be prudent to get this into -next after the coming rc1 (1 month from now). > > On the other hand, the changes are pretty "binary" in the sense that mistakes should be VERY visible right away. Would it be better to take this into -next immediately instead? I don't think this question was really addressed to me, but I'll give my opinion anyway; I agree it's pretty binary - it will either work or it will explode. I've tested on arm64 and x86_64 so I have high confidence that it works. If you get it into -next ASAP it has 3 weeks to soak before the merge window opens right? (Linus said he would do an -rc8 this cycle). That feels like enough time to me. But it's your tree ;-) Thanks, Ryan > >> But I don't see any problems with the approach, and the move to common >> code looks like a big win as well: > > Agreed; I think it's looking great. >