From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id C73103176EF; Tue, 20 Jan 2026 16:32:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768926745; cv=none; b=Az4bBswOAiOabmyu6WCBgHETI7upMzsyzQsan/1B8AE/NQxUKp/bPQZHw0iU/L+sK5VQkZelpp7IKzg94SX7qEtsHmtZmmKuodpJUH3aPYY/FhfSwPESs5wS6sSJrjmCKCzwqCk8O1zNftjqWFOrAQ4ucJ/z4TIGfH9o2HDCgns= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768926745; c=relaxed/simple; bh=MEfEaETuHARVD48KyuQmVhFNmOwX8YQiQSJrURCh6EY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=JcZT4IhpB/ECiyrEGGkGtMkhSWGhXL/+cgSPIu6029kRkiV3tbzz8cRy5jlwEBdjkGlRyNFn6OG80GewPNRal2yX/k5eYAg+51clwk7GSY3LN3moz8FTQsLsAGLqXkg601GccP8iyfqTux9H8MSGOYkUxkG6h3FjeJxx/j6voYA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com 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 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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 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. >