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 4C4437FBC4; Wed, 21 Feb 2024 16:55:05 +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=1708534509; cv=none; b=TP19tpH6hozl45z1lL0ZSQYzyw4KHPBGdHLn5/TYqEZ4qlTGZpJt7ODCxble/4fSac2yyuDhUgq3EEf6jnaF9tIs+GbH2N7/aERh3AYQeFK41NLFCQCbSHdZx7W7i9x3Q86cglOQrq2mqHr0JA1+0YOLzD3XDZZqFHK6syHsXzw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708534509; c=relaxed/simple; bh=07lkd9NoppxxiEpP29PS7z0+eMrgeWwUwan7L7s+lZE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=EkcFzvmKN0TGsdtQUBZNapr7Z2CsXn/zdpaDzhKekosed8hcwdSC4/bSVSj4fChBDBx4HU2vrA1o2waq98w9VtlLreMucP6FFYRy6c02yVDCFl/J2fkEydire2eFtlcyXw9kmNanOTo71Ig1qmgGNrDeVgkCEV2oPTu49JmNdas= 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 2D0611007; Wed, 21 Feb 2024 08:55:43 -0800 (PST) Received: from [192.168.20.13] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id B5F143F73F; Wed, 21 Feb 2024 08:55:00 -0800 (PST) Message-ID: <305d26ba-8738-4244-801f-939e1a9730a1@arm.com> Date: Wed, 21 Feb 2024 10:54:58 -0600 Precedence: bulk X-Mailing-List: linux-hardening@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC] arm64: syscall: Direct PRNG kstack randomization Content-Language: en-US To: "Jason A. Donenfeld" , Kees Cook Cc: linux-arm-kernel@lists.infradead.org, catalin.marinas@arm.com, will@kernel.org, gustavoars@kernel.org, mark.rutland@arm.com, rostedt@goodmis.org, arnd@arndb.de, broonie@kernel.org, guohui@uniontech.com, Manoj.Iyer@arm.com, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org, James Yang , Shiyou Huang References: <20240221020258.1210148-1-jeremy.linton@arm.com> <202402202226.A6817927@keescook> From: Jeremy Linton In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Hi, Thanks for looking at this. On 2/21/24 06:44, Jason A. Donenfeld wrote: > Hi, > > On Wed, Feb 21, 2024 at 7:33 AM Kees Cook wrote: >>> +#ifdef CONFIG_RANDOMIZE_KSTACK_OFFSET >>> +DEFINE_PER_CPU(u32, kstackrng); >>> +static u32 xorshift32(u32 state) >>> +{ >>> + /* >>> + * From top of page 4 of Marsaglia, "Xorshift RNGs" >>> + * This algorithm is intended to have a period 2^32 -1 >>> + * And should not be used anywhere else outside of this >>> + * code path. >>> + */ >>> + state ^= state << 13; >>> + state ^= state >> 17; >>> + state ^= state << 5; >>> + return state; >>> +} > > Can we please *not* introduce yet another RNG? You can't just sprinkle > this stuff all over the place with no rhyme or reason. > > If you need repeatable randomness, use prandom_u32_state() or similar. > If you need non-repeatable randomness, use get_random_bytes() or > similar. Sure prandom_u32_state() should have a similar effect being a bit slower, and a bit better due to the extra hidden state. > > If you think prandom_u32_state() is insufficient for some reason or > doesn't have some property or performance that you want, submit a > patch to make it better. > > Looking at the actual intention here, of using repeatable randomness, > I find the intent pretty weird. Isn't the whole point of kstack > randomization that you can't predict it? If so, get_random_u*() is > what you want. If performance isn't sufficient, let's figure out some There isn't anything wrong with get_random_u16 from a kstack randomization standpoint, except for the latency spikes of course. > way to improve performance. And as Kees said, if the point of this is > to have some repeatable benchmarks, maybe just don't enable the > security-intended code whose purpose is non-determinism? Both exploits > and now apparently benchmarks like determinism. As I mentioned in the other email, benchmark is probably the wrong word. Its a better QoS response time distributions for a given workload. And its not strictly in RT kernel latency test types of things, but normal memcached style workloads on !RT kernels as well. 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 9271EC5478A for ; Wed, 21 Feb 2024 16:55:21 +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-Type: Content-Transfer-Encoding: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=OMjdZcZIRLuF/DdRrJWHNkqHPdPg6VNVmqDQAvKt/Tg=; b=4Tc95X55z02+CR UYa4OvTwzKpMGAXVmjiDA0AwIkK44cONz3cFalhiCJQLNWNDybYooRMMBlSh+k8MUgxZ+9SoP/diX f12cdnRHnVQonNx5RggJ3J/vaXn80SSoVgubWZucf+sH6oF6F8GA50wrD2BaK7aKm/F8UxWuW8upk KdLR+VaGFPrthWnv2DzIc1Kqo36Hd/Jdjtk44c+fRmLbB5yR8yZ+oCe28pPhFBjbSTSbl8xUHvwSz 8IV4L3PPBBwurVhSJjg3kVetQ1ZL+5Bz4QMlVV/Y6i9iX0rtRCEkMKn9M+Esh4crYPGKAMU7dqER2 UbEpQ9yyk2toOg4hSqNA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1rcpsE-00000001o2J-0JnM; Wed, 21 Feb 2024 16:55:10 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1rcpsB-00000001o1k-1x47 for linux-arm-kernel@lists.infradead.org; Wed, 21 Feb 2024 16:55:08 +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 2D0611007; Wed, 21 Feb 2024 08:55:43 -0800 (PST) Received: from [192.168.20.13] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id B5F143F73F; Wed, 21 Feb 2024 08:55:00 -0800 (PST) Message-ID: <305d26ba-8738-4244-801f-939e1a9730a1@arm.com> Date: Wed, 21 Feb 2024 10:54:58 -0600 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC] arm64: syscall: Direct PRNG kstack randomization Content-Language: en-US To: "Jason A. Donenfeld" , Kees Cook Cc: linux-arm-kernel@lists.infradead.org, catalin.marinas@arm.com, will@kernel.org, gustavoars@kernel.org, mark.rutland@arm.com, rostedt@goodmis.org, arnd@arndb.de, broonie@kernel.org, guohui@uniontech.com, Manoj.Iyer@arm.com, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org, James Yang , Shiyou Huang References: <20240221020258.1210148-1-jeremy.linton@arm.com> <202402202226.A6817927@keescook> From: Jeremy Linton In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240221_085507_572602_63821C50 X-CRM114-Status: GOOD ( 20.35 ) 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: , Content-Transfer-Encoding: base64 Content-Type: text/plain; charset="utf-8"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org SGksCgpUaGFua3MgZm9yIGxvb2tpbmcgYXQgdGhpcy4KCk9uIDIvMjEvMjQgMDY6NDQsIEphc29u IEEuIERvbmVuZmVsZCB3cm90ZToKPiBIaSwKPiAKPiBPbiBXZWQsIEZlYiAyMSwgMjAyNCBhdCA3 OjMz4oCvQU0gS2VlcyBDb29rIDxrZWVzY29va0BjaHJvbWl1bS5vcmc+IHdyb3RlOgo+Pj4gKyNp ZmRlZiBDT05GSUdfUkFORE9NSVpFX0tTVEFDS19PRkZTRVQKPj4+ICtERUZJTkVfUEVSX0NQVSh1 MzIsIGtzdGFja3JuZyk7Cj4+PiArc3RhdGljIHUzMiB4b3JzaGlmdDMyKHUzMiBzdGF0ZSkKPj4+ ICt7Cj4+PiArICAgICAvKgo+Pj4gKyAgICAgICogRnJvbSB0b3Agb2YgcGFnZSA0IG9mIE1hcnNh Z2xpYSwgIlhvcnNoaWZ0IFJOR3MiCj4+PiArICAgICAgKiBUaGlzIGFsZ29yaXRobSBpcyBpbnRl bmRlZCB0byBoYXZlIGEgcGVyaW9kIDJeMzIgLTEKPj4+ICsgICAgICAqIEFuZCBzaG91bGQgbm90 IGJlIHVzZWQgYW55d2hlcmUgZWxzZSBvdXRzaWRlIG9mIHRoaXMKPj4+ICsgICAgICAqIGNvZGUg cGF0aC4KPj4+ICsgICAgICAqLwo+Pj4gKyAgICAgc3RhdGUgXj0gc3RhdGUgPDwgMTM7Cj4+PiAr ICAgICBzdGF0ZSBePSBzdGF0ZSA+PiAxNzsKPj4+ICsgICAgIHN0YXRlIF49IHN0YXRlIDw8IDU7 Cj4+PiArICAgICByZXR1cm4gc3RhdGU7Cj4+PiArfQo+IAo+IENhbiB3ZSBwbGVhc2UgKm5vdCog aW50cm9kdWNlIHlldCBhbm90aGVyIFJORz8gWW91IGNhbid0IGp1c3Qgc3ByaW5rbGUKPiB0aGlz IHN0dWZmIGFsbCBvdmVyIHRoZSBwbGFjZSB3aXRoIG5vIHJoeW1lIG9yIHJlYXNvbi4KPiAKPiBJ ZiB5b3UgbmVlZCByZXBlYXRhYmxlIHJhbmRvbW5lc3MsIHVzZSBwcmFuZG9tX3UzMl9zdGF0ZSgp IG9yIHNpbWlsYXIuCj4gSWYgeW91IG5lZWQgbm9uLXJlcGVhdGFibGUgcmFuZG9tbmVzcywgdXNl IGdldF9yYW5kb21fYnl0ZXMoKSBvcgo+IHNpbWlsYXIuCgpTdXJlIHByYW5kb21fdTMyX3N0YXRl KCkgc2hvdWxkIGhhdmUgYSBzaW1pbGFyIGVmZmVjdCBiZWluZyBhIGJpdCAKc2xvd2VyLCBhbmQg YSBiaXQgYmV0dGVyIGR1ZSB0byB0aGUgZXh0cmEgaGlkZGVuIHN0YXRlLgoKPiAKPiBJZiB5b3Ug dGhpbmsgcHJhbmRvbV91MzJfc3RhdGUoKSBpcyBpbnN1ZmZpY2llbnQgZm9yIHNvbWUgcmVhc29u IG9yCj4gZG9lc24ndCBoYXZlIHNvbWUgcHJvcGVydHkgb3IgcGVyZm9ybWFuY2UgdGhhdCB5b3Ug d2FudCwgc3VibWl0IGEKPiBwYXRjaCB0byBtYWtlIGl0IGJldHRlci4KPiAKPiBMb29raW5nIGF0 IHRoZSBhY3R1YWwgaW50ZW50aW9uIGhlcmUsIG9mIHVzaW5nIHJlcGVhdGFibGUgcmFuZG9tbmVz cywKPiBJIGZpbmQgdGhlIGludGVudCBwcmV0dHkgd2VpcmQuIElzbid0IHRoZSB3aG9sZSBwb2lu dCBvZiBrc3RhY2sKPiByYW5kb21pemF0aW9uIHRoYXQgeW91IGNhbid0IHByZWRpY3QgaXQ/IElm IHNvLCBnZXRfcmFuZG9tX3UqKCkgaXMKPiB3aGF0IHlvdSB3YW50LiBJZiBwZXJmb3JtYW5jZSBp c24ndCBzdWZmaWNpZW50LCBsZXQncyBmaWd1cmUgb3V0IHNvbWUKClRoZXJlIGlzbid0IGFueXRo aW5nIHdyb25nIHdpdGggZ2V0X3JhbmRvbV91MTYgZnJvbSBhIGtzdGFjayAKcmFuZG9taXphdGlv biBzdGFuZHBvaW50LCBleGNlcHQgZm9yIHRoZSBsYXRlbmN5IHNwaWtlcyBvZiBjb3Vyc2UuCgo+ IHdheSB0byBpbXByb3ZlIHBlcmZvcm1hbmNlLiBBbmQgYXMgS2VlcyBzYWlkLCBpZiB0aGUgcG9p bnQgb2YgdGhpcyBpcwo+IHRvIGhhdmUgc29tZSByZXBlYXRhYmxlIGJlbmNobWFya3MsIG1heWJl IGp1c3QgZG9uJ3QgZW5hYmxlIHRoZQo+IHNlY3VyaXR5LWludGVuZGVkIGNvZGUgd2hvc2UgcHVy cG9zZSBpcyBub24tZGV0ZXJtaW5pc20/IEJvdGggZXhwbG9pdHMKPiBhbmQgbm93IGFwcGFyZW50 bHkgYmVuY2htYXJrcyBsaWtlIGRldGVybWluaXNtLgoKQXMgSSBtZW50aW9uZWQgaW4gdGhlIG90 aGVyIGVtYWlsLCBiZW5jaG1hcmsgaXMgcHJvYmFibHkgdGhlIHdyb25nIHdvcmQuIApJdHMgYSBi ZXR0ZXIgUW9TIHJlc3BvbnNlIHRpbWUgZGlzdHJpYnV0aW9ucyBmb3IgYSBnaXZlbiB3b3JrbG9h ZC4gQW5kIAppdHMgbm90IHN0cmljdGx5IGluIFJUIGtlcm5lbCBsYXRlbmN5IHRlc3QgdHlwZXMg b2YgdGhpbmdzLCBidXQgbm9ybWFsIAptZW1jYWNoZWQgc3R5bGUgd29ya2xvYWRzIG9uICFSVCBr ZXJuZWxzIGFzIHdlbGwuCgoKCl9fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19f X19fX19fX19fCmxpbnV4LWFybS1rZXJuZWwgbWFpbGluZyBsaXN0CmxpbnV4LWFybS1rZXJuZWxA bGlzdHMuaW5mcmFkZWFkLm9yZwpodHRwOi8vbGlzdHMuaW5mcmFkZWFkLm9yZy9tYWlsbWFuL2xp c3RpbmZvL2xpbnV4LWFybS1rZXJuZWwK