From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.zytor.com (terminus.zytor.com [198.137.202.136]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 01DEB13F42C for ; Wed, 17 Apr 2024 15:56:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.137.202.136 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1713369377; cv=none; b=ahc6s0FlicrX3t+ReXCMDWWJq8GEk+Ul2OuiAI5VyE5GGAADoJE4YNuYD2rpMsvvPQGCKZOIMtJx5ayRKUxFvQ2x3T2JAOHbl5lAY1YjIIOXmoThYm6AS8e3UAu3zD1XEz75HultaQM+XWfJlqLaBvRIRR/Ji7J/gh2lg6uDaco= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1713369377; c=relaxed/simple; bh=MPK99SsBce6j62tVF0oHLjCbjiCnP7a4vsEqtMYYkVc=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=VGxA7nNvfeDewtyfgJN6FZNjNQUAm/wjtEZooFImcrlf10pfCI5cR9sgcqu23s3bX7sTDdtOiKCgznDLgFaiBa0LqF0RDDfuhwSFtrykSP1/oFLOC4ATNZ3mP+308kS1IHoITJQisovUOQdBmtsS1r7zzMYePzacPSQLu3NW0Qc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zytor.com; spf=pass smtp.mailfrom=zytor.com; dkim=pass (2048-bit key) header.d=zytor.com header.i=@zytor.com header.b=Ln0oW5qe; arc=none smtp.client-ip=198.137.202.136 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zytor.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=zytor.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=zytor.com header.i=@zytor.com header.b="Ln0oW5qe" Received: from [192.168.7.187] ([71.202.166.45]) (authenticated bits=0) by mail.zytor.com (8.17.2/8.17.1) with ESMTPSA id 43HFtmfv4097146 (version=TLSv1.3 cipher=TLS_AES_128_GCM_SHA256 bits=128 verify=NO); Wed, 17 Apr 2024 08:55:48 -0700 DKIM-Filter: OpenDKIM Filter v2.11.0 mail.zytor.com 43HFtmfv4097146 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zytor.com; s=2024041401; t=1713369349; bh=+fMU2l5Qou0wqC8gUqLaWi6h9YOjdUUx29qf3uYZ3w4=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=Ln0oW5qey22/25HToNAaUSsnAxcwT8Y1SRYPy5Ec9ERdrr92bXTZ7Tza2JsxtGbjh lCS8DP3o5kBCw0+0fNjZBxpdo08MoPdfRFYL3TR2uUf9z+9KBa53ug7H/NGImznhTX G1AkXExJgBWGB2nLd5elbZ2UruPXg5qGqQ6KRvMr6ZDLfGlGNYLl3rQWyc8O43rZYX b2dxlIb45Z27USbcTk0YKs6SUIa6MWysI5mAdEnncJRxOwuZOhrk8X7gV35o1SL1U+ ilYwpobiDc3F3dL4W7dNGeYNL7qud4jT+WGm/CCF5Gl/6S65+sf0vvuzrR0VMNZmyf UgDb8Tz4CGHcQ== Message-ID: <58272a50-fa74-4ae8-8ce2-aeb92a0f6ece@zytor.com> Date: Wed, 17 Apr 2024 08:55:46 -0700 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 v3 1/1] x86/fred: Fix INT80 emulation for FRED To: "H. Peter Anvin" , Nikolay Borisov , linux-kernel@vger.kernel.org Cc: luto@kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org References: <20240417063001.3773507-1-xin@zytor.com> <2d0e67dd-c3e3-4701-839a-68d73c61c170@zytor.com> Content-Language: en-US From: Xin Li Autocrypt: addr=xin@zytor.com; keydata= xsDNBGUPz1cBDACS/9yOJGojBFPxFt0OfTWuMl0uSgpwk37uRrFPTTLw4BaxhlFL0bjs6q+0 2OfG34R+a0ZCuj5c9vggUMoOLdDyA7yPVAJU0OX6lqpg6z/kyQg3t4jvajG6aCgwSDx5Kzg5 Rj3AXl8k2wb0jdqRB4RvaOPFiHNGgXCs5Pkux/qr0laeFIpzMKMootGa4kfURgPhRzUaM1vy bsMsL8vpJtGUmitrSqe5dVNBH00whLtPFM7IbzKURPUOkRRiusFAsw0a1ztCgoFczq6VfAVu raTye0L/VXwZd+aGi401V2tLsAHxxckRi9p3mc0jExPc60joK+aZPy6amwSCy5kAJ/AboYtY VmKIGKx1yx8POy6m+1lZ8C0q9b8eJ8kWPAR78PgT37FQWKYS1uAroG2wLdK7FiIEpPhCD+zH wlslo2ETbdKjrLIPNehQCOWrT32k8vFNEMLP5G/mmjfNj5sEf3IOKgMTMVl9AFjsINLHcxEQ 6T8nGbX/n3msP6A36FDfdSEAEQEAAc0WWGluIExpIDx4aW5Aenl0b3IuY29tPsLBDQQTAQgA NxYhBIUq/WFSDTiOvUIqv2u9DlcdrjdRBQJlD89XBQkFo5qAAhsDBAsJCAcFFQgJCgsFFgID AQAACgkQa70OVx2uN1HUpgv/cM2fsFCQodLArMTX5nt9yqAWgA5t1srri6EgS8W3F+3Kitge tYTBKu6j5BXuXaX3vyfCm+zajDJN77JHuYnpcKKr13VcZi1Swv6Jx1u0II8DOmoDYLb1Q2ZW v83W55fOWJ2g72x/UjVJBQ0sVjAngazU3ckc0TeNQlkcpSVGa/qBIHLfZraWtdrNAQT4A1fa sWGuJrChBFhtKbYXbUCu9AoYmmbQnsx2EWoJy3h7OjtfFapJbPZql+no5AJ3Mk9eE5oWyLH+ QWqtOeJM7kKvn/dBudokFSNhDUw06e7EoVPSJyUIMbYtUO7g2+Atu44G/EPP0yV0J4lRO6EA wYRXff7+I1jIWEHpj5EFVYO6SmBg7zF2illHEW31JAPtdDLDHYcZDfS41caEKOQIPsdzQkaQ oW2hchcjcMPAfyhhRzUpVHLPxLCetP8vrVhTvnaZUo0xaVYb3+wjP+D5j/3+hwblu2agPsaE vgVbZ8Fx3TUxUPCAdr/p73DGg57oHjgezsDNBGUPz1gBDAD4Mg7hMFRQqlzotcNSxatlAQNL MadLfUTFz8wUUa21LPLrHBkUwm8RujehJrzcVbPYwPXIO0uyL/F///CogMNx7Iwo6by43KOy g89wVFhyy237EY76j1lVfLzcMYmjBoTH95fJC/lVb5Whxil6KjSN/R/y3jfG1dPXfwAuZ/4N cMoOslWkfZKJeEut5aZTRepKKF54T5r49H9F7OFLyxrC/uI9UDttWqMxcWyCkHh0v1Di8176 jjYRNTrGEfYfGxSp+3jYL3PoNceIMkqM9haXjjGl0W1B4BidK1LVYBNov0rTEzyr0a1riUrp Qk+6z/LHxCM9lFFXnqH7KWeToTOPQebD2B/Ah5CZlft41i8L6LOF/LCuDBuYlu/fI2nuCc8d m4wwtkou1Y/kIwbEsE/6RQwRXUZhzO6llfoN96Fczr/RwvPIK5SVMixqWq4QGFAyK0m/1ap4 bhIRrdCLVQcgU4glo17vqfEaRcTW5SgX+pGs4KIPPBE5J/ABD6pBnUUAEQEAAcLA/AQYAQgA JhYhBIUq/WFSDTiOvUIqv2u9DlcdrjdRBQJlD89ZBQkFo5qAAhsMAAoJEGu9DlcdrjdR4C0L /RcjolEjoZW8VsyxWtXazQPnaRvzZ4vhmGOsCPr2BPtMlSwDzTlri8BBG1/3t/DNK4JLuwEj OAIE3fkkm+UG4Kjud6aNeraDI52DRVCSx6xff3bjmJsJJMb12mWglN6LjdF6K+PE+OTJUh2F dOhslN5C2kgl0dvUuevwMgQF3IljLmi/6APKYJHjkJpu1E6luZec/lRbetHuNFtbh3xgFIJx 2RpgVDP4xB3f8r0I+y6ua+p7fgOjDLyoFjubRGed0Be45JJQEn7A3CSb6Xu7NYobnxfkwAGZ Q81a2XtvNS7Aj6NWVoOQB5KbM4yosO5+Me1V1SkX2jlnn26JPEvbV3KRFcwV5RnDxm4OQTSk PYbAkjBbm+tuJ/Sm+5Yp5T/BnKz21FoCS8uvTiziHj2H7Cuekn6F8EYhegONm+RVg3vikOpn gao85i4HwQTK9/D1wgJIQkdwWXVMZ6q/OALaBp82vQ2U9sjTyFXgDjglgh00VRAHP7u1Rcu4 l75w1xInsg== In-Reply-To: <2d0e67dd-c3e3-4701-839a-68d73c61c170@zytor.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 4/17/2024 8:07 AM, H. Peter Anvin wrote: > On 4/17/24 04:02, Nikolay Borisov wrote: >> >> On 17.04.24 г. 9:30 ч., Xin Li (Intel) wrote: >>> 4) int80_emulation() does a CLEAR_BRANCH_HISTORY, which is likely >>> >     overkill for new x86 CPU implementations that support FRED. >> >> Well, that's a bit of an overstatement/speculation, because >> clear_branch_history will only be effective if the machine is >> susceptible to the given bug and there isn't a better options (i.e >> using a hardware bit controlling the respective aspect of the CPU). >>> > > It would seem like a huge stretch to expect that a FRED-capable CPU > would not have such a facility. This is a matter of establishing a > baseline for FRED-capable hardware. > > It would make more sense to me to add it if we turn out to need it; note > that FRED code is currently only enabled on demand, in order to defend > against bit rot until we have physical hardware. > > Now, if this is still desired, it *probably* belongs better in either > fred_intx()/fred_other() or asm_fred_entrypoint_user, depending on if > this ought to be done for all entries from userspace or only system calls. My bad that I didn't make this a good comment, even neglected that clear_branch_history is just a nop on machines w/o such security issues. So how about? int80_emulation() does a CLEAR_BRANCH_HISTORY, which is IDT-specific. While FRED will likely take a different approach when it is needed: it *probably* belongs in either fred_intx()/fred_other() or asm_fred_entrypoint_user(), depending on if this ought to be done for all entries from userspace or only system calls.