From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AH8x224/nIeK6rPnY1Ti02xZiurFXYcjuyDGApfkFu9MB8ylzgnw/a3R5det6GzglAVamEnXKsHZ ARC-Seal: i=1; a=rsa-sha256; t=1516918851; cv=none; d=google.com; s=arc-20160816; b=zZsVYYaS2qEyGkI2/+fiZ0ZGJIIf1BL/xl9AANQkk2G3yEpPT4BQFFred8Ic3mE6BX j54ACfwvFRwZFsRfuIDo0pUT2AXj5Nt7gXmpWo+Rg/9RUXR9D9Yd+Da+V1aE975n0Aob Y/F62l6Lp6ypKhMPYT+b0X8CVVKzqV3Nu6yjq1fzNpOF6f3AULxW8qg8Ir2fBUzH2LaM 3EUbHqtrCjGRSzfQpbp45hZZKWfokTCCdBX3N0qex3TpcPelLqvlVj/hP1u6OP8+cg/G PtKkjmRHQL4JZNHOl8SzOXy5VsAAfmHA4xHJxE2Re5J8uGBod2o6CCQ1xJduou2L6rEe dQ4Q== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=content-transfer-encoding:content-language:in-reply-to:mime-version :user-agent:date:message-id:from:cc:references:to:subject :arc-authentication-results; bh=2DEnHoV5vUSARJDDWz9rKZjutaekAPvmQQJUm0UcNuM=; b=grN6dadoa/zmDko9rGL6OGMVMn/Y8385L8zSAmfRbJUJyu6FlNUjmm1Xh0dDrjEK31 seCS4dlkkbWQiy9KVVH7D1UlwL6clqqNukJQp4enCn7d36VTDoF+0ZXupNNmic+uLwui SNHTbAmaULZlPu+GFSpBpcp6Q8fglGZjynu0jaOWwMihOzEYytfYivQ9wgM+HYj6NiqG Zmmzb2CJEkb7GOYsW1EaNz36Ax9lR14fhJPhdqXaSTsLHXD1QnDFyu286z4rDpPRajzz /K+a6zcTjKQlVEekmwchB8SgD9e0AfrOicS+P+qR4Vd4LXcnd1hqE4N8cdjcAQoApSBN 6YnQ== ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: domain of dave.hansen@intel.com designates 134.134.136.20 as permitted sender) smtp.mailfrom=dave.hansen@intel.com Authentication-Results: mx.google.com; spf=pass (google.com: domain of dave.hansen@intel.com designates 134.134.136.20 as permitted sender) smtp.mailfrom=dave.hansen@intel.com X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.46,413,1511856000"; d="scan'208";a="26395293" Subject: Re: [RFC 09/10] x86/enter: Create macros to restrict/unrestrict Indirect Branch Speculation To: Liran Alon , dwmw2@infradead.org References: <6c16fc37-bdf2-4925-8114-14f5a08c07e3@default> Cc: labbott@redhat.com, luto@kernel.org, Janakarajan.Natarajan@amd.com, torvalds@linux-foundation.org, bp@suse.de, asit.k.mallick@intel.com, rkrcmar@redhat.com, karahmed@amazon.de, hpa@zytor.com, mingo@redhat.com, jun.nakajima@intel.com, x86@kernel.org, ashok.raj@intel.com, arjan.van.de.ven@intel.com, tim.c.chen@linux.intel.com, pbonzini@redhat.com, ak@linux.intel.com, linux-kernel@vger.kernel.org, peterz@infradead.org, tglx@linutronix.de, gregkh@linuxfoundation.org, mhiramat@kernel.org, arjan@linux.intel.com, thomas.lendacky@amd.com, dan.j.williams@intel.com, joro@8bytes.org, kvm@vger.kernel.org, aarcange@redhat.com From: Dave Hansen Message-ID: <199a5883-42c7-d25c-0756-c3d4dcdc63ff@intel.com> Date: Thu, 25 Jan 2018 14:20:49 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.0 MIME-Version: 1.0 In-Reply-To: <6c16fc37-bdf2-4925-8114-14f5a08c07e3@default> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1590140582166248265?= X-GMAIL-MSGID: =?utf-8?q?1590604701298580980?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On 01/23/2018 03:13 AM, Liran Alon wrote: > Therefore, breaking KASLR. In order to handle this, every exit from > kernel-mode to user-mode should stuff RSB. In addition, this stuffing > of RSB may need to be done from a fixed address to avoid leaking the > address of the RSB stuffing itself. With PTI alone in place, I don't see how userspace could do anything with this information. Even if userspace started to speculate to a kernel address, there is nothing at the kernel address to execute: no TLB entry, no PTE to load, nothing. You probably have a valid point about host->guest, though.