From owner-dev-commits-src-main@freebsd.org Thu Aug 26 16:09:48 2021 Return-Path: Delivered-To: dev-commits-src-main@mailman.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.nyi.freebsd.org (Postfix) with ESMTP id 7DB5266C61A; Thu, 26 Aug 2021 16:09:48 +0000 (UTC) (envelope-from git@FreeBSD.org) Received: from mxrelay.nyi.freebsd.org (mxrelay.nyi.freebsd.org [IPv6:2610:1c1:1:606c::19:3]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256 client-signature RSA-PSS (4096 bits) client-digest SHA256) (Client CN "mxrelay.nyi.freebsd.org", Issuer "R3" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 4GwSV42tfBz3tv3; Thu, 26 Aug 2021 16:09:48 +0000 (UTC) (envelope-from git@FreeBSD.org) Received: from gitrepo.freebsd.org (gitrepo.freebsd.org [IPv6:2610:1c1:1:6068::e6a:5]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (Client did not present a certificate) by mxrelay.nyi.freebsd.org (Postfix) with ESMTPS id 4BCA312F73; Thu, 26 Aug 2021 16:09:48 +0000 (UTC) (envelope-from git@FreeBSD.org) Received: from gitrepo.freebsd.org ([127.0.1.44]) by gitrepo.freebsd.org (8.16.1/8.16.1) with ESMTP id 17QG9mgu005367; Thu, 26 Aug 2021 16:09:48 GMT (envelope-from git@gitrepo.freebsd.org) Received: (from git@localhost) by gitrepo.freebsd.org (8.16.1/8.16.1/Submit) id 17QG9mZ6005366; Thu, 26 Aug 2021 16:09:48 GMT (envelope-from git) Date: Thu, 26 Aug 2021 16:09:48 GMT Message-Id: <202108261609.17QG9mZ6005366@gitrepo.freebsd.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org From: Konstantin Belousov Subject: git: 7aa47cace149 - main - amd64: remove lfence after swapgs on syscall entry MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Git-Committer: kib X-Git-Repository: src X-Git-Refname: refs/heads/main X-Git-Reftype: branch X-Git-Commit: 7aa47cace14948a7b8277a4b24a0ca9e0308990a Auto-Submitted: auto-generated X-BeenThere: dev-commits-src-main@freebsd.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: Commit messages for the main branch of the src repository List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 26 Aug 2021 16:09:48 -0000 The branch main has been updated by kib: URL: https://cgit.FreeBSD.org/src/commit/?id=7aa47cace14948a7b8277a4b24a0ca9e0308990a commit 7aa47cace14948a7b8277a4b24a0ca9e0308990a Author: Konstantin Belousov AuthorDate: 2021-08-25 19:28:57 +0000 Commit: Konstantin Belousov CommitDate: 2021-08-26 16:09:21 +0000 amd64: remove lfence after swapgs on syscall entry According to the description of SBSS issue at https://software.intel.com/content/www/us/en/develop/articles/software-security-guidance/technical-documentation/speculative-behavior-swapgs-and-segment-registers.html lfence after swapgs is needed only for the case when swapgs could be speculatively executed. Since syscall entry, unlike exception and interrupt entries, executes swapgs unconditionally, there is no opportunity for speculation. Reviewed by: markj Sponsored by: The FreeBSD Foundation MFC after: 1 week Differential revision: https://reviews.freebsd.org/D31682 --- sys/amd64/amd64/exception.S | 2 -- 1 file changed, 2 deletions(-) diff --git a/sys/amd64/amd64/exception.S b/sys/amd64/amd64/exception.S index d1e49faa40e7..6471f9a3041c 100644 --- a/sys/amd64/amd64/exception.S +++ b/sys/amd64/amd64/exception.S @@ -524,7 +524,6 @@ prot_addrf: SUPERALIGN_TEXT IDTVEC(fast_syscall_pti) swapgs - lfence cmpq $~0,PCPU(UCR3) je fast_syscall_common movq %rax,PCPU(SCRATCH_RAX) @@ -535,7 +534,6 @@ IDTVEC(fast_syscall_pti) SUPERALIGN_TEXT IDTVEC(fast_syscall) swapgs - lfence fast_syscall_common: movq %rsp,PCPU(SCRATCH_RSP) movq PCPU(RSP0),%rsp