From patchwork Tue Jan 26 16:31:05 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jan Beulich X-Patchwork-Id: 12047363 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-17.2 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id AB569C433E0 for ; Tue, 26 Jan 2021 16:31:23 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 6A94722210 for ; Tue, 26 Jan 2021 16:31:23 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6A94722210 Authentication-Results: mail.kernel.org; dmarc=fail (p=quarantine dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from list by lists.xenproject.org with outflank-mailman.75286.135507 (Exim 4.92) (envelope-from ) id 1l4RFD-0005OD-Dc; Tue, 26 Jan 2021 16:31:07 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 75286.135507; Tue, 26 Jan 2021 16:31:07 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1l4RFD-0005O6-9f; Tue, 26 Jan 2021 16:31:07 +0000 Received: by outflank-mailman (input) for mailman id 75286; Tue, 26 Jan 2021 16:31:06 +0000 Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1l4RFC-0005O1-4r for xen-devel@lists.xenproject.org; Tue, 26 Jan 2021 16:31:06 +0000 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id 7afe156b-443b-4a4e-aaf7-218be25d5f7b; Tue, 26 Jan 2021 16:31:05 +0000 (UTC) Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 7459FB71F; Tue, 26 Jan 2021 16:31:04 +0000 (UTC) X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: 7afe156b-443b-4a4e-aaf7-218be25d5f7b X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1611678664; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=glkROfFJIVPSt4bFvVUxxsyDy6gtPVilRE3ZV2UKq8U=; b=l49GIzjuOMZndfRKLO/hD79+E8Kr6EGdUVQJT+TNVv1/9GxeTI0kiS0T5WnJsc77ZS2RDG mg2HTUmoQjhPFSsQT/N+eU/mmWoasFqy986lYoteYTQex9yvE3oZPhnnIPTQk5rP7Xsi+r S7Q2EI28q0XGEoQpA33xTNldaRm9ZMs= To: "xen-devel@lists.xenproject.org" Cc: Andrew Cooper , Wei Liu , =?utf-8?q?Roger_Pau_Monn=C3=A9?= From: Jan Beulich Subject: [PATCH] x86/PV: use 64-bit subtract to adjust guest RIP upon missing SYSCALL callbacks Message-ID: <29c38fa2-8337-0566-2053-ddcaf88ed01d@suse.com> Date: Tue, 26 Jan 2021 17:31:05 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.1 MIME-Version: 1.0 Content-Language: en-US When discussing the shrunk down version of the commit in question it was said (in reply to my conditional choosing of the width): "However, the 32bit case isn't actually interesting here. A guest can't execute a SYSCALL instruction on/across the 4G->0 boundary because the M2P is mapped NX up to the 4G boundary, so we can never reach this point with %eip < 2. Therefore, the 64bit-only form is the appropriate one to use, which solves any question of cleverness, or potential decode stalls it causes." Fixes: ca6fcf4321b3 ("x86/pv: Inject #UD for missing SYSCALL callbacks") Signed-off-by: Jan Beulich Reviewed-by: Andrew Cooper --- a/xen/arch/x86/x86_64/entry.S +++ b/xen/arch/x86/x86_64/entry.S @@ -42,7 +42,7 @@ ENTRY(switch_to_kernel) UNLIKELY_START(z, syscall_no_callback) /* TB_eip == 0 => #UD */ mov VCPU_trap_ctxt(%rbx), %rdi movl $X86_EXC_UD, UREGS_entry_vector(%rsp) - subl $2, UREGS_rip(%rsp) + subq $2, UREGS_rip(%rsp) mov X86_EXC_UD * TRAPINFO_sizeof + TRAPINFO_eip(%rdi), %rax testb $4, X86_EXC_UD * TRAPINFO_sizeof + TRAPINFO_flags(%rdi) setnz %cl