From patchwork Tue Feb 8 09:34:04 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Hou Wenlong X-Patchwork-Id: 12738407 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 96408C433FE for ; Tue, 8 Feb 2022 09:34:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1355394AbiBHJeQ (ORCPT ); Tue, 8 Feb 2022 04:34:16 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41890 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1355334AbiBHJeO (ORCPT ); Tue, 8 Feb 2022 04:34:14 -0500 Received: from out0-144.mail.aliyun.com (out0-144.mail.aliyun.com [140.205.0.144]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7CD32C03FEC9; Tue, 8 Feb 2022 01:34:13 -0800 (PST) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R111e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018047206;MF=houwenlong.hwl@antgroup.com;NM=1;PH=DS;RN=14;SR=0;TI=SMTPD_---.Mn034LU_1644312848; Received: from localhost(mailfrom:houwenlong.hwl@antgroup.com fp:SMTPD_---.Mn034LU_1644312848) by smtp.aliyun-inc.com(127.0.0.1); Tue, 08 Feb 2022 17:34:08 +0800 From: "Hou Wenlong" To: kvm@vger.kernel.org Cc: Sean Christopherson , Paolo Bonzini , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , linux-kernel@vger.kernel.org Subject: [PATCH v2 2/3] KVM: x86/emulator: Fix wrong privilege check for code segment in __load_segment_descriptor() Date: Tue, 08 Feb 2022 17:34:04 +0800 Message-Id: X-Mailer: git-send-email 2.31.1 In-Reply-To: References: MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Code segment descriptor can be loaded by jmp/call/ret, iret and int. The privilege checks are different between those instructions above realmode. Although, the emulator has use x86_transfer_type enumerate to differentiate them, but it is not really used in __load_segment_descriptor(). Note, far jump/call to call gate, task gate or task state segment are not implemented in emulator. As for far jump/call to code segment, if DPL > CPL for conforming code or (RPL > CPL or DPL != CPL) for non-conforming code, it should trigger #GP. The current checks are ok. As for far return, if RPL < CPL or DPL > RPL for conforming code or DPL != RPL for non-conforming code, it should trigger #GP. Outer level return is not implemented above virtual-8086 mode in emulator. So it implies that RPL <= CPL, but the current checks wouldn't trigger #GP if RPL < CPL. As for code segment loading in task switch, if DPL > RPL for conforming code or DPL != RPL for non-conforming code, it should trigger #TS. Since segment selector is loaded before segment descriptor when load state from tss, it implies that RPL = CPL, so the current checks are ok. The only problem in current implementation is missing RPL < CPL check for far return. However, change code to follow the manual is better. Reviewed-by: Sean Christopherson Signed-off-by: Hou Wenlong --- arch/x86/kvm/emulate.c | 31 +++++++++++++++++++++++-------- 1 file changed, 23 insertions(+), 8 deletions(-) -- 2.31.1 diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c index b7ee7de9f8cd..37c4213bdcc1 100644 --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -1631,14 +1631,29 @@ static int __load_segment_descriptor(struct x86_emulate_ctxt *ctxt, if (!(seg_desc.type & 8)) goto exception; - if (seg_desc.type & 4) { - /* conforming */ - if (dpl > cpl) - goto exception; - } else { - /* nonconforming */ - if (rpl > cpl || dpl != cpl) - goto exception; + /* RET can never return to an inner privilege level. */ + if (transfer == X86_TRANSFER_RET && rpl < cpl) + goto exception; + if (transfer == X86_TRANSFER_RET || transfer == X86_TRANSFER_TASK_SWITCH) { + if (seg_desc.type & 4) { + /* conforming */ + if (dpl > rpl) + goto exception; + } else { + /* nonconforming */ + if (dpl != rpl) + goto exception; + } + } else { /* X86_TRANSFER_CALL_JMP */ + if (seg_desc.type & 4) { + /* conforming */ + if (dpl > cpl) + goto exception; + } else { + /* nonconforming */ + if (rpl > cpl || dpl != cpl) + goto exception; + } } /* in long-mode d/b must be clear if l is set */ if (seg_desc.d && seg_desc.l) {