From nobody Wed Apr 8 14:04:12 2026 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 C2D6CC38A2D for ; Wed, 26 Oct 2022 21:59:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233542AbiJZV7R (ORCPT ); Wed, 26 Oct 2022 17:59:17 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55300 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229592AbiJZV7P (ORCPT ); Wed, 26 Oct 2022 17:59:15 -0400 X-Greylist: delayed 345 seconds by postgrey-1.37 at lindbergh.monkeyblade.net; Wed, 26 Oct 2022 14:59:13 PDT Received: from cae.in-ulm.de (cae.in-ulm.de [217.10.14.231]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 54C6A7CABD; Wed, 26 Oct 2022 14:59:13 -0700 (PDT) Received: by cae.in-ulm.de (Postfix, from userid 1000) id 8C92A140306; Wed, 26 Oct 2022 23:53:26 +0200 (CEST) From: "Christian A. Ehrhardt" To: Sean Christopherson Cc: "Christian A. Ehrhardt" , Paolo Bonzini , Kees Cook , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] x86/kvm: Fix state restore in em_rsm Date: Wed, 26 Oct 2022 23:52:54 +0200 Message-Id: <20221026215255.1063662-1-lk@c--e.de> X-Mailer: git-send-email 2.30.2 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Syzkaller reports a stack-out-of-bounds access when emulating RSM (return from system management mode). Assume that a 64-bit capable host (i.e. CONFIG_X86_64 is true) emulates a guest cpu that does not support 64-bit mode. In this case RSM must use the 32-bit version of the SMM state map which only contains space for 8 general purpose registers. However, NR_EMULATOR_GPRS is defined to 16 due to CONFIG_X86_64. As a result rsm_load_state_32 will try to restore 16 registers from the state save area which only contains 8 registers. Manual offset calculation easily shows that memory beyond the end of the smstate buffer is accessed in this case. Revert the relevant parts of b443183a25ab and use explicit constants for the number of general purpose registers, again. This also ensures that the code in rsm_load_state_{32,64} matches what is done in enter_smm_save_state_{32,64}. Fixes: b443183a25ab ("KVM: x86: Reduce the number of emulator GPRs to '8' f= or 32-bit KVM") Signed-off-by: Christian A. Ehrhardt --- arch/x86/kvm/emulate.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c index 3b27622d4642..05355ebaf4f3 100644 --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -2432,7 +2432,7 @@ static int rsm_load_state_32(struct x86_emulate_ctxt = *ctxt, ctxt->eflags =3D GET_SMSTATE(u32, smstate, 0x7ff4) | X86_EFLA= GS_FIXED; ctxt->_eip =3D GET_SMSTATE(u32, smstate, 0x7ff0); =20 - for (i =3D 0; i < NR_EMULATOR_GPRS; i++) + for (i =3D 0; i < 8; i++) *reg_write(ctxt, i) =3D GET_SMSTATE(u32, smstate, 0x7fd0 + i * 4); =20 val =3D GET_SMSTATE(u32, smstate, 0x7fcc); @@ -2489,7 +2489,7 @@ static int rsm_load_state_64(struct x86_emulate_ctxt = *ctxt, u16 selector; int i, r; =20 - for (i =3D 0; i < NR_EMULATOR_GPRS; i++) + for (i =3D 0; i < 16; i++) *reg_write(ctxt, i) =3D GET_SMSTATE(u64, smstate, 0x7ff8 - i * 8); =20 ctxt->_eip =3D GET_SMSTATE(u64, smstate, 0x7f78); --=20 2.34.1