From mboxrd@z Thu Jan 1 00:00:00 1970 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=-6.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS 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 9D335C433DF for ; Mon, 15 Jun 2020 12:59:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 70ADB2076A for ; Mon, 15 Jun 2020 12:59:48 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=notmuch.email header.i=@notmuch.email header.b="R8p8tQbJ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730122AbgFOM7r (ORCPT ); Mon, 15 Jun 2020 08:59:47 -0400 Received: from mx.h4ck.space ([159.69.146.50]:51238 "EHLO mx.h4ck.space" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730070AbgFOM7q (ORCPT ); Mon, 15 Jun 2020 08:59:46 -0400 Date: Mon, 15 Jun 2020 14:59:30 +0200 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=notmuch.email; s=mail; t=1592225982; bh=xEaHOZrOGFdQ2ZrwzvdfXydcdbqmR2TMLyGFVx8L8Mw=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=R8p8tQbJcszCLNq0puYi9G3zOC1OTfFpmli4OCFJxHtmYkHIyy1VoyYW9i8fZT7oB GuyGEBGJ1lHJVDTzSHjBnP/vOu3/w9QX3Ddy4INc43vtpkHiKbLyJLbd3QCbcViqs6 nr6kMJE2Ii23XuYntAEzjkkZ4adGqMwytc6hnejE= From: andi@notmuch.email To: Brendan Shanks Cc: linux-kernel@vger.kernel.org, ricardo.neri-calderon@linux.intel.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, x86@kernel.org, ebiederm@xmission.com, Babu.Moger@amd.com Subject: Re: [PATCH v4] x86/umip: Add emulation/spoofing for SLDT and STR instructions Message-ID: <20200615125930.qydseozyrzjjz42e@wrt> References: <20200609175423.31568-1-bshanks@codeweavers.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20200609175423.31568-1-bshanks@codeweavers.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10:54 09.06.20, Brendan Shanks wrote: > Add emulation/spoofing of SLDT and STR for both 32- and 64-bit > processes. > > Wine users have found a small number of Windows apps using SLDT that > were crashing when run on UMIP-enabled systems. > > Reported-by: Andreas Rammhold > Originally-by: Ricardo Neri > Signed-off-by: Brendan Shanks > --- > > v4: Use braces for every clause of the conditional. I tried a switch(), > but it takes more lines and looks more cluttered (especially with the > #ifdef). > Also replace out-of-date comment at top of file. > > arch/x86/kernel/umip.c | 38 ++++++++++++++++++++++++++------------ > 1 file changed, 26 insertions(+), 12 deletions(-) > > diff --git a/arch/x86/kernel/umip.c b/arch/x86/kernel/umip.c > index 8d5cbe1bbb3b..62f4f0afb979 100644 > --- a/arch/x86/kernel/umip.c > +++ b/arch/x86/kernel/umip.c > @@ -45,11 +45,12 @@ > * value that, lies close to the top of the kernel memory. The limit for the GDT > * and the IDT are set to zero. > * > - * Given that SLDT and STR are not commonly used in programs that run on WineHQ > - * or DOSEMU2, they are not emulated. > - * > * The instruction smsw is emulated to return the value that the register CR0 > * has at boot time as set in the head_32. > + * sldt and str are emulated to return the values that the kernel programmatically > + * assigns: > + * - sldt returns (GDT_ENTRY_LDT * 8) if an LDT has been set, 0 if not. > + * - str returns (GDT_ENTRY_TSS * 8). > * > * Emulation is provided for both 32-bit and 64-bit processes. > * > @@ -244,16 +245,34 @@ static int emulate_umip_insn(struct insn *insn, int umip_inst, > *data_size += UMIP_GDT_IDT_LIMIT_SIZE; > memcpy(data, &dummy_limit, UMIP_GDT_IDT_LIMIT_SIZE); > > - } else if (umip_inst == UMIP_INST_SMSW) { > - unsigned long dummy_value = CR0_STATE; > + } else if (umip_inst == UMIP_INST_SMSW || umip_inst == UMIP_INST_SLDT || > + umip_inst == UMIP_INST_STR) { > + unsigned long dummy_value; > + > + if (umip_inst == UMIP_INST_SMSW) { > + dummy_value = CR0_STATE; > + } else if (umip_inst == UMIP_INST_STR) { > + dummy_value = GDT_ENTRY_TSS * 8; > + } else if (umip_inst == UMIP_INST_SLDT) { > +#ifdef CONFIG_MODIFY_LDT_SYSCALL > + down_read(¤t->mm->context.ldt_usr_sem); > + if (current->mm->context.ldt) > + dummy_value = GDT_ENTRY_LDT * 8; > + else > + dummy_value = 0; > + up_read(¤t->mm->context.ldt_usr_sem); > +#else > + dummy_value = 0; > +#endif > + } > > /* > - * Even though the CR0 register has 4 bytes, the number > + * For these 3 instructions, the number > * of bytes to be copied in the result buffer is determined > * by whether the operand is a register or a memory location. > * If operand is a register, return as many bytes as the operand > * size. If operand is memory, return only the two least > - * siginificant bytes of CR0. > + * siginificant bytes. > */ > if (X86_MODRM_MOD(insn->modrm.value) == 3) > *data_size = insn->opnd_bytes; > @@ -261,7 +280,6 @@ static int emulate_umip_insn(struct insn *insn, int umip_inst, > *data_size = 2; > > memcpy(data, &dummy_value, *data_size); > - /* STR and SLDT are not emulated */ > } else { > return -EINVAL; > } > @@ -383,10 +401,6 @@ bool fixup_umip_exception(struct pt_regs *regs) > umip_pr_warn(regs, "%s instruction cannot be used by applications.\n", > umip_insns[umip_inst]); > > - /* Do not emulate (spoof) SLDT or STR. */ > - if (umip_inst == UMIP_INST_STR || umip_inst == UMIP_INST_SLDT) > - return false; > - > umip_pr_warn(regs, "For now, expensive software emulation returns the result.\n"); > > if (emulate_umip_insn(&insn, umip_inst, dummy_data, &dummy_data_size, > -- > 2.26.2 > A bit late but I was able to test my workload with the above patch applied on 5.7.2. Tested-by: Andreas Rammhold