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=-3.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_PASS,T_DKIMWL_WL_HIGH,USER_AGENT_GIT 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 44C56C43334 for ; Mon, 3 Sep 2018 22:59:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F20A82086C for ; Mon, 3 Sep 2018 22:59:48 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="IKUxFcYJ" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org F20A82086C Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727164AbeIDDWF (ORCPT ); Mon, 3 Sep 2018 23:22:05 -0400 Received: from mail.kernel.org ([198.145.29.99]:32816 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726133AbeIDDWE (ORCPT ); Mon, 3 Sep 2018 23:22:04 -0400 Received: from localhost (c-71-202-137-17.hsd1.ca.comcast.net [71.202.137.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id B94BE2086B; Mon, 3 Sep 2018 22:59:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1536015585; bh=yiuM0LmMCNa0Zcfc0pDNNpkzNuU0GVpMUTBN14M5TKo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:In-Reply-To: References:From; b=IKUxFcYJYBvAyKK/ETpaPjJXsl2ErCfLAwhtvdkGkgro1cMqFbt7oRLtV4QKDAhYx atl0adewsHN35xslC8UBKX6NVZN0SiTJMVNGYyDkk/jWgQPN5IT7usilKX3vi6UJNN TsdJJsR34hJjfrP+2haDxa7+LC5WjjYSgSgIWB3U= From: Andy Lutomirski To: x86@kernel.org Cc: Borislav Petkov , LKML , Dave Hansen , Adrian Hunter , Alexander Shishkin , Arnaldo Carvalho de Melo , Linus Torvalds , Josh Poimboeuf , Joerg Roedel , Jiri Olsa , Andi Kleen , Peter Zijlstra , Andy Lutomirski Subject: [PATCH v2 1/3] x86/entry/64: Document idtentry Date: Mon, 3 Sep 2018 15:59:42 -0700 Message-Id: <6e56c3ad94879e41afe345750bc28ccc0e820ea8.1536015544.git.luto@kernel.org> X-Mailer: git-send-email 2.17.1 In-Reply-To: References: In-Reply-To: References: Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The idtentry macro is complicated and magical. Document what it does to help future readers and to allow future patches to adjust the code and docs at the same time. Signed-off-by: Andy Lutomirski --- arch/x86/entry/entry_64.S | 35 +++++++++++++++++++++++++++++++++++ arch/x86/kernel/traps.c | 4 ++++ 2 files changed, 39 insertions(+) diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index 957dfb693ecc..1796c42e08af 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -900,6 +900,41 @@ apicinterrupt IRQ_WORK_VECTOR irq_work_interrupt smp_irq_work_interrupt */ #define CPU_TSS_IST(x) PER_CPU_VAR(cpu_tss_rw) + (TSS_ist + ((x) - 1) * 8) +/** + * idtentry - Generate an IDT entry stub + * @sym: Name of the generated entry point + * @do_sym: C function to be called + * @has_error_code: True if this IDT vector has an error code on the stack + * @paranoid: non-zero means that this vector may be invoked from kernel + * mode with user GSBASE and/or user CR3. 2 is special -- see below. + * @shift_ist: Set to an IST index if entries from kernel mode should + * decrement the IST stack so that nested entries get a fresh + * stack. (This is for #DB, which has a nasty habit of + * recursing.) + * + * idtentry generates an IDT stub that sets up a usable kernel context, + * creates struct pt_regs, and calls @do_sym. The stub has the following + * special behaviors: + * + * On an entry from user mode, the stub switches from the trampoline or + * IST stack to the normal thread stack. On an exit to user mode, the + * normal exit-to-usermode path is invoked. + * + * On an exit to kernel mode, if paranoid == 0, we check for preemption, + * whereas we omit the preemption check if @paranoid != 0. This is purely + * because the implementation is simpler this way. The kernel only needs + * to check for asynchronous kernel preemption when IRQ handlers return. + * + * If @paranoid == 0, then the stub will handle IRET faults by pretending + * that the fault came from user mode. It will handle gs_change faults by + * pretending that the fault happened with kernel GSBASE. Since this handling + * is omitted for @paranoid != 0, the #GP, #SS, and #NP stubs must have + * @paranoid == 0. This special handling will do the wrong thing for + * espfix-induced #DF on IRET, so #DF must not use @paranoid == 0. + * + * @paranoid == 2 is special: the stub will never switch stacks. This is for + * #DF: if the thread stack is somehow unusable, we'll still get a useful OOPS. + */ .macro idtentry sym do_sym has_error_code:req paranoid=0 shift_ist=-1 ENTRY(\sym) UNWIND_HINT_IRET_REGS offset=\has_error_code*8 diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index e6db475164ed..1a90821c0b74 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -383,6 +383,10 @@ dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code) * we won't enable interupts or schedule before we invoke * general_protection, so nothing will clobber the stack * frame we just set up. + * + * We will enter general_protection with kernel GSBASE, + * which is what the stub expects, given that the faulting + * RIP will be the IRET instruction. */ regs->ip = (unsigned long)general_protection; regs->sp = (unsigned long)&gpregs->orig_ax; -- 2.17.1