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=-19.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT autolearn=unavailable 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 77955C2B9F7 for ; Mon, 24 May 2021 16:00:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5C9CF6109F for ; Mon, 24 May 2021 16:00:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234625AbhEXQB5 (ORCPT ); Mon, 24 May 2021 12:01:57 -0400 Received: from mail.kernel.org ([198.145.29.99]:41186 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234427AbhEXPza (ORCPT ); Mon, 24 May 2021 11:55:30 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id B73CE61445; Mon, 24 May 2021 15:41:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1621870914; bh=6LlI/WolxupHlz9B/VtgcQD5lFbpjlG7zI70KKiUago=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=osuoNBunzhwcYPwjxxkWWvUxOyB1SMpF68jt5+ERgTj7SK7Sk0WMWYGYMzvWiiklj SVfc1ENZPTK28FtrusThtGVY+GwHc+TOLLTQFCa7vYtPISOJdP81rRFGFIAXASqO/i gf9rDkjmIihsHRWNnAK7a/KOcK62McMOwbyEurec= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Joerg Roedel , Borislav Petkov Subject: [PATCH 5.10 058/104] x86/sev-es: Use __put_user()/__get_user() for data accesses Date: Mon, 24 May 2021 17:25:53 +0200 Message-Id: <20210524152334.782450622@linuxfoundation.org> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20210524152332.844251980@linuxfoundation.org> References: <20210524152332.844251980@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Joerg Roedel commit 4954f5b8ef0baf70fe978d1a99a5f70e4dd5c877 upstream. The put_user() and get_user() functions do checks on the address which is passed to them. They check whether the address is actually a user-space address and whether its fine to access it. They also call might_fault() to indicate that they could fault and possibly sleep. All of these checks are neither wanted nor needed in the #VC exception handler, which can be invoked from almost any context and also for MMIO instructions from kernel space on kernel memory. All the #VC handler wants to know is whether a fault happened when the access was tried. This is provided by __put_user()/__get_user(), which just do the access no matter what. Also add comments explaining why __get_user() and __put_user() are the best choice here and why it is safe to use them in this context. Also explain why copy_to/from_user can't be used. In addition, also revert commit 7024f60d6552 ("x86/sev-es: Handle string port IO to kernel memory properly") because using __get_user()/__put_user() fixes the same problem while the above commit introduced several problems: 1) It uses access_ok() which is only allowed in task context. 2) It uses memcpy() which has no fault handling at all and is thus unsafe to use here. [ bp: Fix up commit ID of the reverted commit above. ] Fixes: f980f9c31a92 ("x86/sev-es: Compile early handler code into kernel image") Signed-off-by: Joerg Roedel Signed-off-by: Borislav Petkov Cc: stable@vger.kernel.org # v5.10+ Link: https://lkml.kernel.org/r/20210519135251.30093-4-joro@8bytes.org Signed-off-by: Greg Kroah-Hartman --- arch/x86/kernel/sev-es.c | 66 ++++++++++++++++++++++++++++++++--------------- 1 file changed, 46 insertions(+), 20 deletions(-) --- a/arch/x86/kernel/sev-es.c +++ b/arch/x86/kernel/sev-es.c @@ -288,31 +288,44 @@ static enum es_result vc_write_mem(struc u16 d2; u8 d1; - /* If instruction ran in kernel mode and the I/O buffer is in kernel space */ - if (!user_mode(ctxt->regs) && !access_ok(target, size)) { - memcpy(dst, buf, size); - return ES_OK; - } - + /* + * This function uses __put_user() independent of whether kernel or user + * memory is accessed. This works fine because __put_user() does no + * sanity checks of the pointer being accessed. All that it does is + * to report when the access failed. + * + * Also, this function runs in atomic context, so __put_user() is not + * allowed to sleep. The page-fault handler detects that it is running + * in atomic context and will not try to take mmap_sem and handle the + * fault, so additional pagefault_enable()/disable() calls are not + * needed. + * + * The access can't be done via copy_to_user() here because + * vc_write_mem() must not use string instructions to access unsafe + * memory. The reason is that MOVS is emulated by the #VC handler by + * splitting the move up into a read and a write and taking a nested #VC + * exception on whatever of them is the MMIO access. Using string + * instructions here would cause infinite nesting. + */ switch (size) { case 1: memcpy(&d1, buf, 1); - if (put_user(d1, target)) + if (__put_user(d1, target)) goto fault; break; case 2: memcpy(&d2, buf, 2); - if (put_user(d2, target)) + if (__put_user(d2, target)) goto fault; break; case 4: memcpy(&d4, buf, 4); - if (put_user(d4, target)) + if (__put_user(d4, target)) goto fault; break; case 8: memcpy(&d8, buf, 8); - if (put_user(d8, target)) + if (__put_user(d8, target)) goto fault; break; default: @@ -343,30 +356,43 @@ static enum es_result vc_read_mem(struct u16 d2; u8 d1; - /* If instruction ran in kernel mode and the I/O buffer is in kernel space */ - if (!user_mode(ctxt->regs) && !access_ok(s, size)) { - memcpy(buf, src, size); - return ES_OK; - } - + /* + * This function uses __get_user() independent of whether kernel or user + * memory is accessed. This works fine because __get_user() does no + * sanity checks of the pointer being accessed. All that it does is + * to report when the access failed. + * + * Also, this function runs in atomic context, so __get_user() is not + * allowed to sleep. The page-fault handler detects that it is running + * in atomic context and will not try to take mmap_sem and handle the + * fault, so additional pagefault_enable()/disable() calls are not + * needed. + * + * The access can't be done via copy_from_user() here because + * vc_read_mem() must not use string instructions to access unsafe + * memory. The reason is that MOVS is emulated by the #VC handler by + * splitting the move up into a read and a write and taking a nested #VC + * exception on whatever of them is the MMIO access. Using string + * instructions here would cause infinite nesting. + */ switch (size) { case 1: - if (get_user(d1, s)) + if (__get_user(d1, s)) goto fault; memcpy(buf, &d1, 1); break; case 2: - if (get_user(d2, s)) + if (__get_user(d2, s)) goto fault; memcpy(buf, &d2, 2); break; case 4: - if (get_user(d4, s)) + if (__get_user(d4, s)) goto fault; memcpy(buf, &d4, 4); break; case 8: - if (get_user(d8, s)) + if (__get_user(d8, s)) goto fault; memcpy(buf, &d8, 8); break;