From patchwork Thu Jan 10 21:09:45 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Khalid Aziz X-Patchwork-Id: 10756945 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id BC335159A for ; Thu, 10 Jan 2019 21:13:04 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id A9EB329BCC for ; Thu, 10 Jan 2019 21:13:04 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 99FAE29BE7; Thu, 10 Jan 2019 21:13:04 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.3 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,RCVD_IN_DNSWL_MED autolearn=ham version=3.3.1 Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.wl.linuxfoundation.org (Postfix) with SMTP id A46C129BCC for ; Thu, 10 Jan 2019 21:13:03 +0000 (UTC) Received: (qmail 15454 invoked by uid 550); 10 Jan 2019 21:11:26 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Delivered-To: mailing list kernel-hardening@lists.openwall.com Received: (qmail 15395 invoked from network); 10 Jan 2019 21:11:24 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=from : to : cc : subject : date : message-id : in-reply-to : references : in-reply-to : references; s=corp-2018-07-02; bh=UbctwoSk8tN3IcjUiRawhNiiTGCYFxkfE1vdJR34/p4=; b=pXlQwsE6eT5Gwd80itwTVz5RN+Ix5BpvxJmBfde1uZygV+Rslofe7x724kOLvkrhuoDm VaufXFJc0x/bhg4csb86xgTa5oRsgGXNUwpk6jBaSYVCOK08HIMLKrRQFFXQuF/ljQLa c9M5nGEttCW3mctUWC2vYB1gn4wLmkHIUFEx/Aw1I+7qiQ3knEVUexcfa2bolqzEyvV3 LmtzvRDDdYXn9ZOKH/gctHRPShqvLWBf/rOrAA8BIVQSKsMuP44bA/KoMe+nCz6XDCkg Fj6Mqgg33kI6zR9S0fSK8spVh3Dy3zDN5Jmnk4/mwptg9ykfT++lnvDkaEVHNpTf9Xm8 jw== From: Khalid Aziz To: juergh@gmail.com, tycho@tycho.ws, jsteckli@amazon.de, ak@linux.intel.com, torvalds@linux-foundation.org, liran.alon@oracle.com, keescook@google.com, konrad.wilk@oracle.com Cc: deepa.srinivasan@oracle.com, chris.hyser@oracle.com, tyhicks@canonical.com, dwmw@amazon.co.uk, andrew.cooper3@citrix.com, jcm@redhat.com, boris.ostrovsky@oracle.com, kanth.ghatraju@oracle.com, joao.m.martins@oracle.com, jmattson@google.com, pradeep.vincent@oracle.com, john.haxby@oracle.com, tglx@linutronix.de, kirill.shutemov@linux.intel.com, hch@lst.de, steven.sistare@oracle.com, kernel-hardening@lists.openwall.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, x86@kernel.org, "Vasileios P . Kemerlis" , Juerg Haefliger , Tycho Andersen , Marco Benatto , David Woodhouse , Khalid Aziz Subject: [RFC PATCH v7 13/16] xpfo, mm: optimize spinlock usage in xpfo_kunmap Date: Thu, 10 Jan 2019 14:09:45 -0700 Message-Id: <95b6fa40ce6c7afb4a9e58f8d747d86aa7a94177.1547153058.git.khalid.aziz@oracle.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: References: In-Reply-To: References: X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=9132 signatures=668680 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=822 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1901100164 X-Virus-Scanned: ClamAV using ClamSMTP From: Julian Stecklina Only the xpfo_kunmap call that needs to actually unmap the page needs to be serialized. We need to be careful to handle the case, where after the atomic decrement of the mapcount, a xpfo_kmap increased the mapcount again. In this case, we can safely skip modifying the page table. Model-checked with up to 4 concurrent callers with Spin. Signed-off-by: Julian Stecklina Cc: x86@kernel.org Cc: kernel-hardening@lists.openwall.com Cc: Vasileios P. Kemerlis Cc: Juerg Haefliger Cc: Tycho Andersen Cc: Marco Benatto Cc: David Woodhouse Signed-off-by: Khalid Aziz --- mm/xpfo.c | 22 ++++++++++++---------- 1 file changed, 12 insertions(+), 10 deletions(-) diff --git a/mm/xpfo.c b/mm/xpfo.c index cbfeafc2f10f..dbf20efb0499 100644 --- a/mm/xpfo.c +++ b/mm/xpfo.c @@ -149,22 +149,24 @@ void xpfo_kunmap(void *kaddr, struct page *page) if (!PageXpfoUser(page)) return; - spin_lock(&page->xpfo_lock); - /* * The page is to be allocated back to user space, so unmap it from the * kernel, flush the TLB and tag it as a user page. */ if (atomic_dec_return(&page->xpfo_mapcount) == 0) { -#ifdef CONFIG_XPFO_DEBUG - BUG_ON(PageXpfoUnmapped(page)); -#endif - SetPageXpfoUnmapped(page); - set_kpte(kaddr, page, __pgprot(0)); - xpfo_cond_flush_kernel_tlb(page, 0); - } + spin_lock(&page->xpfo_lock); - spin_unlock(&page->xpfo_lock); + /* + * In the case, where we raced with kmap after the + * atomic_dec_return, we must not nuke the mapping. + */ + if (atomic_read(&page->xpfo_mapcount) == 0) { + SetPageXpfoUnmapped(page); + set_kpte(kaddr, page, __pgprot(0)); + xpfo_cond_flush_kernel_tlb(page, 0); + } + spin_unlock(&page->xpfo_lock); + } } EXPORT_SYMBOL(xpfo_kunmap);