From patchwork Thu Jan 28 12:58:23 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jarkko Sakkinen X-Patchwork-Id: 12053633 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=-19.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 8D143C4332D for ; Thu, 28 Jan 2021 12:59:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6552764DE4 for ; Thu, 28 Jan 2021 12:59:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231882AbhA1M7N (ORCPT ); Thu, 28 Jan 2021 07:59:13 -0500 Received: from mail.kernel.org ([198.145.29.99]:60172 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231880AbhA1M7K (ORCPT ); Thu, 28 Jan 2021 07:59:10 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 2B15764DD8; Thu, 28 Jan 2021 12:58:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1611838709; bh=+X6/S8TIzROyCscNL2Zpna/HXn70q3+ajUjZ7HNRiAU=; h=From:To:Cc:Subject:Date:From; b=RGWcjlLIWrGovksSstY30JmqTRfZCBscviaxR4kslvyFkhO8bCAtHDB2WUjsYZzcv MutNhdGi36yfC/dc4S28cWOtdWPd37n2sW8o/oFY9mvvUBDHGwmql7zRm2vOf0hwdk Nkf2K9jItce47ytcpxq0QWGqcn9i9QsiPjv5Ha7+Qil6wiUnlER3rY+fUdLiGxizhg a2f/urXpywgTwFsHm++rY6YjbyNYOHXN3269HrLtqI6jYhtGcsKfPS7gXW5nft/iqO RRLZHsYkfZr9Gfev44tEmL2xdoL7Vwd9bVvPkHdwet9nmSJtoTE3GNELBQCyh+XBF6 nuebD84od3Zyw== From: Jarkko Sakkinen To: linux-sgx@vger.kernel.org Cc: dave.hansen@intel.com, Jarkko Sakkinen , stable@vger.kernel.org, Sean Christopherson , Haitao Huang , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H. Peter Anvin" , Jethro Beekman , linux-kernel@vger.kernel.org Subject: [PATCH v5] x86/sgx: Fix use-after-free in sgx_mmu_notifier_release() Date: Thu, 28 Jan 2021 14:58:23 +0200 Message-Id: <20210128125823.18660-1-jarkko@kernel.org> X-Mailer: git-send-email 2.30.0 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-sgx@vger.kernel.org The most trivial example of a race condition can be demonstrated by this sequence where mm_list contains just one entry: CPU A CPU B -> sgx_release() -> sgx_mmu_notifier_release() -> list_del_rcu() <- list_del_rcu() -> kref_put() -> sgx_encl_release() -> synchronize_srcu() -> cleanup_srcu_struct() A sequence similar to this has also been spotted in tests under high stress: [ +0.000008] WARNING: CPU: 3 PID: 7620 at kernel/rcu/srcutree.c:374 cleanup_srcu_struct+0xed/0x100 Albeit not spotted in the tests, it's also entirely possible that the following scenario could happen: CPU A CPU B -> sgx_release() -> sgx_mmu_notifier_release() -> list_del_rcu() -> kref_put() -> sgx_encl_release() -> cleanup_srcu_struct() <- cleanup_srcu_struct() -> synchronize_srcu() This scenario would lead into use-after free in cleaup_srcu_struct(). Fix this by taking a reference to the enclave in sgx_mmu_notifier_release(). Cc: stable@vger.kernel.org Fixes: 1728ab54b4be ("x86/sgx: Add a page reclaimer") Suggested-by: Sean Christopherson Reported-by: Haitao Huang Signed-off-by: Jarkko Sakkinen --- v5: - To make sure that the instance does not get deleted use kref_get() kref_put(). This also removes the need for additional synchronize_srcu(). v4: - Rewrite the commit message. - Just change the call order. *_expedited() is out of scope for this bug fix. v3: Fine-tuned tags, and added missing change log for v2. v2: Switch to synchronize_srcu_expedited(). arch/x86/kernel/cpu/sgx/encl.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c index ee50a5010277..5ecbcf94ec2a 100644 --- a/arch/x86/kernel/cpu/sgx/encl.c +++ b/arch/x86/kernel/cpu/sgx/encl.c @@ -465,6 +465,7 @@ static void sgx_mmu_notifier_release(struct mmu_notifier *mn, spin_lock(&encl_mm->encl->mm_lock); list_for_each_entry(tmp, &encl_mm->encl->mm_list, list) { if (tmp == encl_mm) { + kref_get(&encl_mm->encl->refcount); list_del_rcu(&encl_mm->list); break; } @@ -474,6 +475,7 @@ static void sgx_mmu_notifier_release(struct mmu_notifier *mn, if (tmp == encl_mm) { synchronize_srcu(&encl_mm->encl->srcu); mmu_notifier_put(mn); + kref_put(&encl_mm->encl->refcount, sgx_encl_release); } }