From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.11]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 854D048CFC; Wed, 15 May 2024 21:59:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.175.65.11 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1715810363; cv=none; b=O1L8EG5ZZdPzp2BaMTZARH975FYEY/jraqs0xo0PCQMPIt+gcxBcyJY48HFBKtrTnNtdPfJ9igp6Yzgh/fkrFPD6u8Wo6lc9YMtxWPZgtvxXarX6DJJUWReh1XHzCd/bqSEl1boOqK9O0wKx3xcZBJDu5dozvyg2lvAlzMdFvL8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1715810363; c=relaxed/simple; bh=xwvsZL4xUOasLuqkQ5VnMErfdvO4hSnbY9rPdgYHnw8=; h=Content-Type:To:Cc:Subject:References:Date:MIME-Version:From: Message-ID:In-Reply-To; b=UdaWrhdj/61FsK4O2RuJjIC77HUmt1XADy8YZJeP3UClZrBJT/9Ji9dPhi3rgCSwVmuhHq2GTR8Qa79XGM+bObSLqjTuhKowMbad8XCCM/vPPTZIG0H3KlmtD37q7SCvnq5RIFYfuppSbLC4BKUFxZ+FKLmAmjaULi88tg5+Wk0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com; spf=none smtp.mailfrom=linux.intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=Sagz+ON9; arc=none smtp.client-ip=198.175.65.11 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="Sagz+ON9" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1715810362; x=1747346362; h=to:cc:subject:references:date:mime-version: content-transfer-encoding:from:message-id:in-reply-to; bh=xwvsZL4xUOasLuqkQ5VnMErfdvO4hSnbY9rPdgYHnw8=; b=Sagz+ON96Zj72XFK3dbjyyE8kYm0CzZBlIW67c1aH+XKAkjUtJSMxb80 uN1IOhWjjmurY/2T7gftjJubBMiUHAVa3YNATHwanDvYlD4SC644X1YXk ugm9opIcRXTsrAyl3kMzOd1pMKcsPrlbxDxkcYah/8ARBsW5j6G/IzJ1Y 7zcGczMFCXDwrNUSd6cTQ01OA8t0fHFGv+vK+cChAZ1U6bIKdbpw3lVat 6RnG2ORtE3r5nqLA4t+gEgUL2k693yyhDzmXs4hp8m7Z3Gb9U36C0Emw8 ayYJVjD30DStjdT7y3TLnaj5A9lgrIwwncMv2oaAkW0ibHvMCwkS/TR32 g==; X-CSE-ConnectionGUID: 0I6/wIEdT52c1HZdLp4JpA== X-CSE-MsgGUID: pTpVoTB+S7eDLzucn0Fqmg== X-IronPort-AV: E=McAfee;i="6600,9927,11074"; a="22470042" X-IronPort-AV: E=Sophos;i="6.08,162,1712646000"; d="scan'208";a="22470042" Received: from orviesa001.jf.intel.com ([10.64.159.141]) by orvoesa103.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 May 2024 14:59:21 -0700 X-CSE-ConnectionGUID: 2xWY3NV1Sw2lwqC/3ruNtQ== X-CSE-MsgGUID: VrQJLRHBRIWE+xSyG5JefQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.08,162,1712646000"; d="scan'208";a="68654177" Received: from hhuan26-mobl.amr.corp.intel.com ([10.92.17.168]) by smtpauth.intel.com with ESMTP/TLS/AES256-SHA; 15 May 2024 14:59:20 -0700 Content-Type: text/plain; charset=iso-8859-15; format=flowed; delsp=yes To: dave.hansen@linux.intel.com, jarkko@kernel.org, kai.huang@intel.com, reinette.chatre@intel.com, linux-sgx@vger.kernel.org, linux-kernel@vger.kernel.org, "Dmitrii Kuvaiskii" Cc: mona.vij@intel.com, kailun.qin@intel.com, stable@vger.kernel.org Subject: Re: [PATCH v2 2/2] x86/sgx: Resolve EREMOVE page vs EAUG page data race References: <20240515131240.1304824-1-dmitrii.kuvaiskii@intel.com> <20240515131240.1304824-3-dmitrii.kuvaiskii@intel.com> Date: Wed, 15 May 2024 16:59:18 -0500 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 7bit From: "Haitao Huang" Organization: Intel Message-ID: In-Reply-To: <20240515131240.1304824-3-dmitrii.kuvaiskii@intel.com> User-Agent: Opera Mail/1.0 (Win32) On Wed, 15 May 2024 08:12:40 -0500, Dmitrii Kuvaiskii wrote: > Two enclave threads may try to add and remove the same enclave page > simultaneously (e.g., if the SGX runtime supports both lazy allocation > and MADV_DONTNEED semantics). Consider some enclave page added to the > enclave. User space decides to temporarily remove this page (e.g., > emulating the MADV_DONTNEED semantics) on CPU1. At the same time, user > space performs a memory access on the same page on CPU2, which results > in a #PF and ultimately in sgx_vma_fault(). Scenario proceeds as > follows: > > /* > * CPU1: User space performs > * ioctl(SGX_IOC_ENCLAVE_REMOVE_PAGES) > * on enclave page X > */ > sgx_encl_remove_pages() { > > mutex_lock(&encl->lock); > > entry = sgx_encl_load_page(encl); > /* > * verify that page is > * trimmed and accepted > */ > > mutex_unlock(&encl->lock); > > /* > * remove PTE entry; cannot > * be performed under lock > */ > sgx_zap_enclave_ptes(encl); > /* > * Fault on CPU2 on same page X > */ > sgx_vma_fault() { > /* > * PTE entry was removed, but the > * page is still in enclave's xarray > */ > xa_load(&encl->page_array) != NULL -> > /* > * SGX driver thinks that this page > * was swapped out and loads it > */ > mutex_lock(&encl->lock); > /* > * this is effectively a no-op > */ > entry = sgx_encl_load_page_in_vma(); > /* > * add PTE entry > * > * *BUG*: a PTE is installed for a > * page in process of being removed > */ > vmf_insert_pfn(...); > > mutex_unlock(&encl->lock); > return VM_FAULT_NOPAGE; > } > /* > * continue with page removal > */ > mutex_lock(&encl->lock); > > sgx_encl_free_epc_page(epc_page) { > /* > * remove page via EREMOVE > */ > /* > * free EPC page > */ > sgx_free_epc_page(epc_page); > } > > xa_erase(&encl->page_array); > > mutex_unlock(&encl->lock); > } > > Here, CPU1 removed the page. However CPU2 installed the PTE entry on the > same page. This enclave page becomes perpetually inaccessible (until > another SGX_IOC_ENCLAVE_REMOVE_PAGES ioctl). This is because the page is > marked accessible in the PTE entry but is not EAUGed, and any subsequent > access to this page raises a fault: with the kernel believing there to > be a valid VMA, the unlikely error code X86_PF_SGX encountered by code > path do_user_addr_fault() -> access_error() causes the SGX driver's > sgx_vma_fault() to be skipped and user space receives a SIGSEGV instead. > The userspace SIGSEGV handler cannot perform EACCEPT because the page > was not EAUGed. Thus, the user space is stuck with the inaccessible > page. > > Fix this race by forcing the fault handler on CPU2 to back off if the > page is currently being removed (on CPU1). This is achieved by > introducing a new flag SGX_ENCL_PAGE_BEING_REMOVED, which is unset by > default and set only right-before the first mutex_unlock() in > sgx_encl_remove_pages(). Upon loading the page, CPU2 checks whether this > page is being removed, and if yes then CPU2 backs off and waits until > the page is completely removed. After that, any memory access to this > page results in a normal "allocate and EAUG a page on #PF" flow. > > Fixes: 9849bb27152c ("x86/sgx: Support complete page removal") > Cc: stable@vger.kernel.org > Signed-off-by: Dmitrii Kuvaiskii > --- > arch/x86/kernel/cpu/sgx/encl.c | 3 ++- > arch/x86/kernel/cpu/sgx/encl.h | 3 +++ > arch/x86/kernel/cpu/sgx/ioctl.c | 1 + > 3 files changed, 6 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kernel/cpu/sgx/encl.c > b/arch/x86/kernel/cpu/sgx/encl.c > index 41f14b1a3025..7ccd8b2fce5f 100644 > --- a/arch/x86/kernel/cpu/sgx/encl.c > +++ b/arch/x86/kernel/cpu/sgx/encl.c > @@ -257,7 +257,8 @@ static struct sgx_encl_page > *__sgx_encl_load_page(struct sgx_encl *encl, > /* Entry successfully located. */ > if (entry->epc_page) { > - if (entry->desc & SGX_ENCL_PAGE_BEING_RECLAIMED) > + if (entry->desc & (SGX_ENCL_PAGE_BEING_RECLAIMED | > + SGX_ENCL_PAGE_BEING_REMOVED)) > return ERR_PTR(-EBUSY); > return entry; > diff --git a/arch/x86/kernel/cpu/sgx/encl.h > b/arch/x86/kernel/cpu/sgx/encl.h > index f94ff14c9486..fff5f2293ae7 100644 > --- a/arch/x86/kernel/cpu/sgx/encl.h > +++ b/arch/x86/kernel/cpu/sgx/encl.h > @@ -25,6 +25,9 @@ > /* 'desc' bit marking that the page is being reclaimed. */ > #define SGX_ENCL_PAGE_BEING_RECLAIMED BIT(3) > +/* 'desc' bit marking that the page is being removed. */ > +#define SGX_ENCL_PAGE_BEING_REMOVED BIT(2) > + > struct sgx_encl_page { > unsigned long desc; > unsigned long vm_max_prot_bits:8; > diff --git a/arch/x86/kernel/cpu/sgx/ioctl.c > b/arch/x86/kernel/cpu/sgx/ioctl.c > index b65ab214bdf5..c542d4dd3e64 100644 > --- a/arch/x86/kernel/cpu/sgx/ioctl.c > +++ b/arch/x86/kernel/cpu/sgx/ioctl.c > @@ -1142,6 +1142,7 @@ static long sgx_encl_remove_pages(struct sgx_encl > *encl, > * Do not keep encl->lock because of dependency on > * mmap_lock acquired in sgx_zap_enclave_ptes(). > */ > + entry->desc |= SGX_ENCL_PAGE_BEING_REMOVED; > mutex_unlock(&encl->lock); > sgx_zap_enclave_ptes(encl, addr); Reviewed-by: Haitao Huang