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=-20.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 B04CCC4361B for ; Tue, 8 Dec 2020 15:08:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7004C23A75 for ; Tue, 8 Dec 2020 15:08:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730017AbgLHPIV (ORCPT ); Tue, 8 Dec 2020 10:08:21 -0500 Received: from pegase1.c-s.fr ([93.17.236.30]:21575 "EHLO pegase1.c-s.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729752AbgLHPIV (ORCPT ); Tue, 8 Dec 2020 10:08:21 -0500 Received: from localhost (mailhub1-int [192.168.12.234]) by localhost (Postfix) with ESMTP id 4Cr3Sg3cv5zB09b2; Tue, 8 Dec 2020 16:07:31 +0100 (CET) X-Virus-Scanned: Debian amavisd-new at c-s.fr Received: from pegase1.c-s.fr ([192.168.12.234]) by localhost (pegase1.c-s.fr [192.168.12.234]) (amavisd-new, port 10024) with ESMTP id UYOh8aFLsijv; Tue, 8 Dec 2020 16:07:31 +0100 (CET) Received: from messagerie.si.c-s.fr (messagerie.si.c-s.fr [192.168.25.192]) by pegase1.c-s.fr (Postfix) with ESMTP id 4Cr3Sg2BXlzB09b1; Tue, 8 Dec 2020 16:07:31 +0100 (CET) Received: from localhost (localhost [127.0.0.1]) by messagerie.si.c-s.fr (Postfix) with ESMTP id B88228B7C8; Tue, 8 Dec 2020 16:07:32 +0100 (CET) X-Virus-Scanned: amavisd-new at c-s.fr Received: from messagerie.si.c-s.fr ([127.0.0.1]) by localhost (messagerie.si.c-s.fr [127.0.0.1]) (amavisd-new, port 10023) with ESMTP id kjdz0ODqg8li; Tue, 8 Dec 2020 16:07:32 +0100 (CET) Received: from [192.168.4.90] (unknown [192.168.4.90]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 10FDB8B7BE; Tue, 8 Dec 2020 16:07:32 +0100 (CET) Subject: Re: [PATCH v3 4/5] powerpc/fault: Avoid heavy search_exception_tables() verification To: "Aneesh Kumar K.V" , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , npiggin@gmail.com Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org References: <0d37490a067840f53fc5b118869917c0aec9ab87.1607416578.git.christophe.leroy@csgroup.eu> <731bdee26a5a5c81cd815ed624a6fb3bdef8b4db.1607416578.git.christophe.leroy@csgroup.eu> <87lfe8qrik.fsf@linux.ibm.com> From: Christophe Leroy Message-ID: Date: Tue, 8 Dec 2020 16:07:32 +0100 User-Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.5.1 MIME-Version: 1.0 In-Reply-To: <87lfe8qrik.fsf@linux.ibm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: fr Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Le 08/12/2020 à 15:52, Aneesh Kumar K.V a écrit : > Christophe Leroy writes: > >> search_exception_tables() is an heavy operation, we have to avoid it. >> When KUAP is selected, we'll know the fault has been blocked by KUAP. >> Otherwise, it behaves just as if the address was already in the TLBs >> and no fault was generated. >> >> Signed-off-by: Christophe Leroy >> Reviewed-by: Nicholas Piggin >> --- >> v3: rebased >> v2: Squashed with the preceeding patch which was re-ordering tests that get removed in this patch. >> --- >> arch/powerpc/mm/fault.c | 23 +++++++---------------- >> 1 file changed, 7 insertions(+), 16 deletions(-) >> >> diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c >> index 3fcd34c28e10..1770b41e4730 100644 >> --- a/arch/powerpc/mm/fault.c >> +++ b/arch/powerpc/mm/fault.c >> @@ -210,28 +210,19 @@ static bool bad_kernel_fault(struct pt_regs *regs, unsigned long error_code, >> return true; >> } >> >> - if (!is_exec && address < TASK_SIZE && (error_code & (DSISR_PROTFAULT | DSISR_KEYFAULT)) && >> - !search_exception_tables(regs->nip)) { >> - pr_crit_ratelimited("Kernel attempted to access user page (%lx) - exploit attempt? (uid: %d)\n", >> - address, >> - from_kuid(&init_user_ns, current_uid())); >> - } >> - >> // Kernel fault on kernel address is bad >> if (address >= TASK_SIZE) >> return true; >> >> - // Fault on user outside of certain regions (eg. copy_tofrom_user()) is bad >> - if (!search_exception_tables(regs->nip)) >> - return true; >> - >> - // Read/write fault in a valid region (the exception table search passed >> - // above), but blocked by KUAP is bad, it can never succeed. >> - if (bad_kuap_fault(regs, address, is_write)) >> + // Read/write fault blocked by KUAP is bad, it can never succeed. >> + if (bad_kuap_fault(regs, address, is_write)) { >> + pr_crit_ratelimited("Kernel attempted to %s user page (%lx) - exploit attempt? (uid: %d)\n", >> + is_write ? "write" : "read", address, >> + from_kuid(&init_user_ns, current_uid())); >> return true; >> + } > > > With this I am wondering whether the WARN() in bad_kuap_fault() is > needed. A direct access of userspace address will trigger this, whereas > previously we used bad_kuap_fault() only to identify incorrect restore > of AMR register (ie, to identify kernel bugs). Hence a WARN() there was > useful. We loose that differentiation now? Yes, I wanted to remove the WARN(), see https://patchwork.ozlabs.org/project/linuxppc-dev/patch/cc9129bdda1dbc2f0a09cf45fece7d0b0e690784.1605541983.git.christophe.leroy@csgroup.eu/ but I understood from Michael that maybe it was not a good idea, so I left it aside for now when rebasing to v3. Yes previously we were able to differentiate between a direct access of userspace and a valid access triggering a KUAP fault, but at the cost of the heavy search_exception_tables(). The issue was reported by Nick through https://github.com/linuxppc/issues/issues/317 Should be perform the search_exception_tables() once we have hit the KUAP fault and WARN() only in that case ? I was wondering also if we should keep the WARN() only when CONFIG_PPC_KUAP_DEBUG is set ? > > >> >> - // What's left? Kernel fault on user in well defined regions (extable >> - // matched), and allowed by KUAP in the faulting context. >> + // What's left? Kernel fault on user and allowed by KUAP in the faulting context. >> return false; >> } >> >> -- >> 2.25.0 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=-20.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 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 DB898C433FE for ; Tue, 8 Dec 2020 15:09:30 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 2025823A6C for ; Tue, 8 Dec 2020 15:09:30 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2025823A6C Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=csgroup.eu Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from bilbo.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 4Cr3Vw1bJYzDqdj for ; Wed, 9 Dec 2020 02:09:28 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=csgroup.eu (client-ip=93.17.236.30; helo=pegase1.c-s.fr; envelope-from=christophe.leroy@csgroup.eu; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=csgroup.eu Received: from pegase1.c-s.fr (pegase1.c-s.fr [93.17.236.30]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4Cr3St3CVdzDqTk for ; Wed, 9 Dec 2020 02:07:36 +1100 (AEDT) Received: from localhost (mailhub1-int [192.168.12.234]) by localhost (Postfix) with ESMTP id 4Cr3Sg3cv5zB09b2; Tue, 8 Dec 2020 16:07:31 +0100 (CET) X-Virus-Scanned: Debian amavisd-new at c-s.fr Received: from pegase1.c-s.fr ([192.168.12.234]) by localhost (pegase1.c-s.fr [192.168.12.234]) (amavisd-new, port 10024) with ESMTP id UYOh8aFLsijv; Tue, 8 Dec 2020 16:07:31 +0100 (CET) Received: from messagerie.si.c-s.fr (messagerie.si.c-s.fr [192.168.25.192]) by pegase1.c-s.fr (Postfix) with ESMTP id 4Cr3Sg2BXlzB09b1; Tue, 8 Dec 2020 16:07:31 +0100 (CET) Received: from localhost (localhost [127.0.0.1]) by messagerie.si.c-s.fr (Postfix) with ESMTP id B88228B7C8; Tue, 8 Dec 2020 16:07:32 +0100 (CET) X-Virus-Scanned: amavisd-new at c-s.fr Received: from messagerie.si.c-s.fr ([127.0.0.1]) by localhost (messagerie.si.c-s.fr [127.0.0.1]) (amavisd-new, port 10023) with ESMTP id kjdz0ODqg8li; Tue, 8 Dec 2020 16:07:32 +0100 (CET) Received: from [192.168.4.90] (unknown [192.168.4.90]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 10FDB8B7BE; Tue, 8 Dec 2020 16:07:32 +0100 (CET) Subject: Re: [PATCH v3 4/5] powerpc/fault: Avoid heavy search_exception_tables() verification To: "Aneesh Kumar K.V" , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , npiggin@gmail.com References: <0d37490a067840f53fc5b118869917c0aec9ab87.1607416578.git.christophe.leroy@csgroup.eu> <731bdee26a5a5c81cd815ed624a6fb3bdef8b4db.1607416578.git.christophe.leroy@csgroup.eu> <87lfe8qrik.fsf@linux.ibm.com> From: Christophe Leroy Message-ID: Date: Tue, 8 Dec 2020 16:07:32 +0100 User-Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.5.1 MIME-Version: 1.0 In-Reply-To: <87lfe8qrik.fsf@linux.ibm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: fr Content-Transfer-Encoding: 8bit X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Le 08/12/2020 à 15:52, Aneesh Kumar K.V a écrit : > Christophe Leroy writes: > >> search_exception_tables() is an heavy operation, we have to avoid it. >> When KUAP is selected, we'll know the fault has been blocked by KUAP. >> Otherwise, it behaves just as if the address was already in the TLBs >> and no fault was generated. >> >> Signed-off-by: Christophe Leroy >> Reviewed-by: Nicholas Piggin >> --- >> v3: rebased >> v2: Squashed with the preceeding patch which was re-ordering tests that get removed in this patch. >> --- >> arch/powerpc/mm/fault.c | 23 +++++++---------------- >> 1 file changed, 7 insertions(+), 16 deletions(-) >> >> diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c >> index 3fcd34c28e10..1770b41e4730 100644 >> --- a/arch/powerpc/mm/fault.c >> +++ b/arch/powerpc/mm/fault.c >> @@ -210,28 +210,19 @@ static bool bad_kernel_fault(struct pt_regs *regs, unsigned long error_code, >> return true; >> } >> >> - if (!is_exec && address < TASK_SIZE && (error_code & (DSISR_PROTFAULT | DSISR_KEYFAULT)) && >> - !search_exception_tables(regs->nip)) { >> - pr_crit_ratelimited("Kernel attempted to access user page (%lx) - exploit attempt? (uid: %d)\n", >> - address, >> - from_kuid(&init_user_ns, current_uid())); >> - } >> - >> // Kernel fault on kernel address is bad >> if (address >= TASK_SIZE) >> return true; >> >> - // Fault on user outside of certain regions (eg. copy_tofrom_user()) is bad >> - if (!search_exception_tables(regs->nip)) >> - return true; >> - >> - // Read/write fault in a valid region (the exception table search passed >> - // above), but blocked by KUAP is bad, it can never succeed. >> - if (bad_kuap_fault(regs, address, is_write)) >> + // Read/write fault blocked by KUAP is bad, it can never succeed. >> + if (bad_kuap_fault(regs, address, is_write)) { >> + pr_crit_ratelimited("Kernel attempted to %s user page (%lx) - exploit attempt? (uid: %d)\n", >> + is_write ? "write" : "read", address, >> + from_kuid(&init_user_ns, current_uid())); >> return true; >> + } > > > With this I am wondering whether the WARN() in bad_kuap_fault() is > needed. A direct access of userspace address will trigger this, whereas > previously we used bad_kuap_fault() only to identify incorrect restore > of AMR register (ie, to identify kernel bugs). Hence a WARN() there was > useful. We loose that differentiation now? Yes, I wanted to remove the WARN(), see https://patchwork.ozlabs.org/project/linuxppc-dev/patch/cc9129bdda1dbc2f0a09cf45fece7d0b0e690784.1605541983.git.christophe.leroy@csgroup.eu/ but I understood from Michael that maybe it was not a good idea, so I left it aside for now when rebasing to v3. Yes previously we were able to differentiate between a direct access of userspace and a valid access triggering a KUAP fault, but at the cost of the heavy search_exception_tables(). The issue was reported by Nick through https://github.com/linuxppc/issues/issues/317 Should be perform the search_exception_tables() once we have hit the KUAP fault and WARN() only in that case ? I was wondering also if we should keep the WARN() only when CONFIG_PPC_KUAP_DEBUG is set ? > > >> >> - // What's left? Kernel fault on user in well defined regions (extable >> - // matched), and allowed by KUAP in the faulting context. >> + // What's left? Kernel fault on user and allowed by KUAP in the faulting context. >> return false; >> } >> >> -- >> 2.25.0