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[2001:44b8:111e:5c00:5199:f2bf:3cbb:22e6]) by smtp.gmail.com with ESMTPSA id o20sm4304026pjs.2.2021.03.25.15.44.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 25 Mar 2021 15:44:58 -0700 (PDT) From: Daniel Axtens To: Christophe Leroy , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org Subject: Re: [PATCH v2 07/15] powerpc/uaccess: Call might_fault() inconditionaly In-Reply-To: <874kgykgfk.fsf@dja-thinkpad.axtens.net> References: <874kgykgfk.fsf@dja-thinkpad.axtens.net> Date: Fri, 26 Mar 2021 09:44:54 +1100 Message-ID: <871rc2kg49.fsf@dja-thinkpad.axtens.net> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Daniel Axtens writes: > Hi Christophe, > >> Commit 6bfd93c32a50 ("powerpc: Fix incorrect might_sleep in >> __get_user/__put_user on kernel addresses") added a check to not call >> might_sleep() on kernel addresses. This was to enable the use of >> __get_user() in the alignment exception handler for any address. >> >> Then commit 95156f0051cb ("lockdep, mm: fix might_fault() annotation") >> added a check of the address space in might_fault(), based on >> set_fs() logic. But this didn't solve the powerpc alignment exception >> case as it didn't call set_fs(KERNEL_DS). >> >> Nowadays, set_fs() is gone, previous patch fixed the alignment >> exception handler and __get_user/__put_user are not supposed to be >> used anymore to read kernel memory. >> >> Therefore the is_kernel_addr() check has become useless and can be >> removed. > > While I agree that __get_user/__put_user should not be used on kernel > memory, I'm not sure that we have covered every case where they might be > used on kernel memory yet. I did a git grep for __get_user - there are > several callers in arch/powerpc and it looks like at least lib/sstep.c > might be using __get_user to read kernel memory while single-stepping. > > I am not sure if might_sleep has got logic to cover the powerpc case - > it uses uaccess_kernel, but we don't supply a definition for that on > powerpc, so if we do end up calling __get_user on a kernel address, I > think we might now throw a warning. (Unless we are saved by > pagefault_disabled()?) Ah, I just re-read some of my earlier emails and was reminded that yes, if we are calling __get/put, we must have disabled page faults. So yes, this is good. > > (But I haven't tested this yet, so it's possible I misunderstood > something.) > > Do you expect any consequences if we've missed a case where > __(get|put)_user is called on a kernel address because it hasn't been > converted to use better helpers yet? > > Kind regards, > Daniel > >> >> Signed-off-by: Christophe Leroy >> --- >> arch/powerpc/include/asm/uaccess.h | 9 ++++----- >> 1 file changed, 4 insertions(+), 5 deletions(-) >> >> diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h >> index eaa828a6a419..c4bbc64758a0 100644 >> --- a/arch/powerpc/include/asm/uaccess.h >> +++ b/arch/powerpc/include/asm/uaccess.h >> @@ -77,8 +77,7 @@ __pu_failed: \ >> __typeof__(*(ptr)) __pu_val = (x); \ >> __typeof__(size) __pu_size = (size); \ >> \ >> - if (!is_kernel_addr((unsigned long)__pu_addr)) \ >> - might_fault(); \ >> + might_fault(); \ >> __chk_user_ptr(__pu_addr); \ >> __put_user_size(__pu_val, __pu_addr, __pu_size, __pu_err); \ >> \ >> @@ -238,12 +237,12 @@ do { \ >> __typeof__(size) __gu_size = (size); \ >> \ >> __chk_user_ptr(__gu_addr); \ >> - if (do_allow && !is_kernel_addr((unsigned long)__gu_addr)) \ >> + if (do_allow) { \ >> might_fault(); \ >> - if (do_allow) \ >> __get_user_size(__gu_val, __gu_addr, __gu_size, __gu_err); \ >> - else \ >> + } else { \ >> __get_user_size_allowed(__gu_val, __gu_addr, __gu_size, __gu_err); \ >> + } \ One microscopic nit: these changes throw the '\'s further out of alignment. Reviewed-by: Daniel Axtens Kind regards, Daniel >> (x) = (__typeof__(*(ptr)))__gu_val; \ >> \ >> __gu_err; \ >> -- >> 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=-13.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 5FF07C433DB for ; Thu, 25 Mar 2021 22:45:30 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (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 CE1BD61A0F for ; Thu, 25 Mar 2021 22:45:29 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CE1BD61A0F Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=axtens.net Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4F60Yh39Pgz3byw for ; Fri, 26 Mar 2021 09:45:28 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; dkim=fail reason="signature verification failed" (1024-bit key; unprotected) header.d=axtens.net header.i=@axtens.net header.a=rsa-sha256 header.s=google header.b=IicXkfu1; dkim-atps=neutral Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=axtens.net (client-ip=2607:f8b0:4864:20::42a; helo=mail-pf1-x42a.google.com; envelope-from=dja@axtens.net; receiver=) Authentication-Results: lists.ozlabs.org; dkim=pass (1024-bit key; unprotected) header.d=axtens.net header.i=@axtens.net header.a=rsa-sha256 header.s=google header.b=IicXkfu1; dkim-atps=neutral Received: from mail-pf1-x42a.google.com (mail-pf1-x42a.google.com [IPv6:2607:f8b0:4864:20::42a]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4F60YD2249z303X for ; Fri, 26 Mar 2021 09:45:01 +1100 (AEDT) Received: by mail-pf1-x42a.google.com with SMTP id l123so3536418pfl.8 for ; Thu, 25 Mar 2021 15:45:01 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=axtens.net; s=google; h=from:to:cc:subject:in-reply-to:references:date:message-id :mime-version; bh=i1A3B1VA5Zv5sBwoUoS9WZiP910FQdZZhnQVANdwB9c=; b=IicXkfu18EISqV5ydhu56kRQMXqHpoRlop4C6BcDh/WNhGYMdJzZ/j9kZAfuPT4BQ/ npjBX182kJUDvhCs3A14H6ZmbO6bikVoZBMzyFhHP3JHmK2ypCwwuYKXo48N26dOflJz sF9QIO5+3JINV4A5ZlwLXVEoUJCE0XxMhc7Us= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:in-reply-to:references:date :message-id:mime-version; bh=i1A3B1VA5Zv5sBwoUoS9WZiP910FQdZZhnQVANdwB9c=; b=SwfIfyApH6CNDa6J9E8Kddsp4FwOfgZGKpESOoV6i3wsWWOoZ7wR1/cdZrGau16aJ5 CdBvRoNFTzHEqpBbFhhW9AL5KV7/kc3zXh7VWXjx+FgTkoJpCCwo5z7CduD64ZccG2zv eZJyrfGKJtEBqHC+sVFK2nTXExqiA2EoBw3jDzBPQOP8gYBJsuaMm1RXlThv3khxL5XM N2n0WhzHThkIHhNdT8Is5hGHbxGvIyxOdCz60c5ONQvV5I4accUbh8eM4QYOExrPgDBG UhNj2C2/kOpW1t+BXgLczexBzt1oIxfF1ewdZaONbKwmQg5IzrjYSwZCT6tvJaGtbXOf OfsQ== X-Gm-Message-State: AOAM533O5XMK1IoahdwyOwIC2yEg5929xOQBzg+orIN6hmT3CcPW5/6j rk2TvTU0hsluv71df+y72rcbHA== X-Google-Smtp-Source: ABdhPJzl6JZCX5R+lL7U/Se0bnk4N2jLloez48zhqiROs1PEF9zolxztpZkiesZDt5uQTPGMyTaL1w== X-Received: by 2002:a17:902:da81:b029:e5:de44:af5b with SMTP id j1-20020a170902da81b02900e5de44af5bmr12069109plx.27.1616712298559; Thu, 25 Mar 2021 15:44:58 -0700 (PDT) Received: from localhost (2001-44b8-111e-5c00-5199-f2bf-3cbb-22e6.static.ipv6.internode.on.net. [2001:44b8:111e:5c00:5199:f2bf:3cbb:22e6]) by smtp.gmail.com with ESMTPSA id o20sm4304026pjs.2.2021.03.25.15.44.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 25 Mar 2021 15:44:58 -0700 (PDT) From: Daniel Axtens To: Christophe Leroy , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman Subject: Re: [PATCH v2 07/15] powerpc/uaccess: Call might_fault() inconditionaly In-Reply-To: <874kgykgfk.fsf@dja-thinkpad.axtens.net> References: <874kgykgfk.fsf@dja-thinkpad.axtens.net> Date: Fri, 26 Mar 2021 09:44:54 +1100 Message-ID: <871rc2kg49.fsf@dja-thinkpad.axtens.net> MIME-Version: 1.0 Content-Type: text/plain 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" Daniel Axtens writes: > Hi Christophe, > >> Commit 6bfd93c32a50 ("powerpc: Fix incorrect might_sleep in >> __get_user/__put_user on kernel addresses") added a check to not call >> might_sleep() on kernel addresses. This was to enable the use of >> __get_user() in the alignment exception handler for any address. >> >> Then commit 95156f0051cb ("lockdep, mm: fix might_fault() annotation") >> added a check of the address space in might_fault(), based on >> set_fs() logic. But this didn't solve the powerpc alignment exception >> case as it didn't call set_fs(KERNEL_DS). >> >> Nowadays, set_fs() is gone, previous patch fixed the alignment >> exception handler and __get_user/__put_user are not supposed to be >> used anymore to read kernel memory. >> >> Therefore the is_kernel_addr() check has become useless and can be >> removed. > > While I agree that __get_user/__put_user should not be used on kernel > memory, I'm not sure that we have covered every case where they might be > used on kernel memory yet. I did a git grep for __get_user - there are > several callers in arch/powerpc and it looks like at least lib/sstep.c > might be using __get_user to read kernel memory while single-stepping. > > I am not sure if might_sleep has got logic to cover the powerpc case - > it uses uaccess_kernel, but we don't supply a definition for that on > powerpc, so if we do end up calling __get_user on a kernel address, I > think we might now throw a warning. (Unless we are saved by > pagefault_disabled()?) Ah, I just re-read some of my earlier emails and was reminded that yes, if we are calling __get/put, we must have disabled page faults. So yes, this is good. > > (But I haven't tested this yet, so it's possible I misunderstood > something.) > > Do you expect any consequences if we've missed a case where > __(get|put)_user is called on a kernel address because it hasn't been > converted to use better helpers yet? > > Kind regards, > Daniel > >> >> Signed-off-by: Christophe Leroy >> --- >> arch/powerpc/include/asm/uaccess.h | 9 ++++----- >> 1 file changed, 4 insertions(+), 5 deletions(-) >> >> diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h >> index eaa828a6a419..c4bbc64758a0 100644 >> --- a/arch/powerpc/include/asm/uaccess.h >> +++ b/arch/powerpc/include/asm/uaccess.h >> @@ -77,8 +77,7 @@ __pu_failed: \ >> __typeof__(*(ptr)) __pu_val = (x); \ >> __typeof__(size) __pu_size = (size); \ >> \ >> - if (!is_kernel_addr((unsigned long)__pu_addr)) \ >> - might_fault(); \ >> + might_fault(); \ >> __chk_user_ptr(__pu_addr); \ >> __put_user_size(__pu_val, __pu_addr, __pu_size, __pu_err); \ >> \ >> @@ -238,12 +237,12 @@ do { \ >> __typeof__(size) __gu_size = (size); \ >> \ >> __chk_user_ptr(__gu_addr); \ >> - if (do_allow && !is_kernel_addr((unsigned long)__gu_addr)) \ >> + if (do_allow) { \ >> might_fault(); \ >> - if (do_allow) \ >> __get_user_size(__gu_val, __gu_addr, __gu_size, __gu_err); \ >> - else \ >> + } else { \ >> __get_user_size_allowed(__gu_val, __gu_addr, __gu_size, __gu_err); \ >> + } \ One microscopic nit: these changes throw the '\'s further out of alignment. Reviewed-by: Daniel Axtens Kind regards, Daniel >> (x) = (__typeof__(*(ptr)))__gu_val; \ >> \ >> __gu_err; \ >> -- >> 2.25.0