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=-15.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 9AFBDC433FE for ; Mon, 7 Dec 2020 00:25:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 52A3B2063A for ; Mon, 7 Dec 2020 00:25:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728372AbgLGAY7 (ORCPT ); Sun, 6 Dec 2020 19:24:59 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51240 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726046AbgLGAY7 (ORCPT ); Sun, 6 Dec 2020 19:24:59 -0500 Received: from ozlabs.org (bilbo.ozlabs.org [IPv6:2401:3900:2:1::2]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A5BB1C0613D0 for ; Sun, 6 Dec 2020 16:24:18 -0800 (PST) Received: from authenticated.ozlabs.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (P-256) server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by mail.ozlabs.org (Postfix) with ESMTPSA id 4Cq3vy3jzrz9sVs; Mon, 7 Dec 2020 11:24:14 +1100 (AEDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ellerman.id.au; s=201909; t=1607300656; bh=rXQ3gqfHXQJWyBKIu3JFIYX0lUK5ayh53oBxpJvzaNI=; h=From:To:Cc:Subject:In-Reply-To:References:Date:From; b=DuixQ65KPhTRyeeE92ETm51FUQPPKWTqK0Y0jT9c+WouAKrgJQqYUrXZ/l2f5KmtL 8qNCEpwnfNweqvhTKtAPpy1yK54p3JsABrFOgjChF+hM0Dvlg8YwQ8TB7MvmmfYNqp du2IEAfHkLkzXK7gAs2fCu2fjgig9qLTG7cUx5NquzskHCbOOkJEmT41prLGQGEsrN ktk+FJc/1vvFk0q0sACmmwba5pxlZ/P9+xyXU/pbT9g6fDm2Wm5vtsT3vdLfH5fMlf I20YXRjRWZ4ou9+OZSWffcyDam0q0BoOvr4b/Ug73q9YoGnRfiYoPNZMpVhDKvY7yR TbGMKpgPUEZZA== From: Michael Ellerman To: Christophe Leroy , Benjamin Herrenschmidt , Paul Mackerras , hch@lst.de, viro@zeniv.linux.org.uk, akpm@linux-foundation.org Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org Subject: Re: [PATCH] powerpc/mm: Fix KUAP warning by providing copy_from_kernel_nofault_allowed() In-Reply-To: References: Date: Mon, 07 Dec 2020 11:24:11 +1100 Message-ID: <87ft4itqdw.fsf@mpe.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Christophe Leroy writes: > Since commit c33165253492 ("powerpc: use non-set_fs based maccess > routines"), userspace access is not granted anymore when using > copy_from_kernel_nofault() > > However, kthread_probe_data() uses copy_from_kernel_nofault() > to check validity of pointers. When the pointer is NULL, > it points to userspace, leading to a KUAP fault and triggering > the following big hammer warning many times when you request > a sysrq "show task": > > [ 1117.202054] ------------[ cut here ]------------ > [ 1117.202102] Bug: fault blocked by AP register ! > [ 1117.202261] WARNING: CPU: 0 PID: 377 at arch/powerpc/include/asm/nohash/32/kup-8xx.h:66 do_page_fault+0x4a8/0x5ec > [ 1117.202310] Modules linked in: > [ 1117.202428] CPU: 0 PID: 377 Comm: sh Tainted: G W 5.10.0-rc5-01340-g83f53be2de31-dirty #4175 > [ 1117.202499] NIP: c0012048 LR: c0012048 CTR: 00000000 > [ 1117.202573] REGS: cacdbb88 TRAP: 0700 Tainted: G W (5.10.0-rc5-01340-g83f53be2de31-dirty) > [ 1117.202625] MSR: 00021032 CR: 24082222 XER: 20000000 > [ 1117.202899] > [ 1117.202899] GPR00: c0012048 cacdbc40 c2929290 00000023 c092e554 00000001 c09865e8 c092e640 > [ 1117.202899] GPR08: 00001032 00000000 00000000 00014efc 28082224 100d166a 100a0920 00000000 > [ 1117.202899] GPR16: 100cac0c 100b0000 1080c3fc 1080d685 100d0000 100d0000 00000000 100a0900 > [ 1117.202899] GPR24: 100d0000 c07892ec 00000000 c0921510 c21f4440 0000005c c0000000 cacdbc80 > [ 1117.204362] NIP [c0012048] do_page_fault+0x4a8/0x5ec > [ 1117.204461] LR [c0012048] do_page_fault+0x4a8/0x5ec > [ 1117.204509] Call Trace: > [ 1117.204609] [cacdbc40] [c0012048] do_page_fault+0x4a8/0x5ec (unreliable) > [ 1117.204771] [cacdbc70] [c00112f0] handle_page_fault+0x8/0x34 > [ 1117.204911] --- interrupt: 301 at copy_from_kernel_nofault+0x70/0x1c0 > [ 1117.204979] NIP: c010dbec LR: c010dbac CTR: 00000001 > [ 1117.205053] REGS: cacdbc80 TRAP: 0301 Tainted: G W (5.10.0-rc5-01340-g83f53be2de31-dirty) > [ 1117.205104] MSR: 00009032 CR: 28082224 XER: 00000000 > [ 1117.205416] DAR: 0000005c DSISR: c0000000 > [ 1117.205416] GPR00: c0045948 cacdbd38 c2929290 00000001 00000017 00000017 00000027 0000000f > [ 1117.205416] GPR08: c09926ec 00000000 00000000 3ffff000 24082224 > [ 1117.206106] NIP [c010dbec] copy_from_kernel_nofault+0x70/0x1c0 > [ 1117.206202] LR [c010dbac] copy_from_kernel_nofault+0x30/0x1c0 > [ 1117.206258] --- interrupt: 301 > [ 1117.206372] [cacdbd38] [c004bbb0] kthread_probe_data+0x44/0x70 (unreliable) > [ 1117.206561] [cacdbd58] [c0045948] print_worker_info+0xe0/0x194 > [ 1117.206717] [cacdbdb8] [c00548ac] sched_show_task+0x134/0x168 > [ 1117.206851] [cacdbdd8] [c005a268] show_state_filter+0x70/0x100 > [ 1117.206989] [cacdbe08] [c039baa0] sysrq_handle_showstate+0x14/0x24 > [ 1117.207122] [cacdbe18] [c039bf18] __handle_sysrq+0xac/0x1d0 > [ 1117.207257] [cacdbe48] [c039c0c0] write_sysrq_trigger+0x4c/0x74 > [ 1117.207407] [cacdbe68] [c01fba48] proc_reg_write+0xb4/0x114 > [ 1117.207550] [cacdbe88] [c0179968] vfs_write+0x12c/0x478 > [ 1117.207686] [cacdbf08] [c0179e60] ksys_write+0x78/0x128 > [ 1117.207826] [cacdbf38] [c00110d0] ret_from_syscall+0x0/0x34 > [ 1117.207938] --- interrupt: c01 at 0xfd4e784 > [ 1117.208008] NIP: 0fd4e784 LR: 0fe0f244 CTR: 10048d38 > [ 1117.208083] REGS: cacdbf48 TRAP: 0c01 Tainted: G W (5.10.0-rc5-01340-g83f53be2de31-dirty) > [ 1117.208134] MSR: 0000d032 CR: 44002222 XER: 00000000 > [ 1117.208470] > [ 1117.208470] GPR00: 00000004 7fc34090 77bfb4e0 00000001 1080fa40 00000002 7400000f fefefeff > [ 1117.208470] GPR08: 7f7f7f7f 10048d38 1080c414 7fc343c0 00000000 > [ 1117.209104] NIP [0fd4e784] 0xfd4e784 > [ 1117.209180] LR [0fe0f244] 0xfe0f244 > [ 1117.209236] --- interrupt: c01 > [ 1117.209274] Instruction dump: > [ 1117.209353] 714a4000 418200f0 73ca0001 40820084 73ca0032 408200f8 73c90040 4082ff60 > [ 1117.209727] 0fe00000 3c60c082 386399f4 48013b65 <0fe00000> 80010034 3860000b 7c0803a6 > [ 1117.210102] ---[ end trace 1927c0323393af3e ]--- > > To avoid that, copy_from_kernel_nofault_allowed() is used to check > whether the address is a valid kernel address. But the default > version of it returns true for any address. > > Provide a powerpc version of copy_from_kernel_nofault_allowed() > that returns false when the address is below TASK_USER_MAX, > so that copy_from_kernel_nofault() will return -ERANGE. > > Reported-by: Qian Cai > Fixes: c33165253492 ("powerpc: use non-set_fs based maccess routines") > Cc: Christoph Hellwig > Cc: Al Viro > Signed-off-by: Christophe Leroy > --- > This issue was introduced in 5.10. I didn't mark it for stable, hopping it will go into 5.10-rc7 > --- > arch/powerpc/mm/Makefile | 2 +- > arch/powerpc/mm/maccess.c | 9 +++++++++ > 2 files changed, 10 insertions(+), 1 deletion(-) > create mode 100644 arch/powerpc/mm/maccess.c > > diff --git a/arch/powerpc/mm/maccess.c b/arch/powerpc/mm/maccess.c > new file mode 100644 > index 000000000000..56e97c0fb233 > --- /dev/null > +++ b/arch/powerpc/mm/maccess.c > @@ -0,0 +1,9 @@ > +// SPDX-License-Identifier: GPL-2.0-only > + > +#include > +#include > + > +bool copy_from_kernel_nofault_allowed(const void *unsafe_src, size_t size) > +{ > + return (unsigned long)unsafe_src >= TASK_SIZE_MAX; > +} Is there a reason we're using TASK_SIZE_MAX? It's copy from *kernel* (nofault) allowed, so shouldn't we be checking that the address plausibly points at kernel memory? Not at no-man's land above TASK_SIZE_MAX but below the start of kernel memory? We have is_kernel_addr() which already encapsulates some platform quirks around that logic, it seems like it would be a better fit? ie: bool copy_from_kernel_nofault_allowed(const void *unsafe_src, size_t size) { return is_kernel_addr((unsigned long)unsafe_src); } cheers