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=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 0BECEC433FE for ; Tue, 8 Dec 2020 01:53:37 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 1C4E62388C for ; Tue, 8 Dec 2020 01:53:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1C4E62388C Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ellerman.id.au Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 3BD368D0003; Mon, 7 Dec 2020 20:53:35 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 36CC78D0002; Mon, 7 Dec 2020 20:53:35 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 282478D0003; Mon, 7 Dec 2020 20:53:35 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id 0F97D8D0002 for ; Mon, 7 Dec 2020 20:53:35 -0500 (EST) Received: from smtpin08.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id C8E441EE6 for ; Tue, 8 Dec 2020 01:53:34 +0000 (UTC) X-FDA: 77568443148.08.vase78_2c10df5273e3 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin08.hostedemail.com (Postfix) with ESMTP id ACFC61819E769 for ; Tue, 8 Dec 2020 01:53:34 +0000 (UTC) X-HE-Tag: vase78_2c10df5273e3 X-Filterd-Recvd-Size: 8793 Received: from ozlabs.org (ozlabs.org [203.11.71.1]) by imf30.hostedemail.com (Postfix) with ESMTP for ; Tue, 8 Dec 2020 01:53:33 +0000 (UTC) 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 4CqjrT6Pf8z9sVq; Tue, 8 Dec 2020 12:53:29 +1100 (AEDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ellerman.id.au; s=201909; t=1607392410; bh=/8fzuBFuhiqxQcy7MGCMXjTyb3lmQJxFfjSeU8VC/pA=; h=From:To:Cc:Subject:In-Reply-To:References:Date:From; b=TbTBlvrFV1uDoRlxjjTB6rncl1ont6GikRxWloW5MkJ4LA56t31A+3YqDJyBh5EVO MstQR1u4StQ5q5AAtE6LWmhSIJBMiry1eDhW1hY/Jpno/6v6UdVlVJwxIPc0n3gagF vxMoMa+Wdi0MerT5GXRzwlTXpTcIJjo5PI2xcrV1UBEZgtmuCe8DuMnTsP7Qk4hf+A i0lJRVxBy2EaYvlHrZwN8w/HGalp69rGaSbWZipVT4/K2Sy8hNe2FrSyLUkdnaIsps 4JtqcD9Zl+nHN3UphMmV+mZyyCLvMJ+fAkkzEvwuXOnQ7cO78Fumt4X1Vd1nkm78KB CqLChmOxyzwyA== 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: <87ft4itqdw.fsf@mpe.ellerman.id.au> Date: Tue, 08 Dec 2020 12:53:26 +1100 Message-ID: <87a6upt65l.fsf@mpe.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Christophe Leroy writes: > Le 07/12/2020 =C3=A0 01:24, Michael Ellerman a =C3=A9crit=C2=A0: >> 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/noh= ash/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 5.1= 0.0-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 0000= 0001 c09865e8 c092e640 >>> [ 1117.202899] GPR08: 00001032 00000000 00000000 00014efc 28082224 100d= 166a 100a0920 00000000 >>> [ 1117.202899] GPR16: 100cac0c 100b0000 1080c3fc 1080d685 100d0000 100d= 0000 00000000 100a0900 >>> [ 1117.202899] GPR24: 100d0000 c07892ec 00000000 c0921510 c21f4440 0000= 005c 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 (unrelia= ble) >>> [ 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: 0000= 0000 >>> [ 1117.205416] DAR: 0000005c DSISR: c0000000 >>> [ 1117.205416] GPR00: c0045948 cacdbd38 c2929290 00000001 00000017 0000= 0017 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 (unre= liable) >>> [ 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: 0= 0000000 >>> [ 1117.208470] >>> [ 1117.208470] GPR00: 00000004 7fc34090 77bfb4e0 00000001 1080fa40 0000= 0002 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 73= c90040 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 s= ize) >>> +{ >>> + return (unsigned long)unsafe_src >=3D TASK_SIZE_MAX; >>> +} >>=20 >> Is there a reason we're using TASK_SIZE_MAX? > > No special reason, that's just copied from x86. > >> 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? > > Yes, on PPC64 that's right. On PPC32 the kernel memory starts where the u= serland stops. Yep sorry I was talking about 64-bit there. >> We have is_kernel_addr() which already encapsulates some platform quirks >> around that logic, it seems like it would be a better fit? > > Yes probably, I send v2. For PPC32 that's a comparison with TASK_SIZE tho= ught. Yeah, so it's the same test for PPC32 but I think is_kernel_addr() is better on 64-bit. I'll grab your v2. cheers