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=-9.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 3729DC4360C for ; Fri, 11 Oct 2019 02:24:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0F00E2054F for ; Fri, 11 Oct 2019 02:24:56 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=ellerman.id.au header.i=@ellerman.id.au header.b="q0NvSh62" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728078AbfJKCYy (ORCPT ); Thu, 10 Oct 2019 22:24:54 -0400 Received: from ozlabs.org ([203.11.71.1]:37595 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727813AbfJKCYy (ORCPT ); Thu, 10 Oct 2019 22:24:54 -0400 Received: by ozlabs.org (Postfix, from userid 1034) id 46qBcM5Rcjz9sPJ; Fri, 11 Oct 2019 13:24:51 +1100 (AEDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ellerman.id.au; s=201909; t=1570760691; bh=eEXnHboAKeL3t3V8Dxhyp5Ij7LkGXdOie9uDbo+nsGE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=q0NvSh6264LaH69u9aCpvAoVlx4MHB2gLx3LWm6UwcZ+DqfYphfOT44Vtb11K+R7p HuVONuIU8gT/Dhw6lX3ZYu86Y+sEeCMkMTSd4q0mpx9KcOnv406A2Ts4ZTjmFVHNaO 8KEXXINfilP9QPjzrjYRQCMwvb70paNrLg/hsvTvEe7P/C8Q4Bw249vjXGIvQGbGIJ 78gTGiDPQlE048CaVdQKgiOUmkJa4VlQedEtu9Kf2XBRiFzlFLklnPignkbFj4rxpO hVSoOlp4wPZvqJNZILZsxpuW8y4HbxI/dNNCTzga1PcZEPiX+kXN5bMnqIw1f1SKcC 5hTicPLNpAiNA== From: Michael Ellerman To: cyphar@cyphar.com Cc: mingo@redhat.com, peterz@infradead.org, alexander.shishkin@linux.intel.com, jolsa@redhat.com, namhyung@kernel.org, christian@brauner.io, keescook@chromium.org, linux@rasmusvillemoes.dk, viro@zeniv.linux.org.uk, torvalds@linux-foundation.org, libc-alpha@sourceware.org, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] usercopy: Avoid soft lockups in test_check_nonzero_user() Date: Fri, 11 Oct 2019 13:24:47 +1100 Message-Id: <20191011022447.24249-1-mpe@ellerman.id.au> X-Mailer: git-send-email 2.21.0 In-Reply-To: <20191010114007.o3bygjf4jlfk242e@yavin.dot.cyphar.com> References: <20191010114007.o3bygjf4jlfk242e@yavin.dot.cyphar.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On a machine with a 64K PAGE_SIZE, the nested for loops in test_check_nonzero_user() can lead to soft lockups, eg: watchdog: BUG: soft lockup - CPU#4 stuck for 22s! [modprobe:611] Modules linked in: test_user_copy(+) vmx_crypto gf128mul crc32c_vpmsum virtio_balloon ip_tables x_tables autofs4 CPU: 4 PID: 611 Comm: modprobe Tainted: G L 5.4.0-rc1-gcc-8.2.0-00001-gf5a1a536fa14-dirty #1151 ... NIP __might_sleep+0x20/0xc0 LR __might_fault+0x40/0x60 Call Trace: check_zeroed_user+0x12c/0x200 test_user_copy_init+0x67c/0x1210 [test_user_copy] do_one_initcall+0x60/0x340 do_init_module+0x7c/0x2f0 load_module+0x2d94/0x30e0 __do_sys_finit_module+0xc8/0x150 system_call+0x5c/0x68 Even with a 4K PAGE_SIZE the test takes multiple seconds. Instead tweak it to only scan a 1024 byte region, but make it cross the page boundary. Fixes: f5a1a536fa14 ("lib: introduce copy_struct_from_user() helper") Suggested-by: Aleksa Sarai Signed-off-by: Michael Ellerman --- lib/test_user_copy.c | 23 ++++++++++++++++++++--- 1 file changed, 20 insertions(+), 3 deletions(-) How does this look? It runs in < 1s on my machine here. cheers diff --git a/lib/test_user_copy.c b/lib/test_user_copy.c index 950ee88cd6ac..9fb6bc609d4c 100644 --- a/lib/test_user_copy.c +++ b/lib/test_user_copy.c @@ -47,9 +47,26 @@ static bool is_zeroed(void *from, size_t size) static int test_check_nonzero_user(char *kmem, char __user *umem, size_t size) { int ret = 0; - size_t start, end, i; - size_t zero_start = size / 4; - size_t zero_end = size - zero_start; + size_t start, end, i, zero_start, zero_end; + + if (test(size < 1024, "buffer too small")) + return -EINVAL; + + /* + * We want to cross a page boundary to exercise the code more + * effectively. We assume the buffer we're passed has a page boundary at + * size / 2. We also don't want to make the size we scan too large, + * otherwise the test can take a long time and cause soft lockups. So + * scan a 1024 byte region across the page boundary. + */ + start = size / 2 - 512; + size = 1024; + + kmem += start; + umem += start; + + zero_start = size / 4; + zero_end = size - zero_start; /* * We conduct a series of check_nonzero_user() tests on a block of memory -- 2.21.0