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=-7.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, 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 124C9C433E0 for ; Sat, 16 May 2020 03:43:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E42A620756 for ; Sat, 16 May 2020 03:43:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589600586; bh=9Yr3NqlaT8J3yD/oIp4iOMhtlWnif5o5ocW4LHaILdM=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=EOEtYUE3xvBUc0p9TDDv23TEQmfmlhODV1E42aSkHGH3/8WsnUk10x8QzL1fjlb41 g269nicNxjfeMmYILD9h/5dnFjvX49qeQLipuYUQRo4ASY44a95p0wgG9Oa8Jn0O6j 9c6Kdxhit608YoiMrf5OfCrLr3SJveDOe59F7r/A= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727992AbgEPDnG (ORCPT ); Fri, 15 May 2020 23:43:06 -0400 Received: from mail.kernel.org ([198.145.29.99]:45792 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726247AbgEPDnF (ORCPT ); Fri, 15 May 2020 23:43:05 -0400 Received: from devnote2 (NE2965lan1.rev.em-net.ne.jp [210.141.244.193]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 773F320728; Sat, 16 May 2020 03:43:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589600585; bh=9Yr3NqlaT8J3yD/oIp4iOMhtlWnif5o5ocW4LHaILdM=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=gyBQnTy1kkqh/qqbQgXTvgoLZUb4vpkCq+qjNMxNfH2LO1uD/nFf2CQ93t2pqZ2HH Nvv3z8XinGroioseW6l362KaQNKI1k7UrzuUhEywWLMpAOhwLDsF/32qhs84qDVP/z cpTKthgjLlt17JXXUVZs8KirdFerSU19m7odBjKc= Date: Sat, 16 May 2020 12:42:59 +0900 From: Masami Hiramatsu To: Christoph Hellwig Cc: x86@kernel.org, Alexei Starovoitov , Daniel Borkmann , Linus Torvalds , Andrew Morton , linux-parisc@vger.kernel.org, linux-um@lists.infradead.org, netdev@vger.kernel.org, bpf@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 14/18] maccess: allow architectures to provide kernel probing directly Message-Id: <20200516124259.5b68a4e1d4670efa1397a1e0@kernel.org> In-Reply-To: <20200513160038.2482415-15-hch@lst.de> References: <20200513160038.2482415-1-hch@lst.de> <20200513160038.2482415-15-hch@lst.de> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.32; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Christoph, On Wed, 13 May 2020 18:00:34 +0200 Christoph Hellwig wrote: > Provide alternative versions of probe_kernel_read, probe_kernel_write > and strncpy_from_kernel_unsafe that don't need set_fs magic, but instead > use arch hooks that are modelled after unsafe_{get,put}_user to access > kernel memory in an exception safe way. This patch seems to introduce new implementation of probe_kernel_read/write() and strncpy_from_kernel_unsafe(), but also drops copy_from/to_kernel_nofault() and strncpy_from_kernel_nofault() if HAVE_ARCH_PROBE_KERNEL is defined. In the result, this cause a link error with BPF and kprobe events. BTW, what is the difference of *_unsafe() and *_nofault()? (maybe we make those to *_nofault() finally?) Thank you, > > Signed-off-by: Christoph Hellwig > --- > mm/maccess.c | 76 ++++++++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 76 insertions(+) > > diff --git a/mm/maccess.c b/mm/maccess.c > index 9773e2253b495..e9efe2f98e34a 100644 > --- a/mm/maccess.c > +++ b/mm/maccess.c > @@ -12,6 +12,81 @@ bool __weak probe_kernel_read_allowed(void *dst, const void *unsafe_src, > return true; > } > > +#ifdef HAVE_ARCH_PROBE_KERNEL > + > +#define probe_kernel_read_loop(dst, src, len, type, err_label) \ > + while (len >= sizeof(type)) { \ > + arch_kernel_read(dst, src, type, err_label); \ > + dst += sizeof(type); \ > + src += sizeof(type); \ > + len -= sizeof(type); \ > + } > + > +long probe_kernel_read(void *dst, const void *src, size_t size) > +{ > + if (!probe_kernel_read_allowed(dst, src, size)) > + return -EFAULT; > + > + pagefault_disable(); > + probe_kernel_read_loop(dst, src, size, u64, Efault); > + probe_kernel_read_loop(dst, src, size, u32, Efault); > + probe_kernel_read_loop(dst, src, size, u16, Efault); > + probe_kernel_read_loop(dst, src, size, u8, Efault); > + pagefault_enable(); > + return 0; > +Efault: > + pagefault_enable(); > + return -EFAULT; > +} > +EXPORT_SYMBOL_GPL(probe_kernel_read); > + > +#define probe_kernel_write_loop(dst, src, len, type, err_label) \ > + while (len >= sizeof(type)) { \ > + arch_kernel_write(dst, src, type, err_label); \ > + dst += sizeof(type); \ > + src += sizeof(type); \ > + len -= sizeof(type); \ > + } > + > +long probe_kernel_write(void *dst, const void *src, size_t size) > +{ > + pagefault_disable(); > + probe_kernel_write_loop(dst, src, size, u64, Efault); > + probe_kernel_write_loop(dst, src, size, u32, Efault); > + probe_kernel_write_loop(dst, src, size, u16, Efault); > + probe_kernel_write_loop(dst, src, size, u8, Efault); > + pagefault_enable(); > + return 0; > +Efault: > + pagefault_enable(); > + return -EFAULT; > +} > + > +long strncpy_from_kernel_unsafe(char *dst, const void *unsafe_addr, long count) > +{ > + const void *src = unsafe_addr; > + > + if (unlikely(count <= 0)) > + return 0; > + if (!probe_kernel_read_allowed(dst, unsafe_addr, count)) > + return -EFAULT; > + > + pagefault_disable(); > + do { > + arch_kernel_read(dst, src, u8, Efault); > + dst++; > + src++; > + } while (dst[-1] && src - unsafe_addr < count); > + pagefault_enable(); > + > + dst[-1] = '\0'; > + return src - unsafe_addr; > +Efault: > + pagefault_enable(); > + dst[-1] = '\0'; > + return -EFAULT; > +} > +#else /* HAVE_ARCH_PROBE_KERNEL */ > /** > * probe_kernel_read(): safely attempt to read from kernel-space > * @dst: pointer to the buffer that shall take the data > @@ -114,6 +189,7 @@ long strncpy_from_kernel_nofault(char *dst, const void *unsafe_addr, long count) > > return ret ? -EFAULT : src - unsafe_addr; > } > +#endif /* HAVE_ARCH_PROBE_KERNEL */ > > /** > * probe_user_read(): safely attempt to read from a user-space location > -- > 2.26.2 > -- Masami Hiramatsu