From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf1-f200.google.com (mail-pf1-f200.google.com [209.85.210.200]) by kanga.kvack.org (Postfix) with ESMTP id 1F68B8E0038 for ; Tue, 8 Jan 2019 02:51:15 -0500 (EST) Received: by mail-pf1-f200.google.com with SMTP id x67so2155089pfk.16 for ; Mon, 07 Jan 2019 23:51:15 -0800 (PST) Received: from mx0a-001b2d01.pphosted.com (mx0a-001b2d01.pphosted.com. [148.163.156.1]) by mx.google.com with ESMTPS id u4si54983024pga.91.2019.01.07.23.51.13 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 07 Jan 2019 23:51:13 -0800 (PST) Received: from pps.filterd (m0098393.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id x087nHqK108984 for ; Tue, 8 Jan 2019 02:51:13 -0500 Received: from e06smtp01.uk.ibm.com (e06smtp01.uk.ibm.com [195.75.94.97]) by mx0a-001b2d01.pphosted.com with ESMTP id 2pvpcmm90f-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Tue, 08 Jan 2019 02:51:13 -0500 Received: from localhost by e06smtp01.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 8 Jan 2019 07:51:10 -0000 Date: Tue, 8 Jan 2019 09:51:04 +0200 From: Mike Rapoport Subject: Re: [PATCH v2 1/2] mm: add probe_user_read() References: <0b0db24e18063076e9d9f4e376994af83da05456.1546932949.git.christophe.leroy@c-s.fr> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0b0db24e18063076e9d9f4e376994af83da05456.1546932949.git.christophe.leroy@c-s.fr> Message-Id: <20190108075104.GA4396@rapoport-lnx> Sender: owner-linux-mm@kvack.org List-ID: To: Christophe Leroy Cc: Kees Cook , Andrew Morton , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org On Tue, Jan 08, 2019 at 07:37:44AM +0000, Christophe Leroy wrote: > In powerpc code, there are several places implementing safe > access to user data. This is sometimes implemented using > probe_kernel_address() with additional access_ok() verification, > sometimes with get_user() enclosed in a pagefault_disable()/enable() > pair, etc. : > show_user_instructions() > bad_stack_expansion() > p9_hmi_special_emu() > fsl_pci_mcheck_exception() > read_user_stack_64() > read_user_stack_32() on PPC64 > read_user_stack_32() on PPC32 > power_pmu_bhrb_to() > > In the same spirit as probe_kernel_read(), this patch adds > probe_user_read(). > > probe_user_read() does the same as probe_kernel_read() but > first checks that it is really a user address. > > Signed-off-by: Christophe Leroy > --- > v2: Added "Returns:" comment and removed probe_user_address() > > Changes since RFC: Made a static inline function instead of weak function as recommended by Kees. > > include/linux/uaccess.h | 34 ++++++++++++++++++++++++++++++++++ > 1 file changed, 34 insertions(+) > > diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h > index 37b226e8df13..07f4f0ed69bc 100644 > --- a/include/linux/uaccess.h > +++ b/include/linux/uaccess.h > @@ -263,6 +263,40 @@ extern long strncpy_from_unsafe(char *dst, const void *unsafe_addr, long count); > #define probe_kernel_address(addr, retval) \ > probe_kernel_read(&retval, addr, sizeof(retval)) > > +/** > + * probe_user_read(): safely attempt to read from a user location > + * @dst: pointer to the buffer that shall take the data > + * @src: address to read from > + * @size: size of the data chunk > + * > + * Returns: 0 on success, -EFAULT on error. Nit: please put the "Returns:" comment after the description, otherwise kernel-doc considers it a part of the elaborate description. > + * > + * Safely read from address @src to the buffer at @dst. If a kernel fault > + * happens, handle that and return -EFAULT. > + * > + * We ensure that the copy_from_user is executed in atomic context so that > + * do_page_fault() doesn't attempt to take mmap_sem. This makes > + * probe_user_read() suitable for use within regions where the caller > + * already holds mmap_sem, or other locks which nest inside mmap_sem. > + */ > + > +#ifndef probe_user_read > +static __always_inline long probe_user_read(void *dst, const void __user *src, > + size_t size) > +{ > + long ret; > + > + if (!access_ok(src, size)) > + return -EFAULT; > + > + pagefault_disable(); > + ret = __copy_from_user_inatomic(dst, src, size); > + pagefault_enable(); > + > + return ret ? -EFAULT : 0; > +} > +#endif > + > #ifndef user_access_begin > #define user_access_begin(ptr,len) access_ok(ptr, len) > #define user_access_end() do { } while (0) > -- > 2.13.3 > -- Sincerely yours, Mike.