From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm1-f70.google.com (mail-wm1-f70.google.com [209.85.128.70]) by kanga.kvack.org (Postfix) with ESMTP id 13A0A6B6A57 for ; Mon, 3 Dec 2018 12:11:15 -0500 (EST) Received: by mail-wm1-f70.google.com with SMTP id t62-v6so4556513wmg.6 for ; Mon, 03 Dec 2018 09:11:15 -0800 (PST) Received: from pegase1.c-s.fr (pegase1.c-s.fr. [93.17.236.30]) by mx.google.com with ESMTPS id n4si6250693wmn.59.2018.12.03.09.11.13 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 03 Dec 2018 09:11:13 -0800 (PST) Subject: Re: [RFC PATCH] mm: add probe_user_read() and probe_user_address() References: <336eb81e62d6c683a69d312f533899dcb6bcf770.1539959864.git.christophe.leroy@c-s.fr> From: Christophe LEROY Message-ID: Date: Mon, 3 Dec 2018 18:11:11 +0100 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: fr Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org List-ID: To: Kees Cook Cc: Andrew Morton , Michael Ellerman , LKML , PowerPC , Linux-MM Le 19/10/2018 à 17:42, Kees Cook a écrit : > On Fri, Oct 19, 2018 at 8:14 AM, Christophe Leroy > wrote: >> In the powerpc, there are several places implementing safe >> access to user data. This is sometimes implemented using >> probe_kerne_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() and probe_kernel_address(), >> this patch adds probe_user_read() and probe_user_address(). >> >> probe_user_read() does the same as probe_kernel_read() but >> first checks that it is really a user address. >> >> probe_user_address() is a shortcut to probe_user_read() >> >> Signed-off-by: Christophe Leroy >> --- >> include/linux/uaccess.h | 10 ++++++++++ >> mm/maccess.c | 33 +++++++++++++++++++++++++++++++++ >> 2 files changed, 43 insertions(+) >> >> diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h >> index efe79c1cdd47..fb00e3f847d7 100644 >> --- a/include/linux/uaccess.h >> +++ b/include/linux/uaccess.h >> @@ -266,6 +266,16 @@ 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_address(): safely attempt to read from a user location >> + * @addr: address to read from >> + * @retval: read into this variable >> + * >> + * Returns 0 on success, or -EFAULT. >> + */ >> +#define probe_user_address(addr, retval) \ >> + probe_user_read(&(retval), addr, sizeof(retval)) >> + >> #ifndef user_access_begin >> #define user_access_begin() do { } while (0) >> #define user_access_end() do { } while (0) >> diff --git a/mm/maccess.c b/mm/maccess.c >> index ec00be51a24f..85d4a88a6917 100644 >> --- a/mm/maccess.c >> +++ b/mm/maccess.c >> @@ -67,6 +67,39 @@ long __probe_kernel_write(void *dst, const void *src, size_t size) >> EXPORT_SYMBOL_GPL(probe_kernel_write); >> >> /** >> + * 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 >> + * >> + * 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. >> + */ >> + >> +long __weak probe_user_read(void *dst, const void *src, size_t size) >> + __attribute__((alias("__probe_user_read"))); > > Let's use #defines to deal with per-arch aliases so we can keep the > inline I'm suggesting below... > >> + >> +long __probe_user_read(void *dst, const void __user *src, size_t size) > > Please make this __always_inline so the "size" variable can be > examined for const-ness by the check_object_size() in > __copy_from_user_inatomic(). Ok, I did as suggested in the patch I just sent. Would it be worth doing the same with the existing probe_kernel_read() and probe_kernel_write() ? Christophe > > -Kees >