From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-yw1-f72.google.com (mail-yw1-f72.google.com [209.85.161.72]) by kanga.kvack.org (Postfix) with ESMTP id C4EB86B0007 for ; Fri, 19 Oct 2018 11:42:17 -0400 (EDT) Received: by mail-yw1-f72.google.com with SMTP id 123-v6so3304870ywt.12 for ; Fri, 19 Oct 2018 08:42:17 -0700 (PDT) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id x124-v6sor2929720ywa.149.2018.10.19.08.42.16 for (Google Transport Security); Fri, 19 Oct 2018 08:42:16 -0700 (PDT) Received: from mail-yw1-f43.google.com (mail-yw1-f43.google.com. [209.85.161.43]) by smtp.gmail.com with ESMTPSA id 200-v6sm5930819ywq.97.2018.10.19.08.42.14 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 19 Oct 2018 08:42:14 -0700 (PDT) Received: by mail-yw1-f43.google.com with SMTP id d126-v6so13355434ywa.5 for ; Fri, 19 Oct 2018 08:42:14 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <336eb81e62d6c683a69d312f533899dcb6bcf770.1539959864.git.christophe.leroy@c-s.fr> References: <336eb81e62d6c683a69d312f533899dcb6bcf770.1539959864.git.christophe.leroy@c-s.fr> From: Kees Cook Date: Fri, 19 Oct 2018 08:42:12 -0700 Message-ID: Subject: Re: [RFC PATCH] mm: add probe_user_read() and probe_user_address() Content-Type: text/plain; charset="UTF-8" Sender: owner-linux-mm@kvack.org List-ID: To: Christophe Leroy Cc: Andrew Morton , Michael Ellerman , LKML , PowerPC , Linux-MM 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(). -Kees -- Kees Cook Pixel Security