From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm1-f72.google.com (mail-wm1-f72.google.com [209.85.128.72]) by kanga.kvack.org (Postfix) with ESMTP id D14208E0038 for ; Tue, 8 Jan 2019 16:11:53 -0500 (EST) Received: by mail-wm1-f72.google.com with SMTP id 129so1374464wmy.7 for ; Tue, 08 Jan 2019 13:11:53 -0800 (PST) Received: from pegase1.c-s.fr (pegase1.c-s.fr. [93.17.236.30]) by mx.google.com with ESMTPS id l12si41534421wrg.404.2019.01.08.13.11.52 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 08 Jan 2019 13:11:52 -0800 (PST) Subject: Re: [PATCH v2 1/2] mm: add probe_user_read() References: <0b0db24e18063076e9d9f4e376994af83da05456.1546932949.git.christophe.leroy@c-s.fr> <20190108114803.583f203b86d4a368ac9796f3@linux-foundation.org> From: Christophe Leroy Message-ID: <19c99d33-b796-72df-4212-20255f84efa0@c-s.fr> Date: Tue, 8 Jan 2019 22:11:50 +0100 MIME-Version: 1.0 In-Reply-To: <20190108114803.583f203b86d4a368ac9796f3@linux-foundation.org> 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: Andrew Morton Cc: Kees Cook , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , Mike Rapoport , linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org Le 08/01/2019 à 20:48, Andrew Morton a écrit : > On Tue, 8 Jan 2019 07:37:44 +0000 (UTC) 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. >> >> ... >> >> --- 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. >> + * >> + * 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 > > Why was the __always_inline needed? > > This function is pretty large. Why is it inlined? > Kees told to do that way, see https://patchwork.ozlabs.org/patch/986848/ Christophe