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[93.17.236.30]) by mx.google.com with ESMTPS id gi9-v6si4786273ejb.236.2019.01.07.23.37.46 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 07 Jan 2019 23:37:47 -0800 (PST) Received-SPF: pass (google.com: domain of christophe.leroy@c-s.fr designates 93.17.236.30 as permitted sender) client-ip=93.17.236.30; Authentication-Results: mx.google.com; spf=pass (google.com: domain of christophe.leroy@c-s.fr designates 93.17.236.30 as permitted sender) smtp.mailfrom=christophe.leroy@c-s.fr Received: from localhost (mailhub1-int [192.168.12.234]) by localhost (Postfix) with ESMTP id 43Ykcn4BkMz9txMg; Tue, 8 Jan 2019 08:37:45 +0100 (CET) X-Virus-Scanned: Debian amavisd-new at c-s.fr Received: from pegase1.c-s.fr ([192.168.12.234]) by localhost (pegase1.c-s.fr [192.168.12.234]) (amavisd-new, port 10024) with ESMTP id kvvQgho76Xec; Tue, 8 Jan 2019 08:37:45 +0100 (CET) Received: from messagerie.si.c-s.fr (messagerie.si.c-s.fr [192.168.25.192]) by pegase1.c-s.fr (Postfix) with ESMTP id 43Ykcn3f97z9txMf; Tue, 8 Jan 2019 08:37:45 +0100 (CET) Received: from localhost (localhost [127.0.0.1]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 688678B794; Tue, 8 Jan 2019 08:37:46 +0100 (CET) X-Virus-Scanned: amavisd-new at c-s.fr Received: from messagerie.si.c-s.fr ([127.0.0.1]) by localhost (messagerie.si.c-s.fr [127.0.0.1]) (amavisd-new, port 10023) with ESMTP id SbDgLRF0y1hn; Tue, 8 Jan 2019 08:37:46 +0100 (CET) Received: from po16846vm.idsi0.si.c-s.fr (unknown [192.168.4.90]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 3311B8B754; Tue, 8 Jan 2019 08:37:46 +0100 (CET) Received: by localhost.localdomain (Postfix, from userid 0) id 5FE5F69A7C; Tue, 8 Jan 2019 07:37:44 +0000 (UTC) Message-Id: <0b0db24e18063076e9d9f4e376994af83da05456.1546932949.git.christophe.leroy@c-s.fr> From: Christophe Leroy Subject: [PATCH v2 1/2] mm: add probe_user_read() To: Kees Cook , Andrew Morton , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , Mike Rapoport Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org Date: Tue, 8 Jan 2019 07:37:44 +0000 (UTC) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: X-Virus-Scanned: ClamAV using ClamSMTP 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. + * + * 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)