From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id EE04C34B1A3; Mon, 7 Sep 2026 11:00:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788778806; cv=none; b=g1ETXgxG6QZV3/3bQ0lm4hbHN+X7sKaDVjx6xes7iD05TBkep6ZIFd2BVciKpAi4QqivLGsbBhX95hRta5mIfVW/jlKdpaOBEsNSzoExXVu4w3r4DdLevsXG1IuOVzTO6ziqRDwRiZU0PFR41ZF6y2nS0VJfuiJ41kVQJfopX6k= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788778806; c=relaxed/simple; bh=7+s+Zh4RcjPvicJEVI/wOVutWzMDm1ld994AA8TUWDw=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ROfjxUP4nQAbzitviy1LAplZyF8PhuR0bGg0FjZsra5cPuSvNmnR/5QuRNxd/dlgU83GXzc+RX/gywwZvGokKwjqTIDYFjfofj/uJzVY3algdeIvlZmLHZS0JWURMNMqbXnBxW/0vAdFpWHNjvASoL7O5+2bQgB0gH6DAa1JFp4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=OS1bd8l5; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="OS1bd8l5" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DBF241F00A3A; Mon, 7 Sep 2026 10:59:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788778804; bh=ZmRAQp7CT9ZcGnXRbWq2cl8HArUYmjma0K0TpVSARi0=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=OS1bd8l53HBFTLeWpn+DLUZW6acFae8EN0TYc4g1vuJkfPuU9kXzmAUwy2G73YgMu 9IHR/D9kde7ZJvyI1/j+ddlfwpHOagprqjMcbn4V6AAmIrEXVKq8UvBDn7qYUVILek k/e6wBruu3DFLtXzN6AUY099s9O8sTOtqYhZjwG7TOU0d5UxZeYxCCOIlqlDop5lMC dmMA3yskAPtf8fg3NkoT2yvuEpHRlfW7Ex7wUaKR3pPcwFRI6USMASdXv78Mxj106o VjPROn9VYDQQC35JrwOlEi2ke9YQJlGFiD0p1RcmJSwgRpjS35fbAz09gMTykpyXTr 714lZ1wOpZxdw== Message-ID: <0e4edfd3-0c82-42e0-ad09-19ff8b8d1511@kernel.org> Date: Mon, 7 Sep 2026 12:59:57 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH bpf-next v4 1/7] mm: Add copy_remote_mm_str() To: Anastasios Papagiannis , bpf@vger.kernel.org Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, viro@zeniv.linux.org.uk, brauner@kernel.org, akpm@linux-foundation.org, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, eddyz87@gmail.com, memxor@gmail.com, kpsingh@kernel.org, matt@bobrowski.net, song@kernel.org, utilityemal77@gmail.com, sun.jian.kdev@gmail.com, "Lorenzo Stoakes (Arm)" References: <20260904145340.40212-1-tasos.papagiannnis@gmail.com> <20260904145340.40212-2-tasos.papagiannnis@gmail.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20260904145340.40212-2-tasos.papagiannnis@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit > diff --git a/mm/nommu.c b/mm/nommu.c > index ed3934bc2de4..94e3709e95fd 100644 > --- a/mm/nommu.c > +++ b/mm/nommu.c > @@ -1716,13 +1716,16 @@ EXPORT_SYMBOL_GPL(access_process_vm); > * Copy a string from another process's address space as given in mm. > * If there is any error return -EFAULT. > */ > -static int __copy_remote_vm_str(struct mm_struct *mm, unsigned long addr, > +static int __copy_remote_mm_str(struct mm_struct *mm, unsigned long addr, > void *buf, int len) > { > unsigned long addr_end; > struct vm_area_struct *vma; > int ret = -EFAULT; > > + if (unlikely(len == 0)) > + return 0; We have this check in copy_remote_vm_str(). Why are we performing the check now twice? It should either go only into __copy_remote_mm_str(), or if there a reason to have it before get_task_mm(), it should go into copy_remote_mm_str(). Same applies to the memory.c case. > + > *(char *)buf = '\0'; > > if (mmap_read_lock_killable(mm)) > @@ -1752,6 +1755,27 @@ static int __copy_remote_vm_str(struct mm_struct *mm, unsigned long addr, > return ret; > } > > +/** > + * copy_remote_mm_str - copy a string from a remote address space. > + * @mm: the remote address space > + * @addr: start address to read from > + * @buf: destination buffer > + * @len: number of bytes to copy > + * @gup_flags: flags modifying lookup behaviour (unused) > + * > + * The caller must hold a reference on @mm. > + * > + * Return: number of bytes copied from @addr (source) to @buf (destination), > + * not including the trailing NUL. If @len is zero, return 0 without accessing > + * @buf. Otherwise, @buf is always NUL-terminated. On any error, return > + * -EFAULT. > + */ > +int copy_remote_mm_str(struct mm_struct *mm, unsigned long addr, > + void *buf, int len, unsigned int gup_flags) > +{ > + return __copy_remote_mm_str(mm, addr, buf, len); > +} What's more annoying is that both implementations of copy_remote_vm_str() are identical, and both implementations of copy_remote_mm_str() are nearly identical (just dropping the gup_flags for nommu). I'd like to avoid duplicating code for nommu. If we could export __copy_remote_vm_str(mm, addr, buf, len, gup_flags) for both cases, we could instead provide a single implementation for copy_remote_vm_str() and copy_remote_mm_str() e.g., in mm.h? (I'd prefer somewhere else, but we don't seem to have a good git for memory.c + nommu.c shared stuff) Now, that's also not completely nice, as I don't want us to EXPORT __copy_remote_vm_str() ... given that these functions are "#ifdef CONFIG_BPF_SYSCALL" could we EXPORT_SYMBOL_FOR_MODULES? Just a thought. CCing Lorenzo. -- Cheers, David