From patchwork Mon Dec 19 16:30:13 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Hildenbrand X-Patchwork-Id: 13076860 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5A372C4332F for ; Mon, 19 Dec 2022 16:31:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232174AbiLSQbc (ORCPT ); Mon, 19 Dec 2022 11:31:32 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59052 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232224AbiLSQbW (ORCPT ); Mon, 19 Dec 2022 11:31:22 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 57A9512615 for ; Mon, 19 Dec 2022 08:30:37 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1671467435; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=iqzZDJr3eUwayKjs/1xitM2q4nRywOPqCiXpKwUBAdY=; b=BLzl9FTy/0Fg3iLnw02HZfxyjCJwivNsZWPArsQqwiiwoU5QcAENZIIj4nEWPXYAFr1CkF 3UjwiUj/Fjihd/JafANO6+ETQnzWe+yWTEY4YaMKNgEiap+fNWwYstpbwNvQiMFbM94Ll0 xbLYo87OsvQDqTdMHbctdJok3iZw6ME= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-332-UNsY6G-3NzygpiX6OJ2yDw-1; Mon, 19 Dec 2022 11:30:29 -0500 X-MC-Unique: UNsY6G-3NzygpiX6OJ2yDw-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 0F8D21991C41; Mon, 19 Dec 2022 16:30:26 +0000 (UTC) Received: from t480s.redhat.com (unknown [10.39.194.120]) by smtp.corp.redhat.com (Postfix) with ESMTP id 202D340C1073; Mon, 19 Dec 2022 16:30:22 +0000 (UTC) From: David Hildenbrand To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, io-uring@vger.kernel.org, David Hildenbrand , Linus Torvalds , Andrew Morton , Arnd Bergmann , Greg Kroah-Hartman , Nicolas Pitre , Jens Axboe , Pavel Begunkov Subject: [PATCH mm-stable RFC 2/2] mm/nommu: don't use VM_MAYSHARE for MAP_PRIVATE mappings Date: Mon, 19 Dec 2022 17:30:13 +0100 Message-Id: <20221219163013.259423-3-david@redhat.com> In-Reply-To: <20221219163013.259423-1-david@redhat.com> References: <20221219163013.259423-1-david@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.2 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Let's stop using VM_MAYSHARE for MAP_PRIVATE mappings and use VM_MAYOVERLAY instead. Rewrite determine_vm_flags() to make the whole logic easier to digest, and to cleanly separate MAP_PRIVATE vs. MAP_SHARED. No functional change intended. Signed-off-by: David Hildenbrand --- include/linux/mm.h | 7 ++++++- mm/nommu.c | 51 +++++++++++++++++++++++++++------------------- 2 files changed, 36 insertions(+), 22 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index 734d0bc7c7c6..c229eee6211c 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -276,7 +276,12 @@ extern unsigned int kobjsize(const void *objp); #define VM_MAYSHARE 0x00000080 #define VM_GROWSDOWN 0x00000100 /* general info on the segment */ +#ifdef CONFIG_MMU #define VM_UFFD_MISSING 0x00000200 /* missing pages tracking */ +#else /* CONFIG_MMU */ +#define VM_MAYOVERLAY 0x00000200 /* nommu: R/O MAP_PRIVATE mapping that might overlay a file mapping */ +#define VM_UFFD_MISSING 0 +#endif /* CONFIG_MMU */ #define VM_PFNMAP 0x00000400 /* Page-ranges managed without "struct page", just pure PFN */ #define VM_UFFD_WP 0x00001000 /* wrprotect pages tracking */ @@ -1374,7 +1379,7 @@ static inline bool is_nommu_shared_mapping(vm_flags_t flags) * ptrace does not apply. Note that there is no mprotect() to upgrade * write permissions later. */ - return flags & VM_MAYSHARE; + return flags & (VM_MAYSHARE | VM_MAYOVERLAY); } #endif diff --git a/mm/nommu.c b/mm/nommu.c index 6c4bdc07a776..5c628c868648 100644 --- a/mm/nommu.c +++ b/mm/nommu.c @@ -892,29 +892,36 @@ static unsigned long determine_vm_flags(struct file *file, unsigned long vm_flags; vm_flags = calc_vm_prot_bits(prot, 0) | calc_vm_flag_bits(flags); - /* vm_flags |= mm->def_flags; */ - if (!(capabilities & NOMMU_MAP_DIRECT)) { - /* attempt to share read-only copies of mapped file chunks */ + if (!file) { + /* + * MAP_ANONYMOUS. MAP_SHARED is mapped to MAP_PRIVATE, because + * there is no fork(). + */ vm_flags |= VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC; - if (file && !(prot & PROT_WRITE)) - vm_flags |= VM_MAYSHARE; + } else if (flags & MAP_PRIVATE) { + /* MAP_PRIVATE file mapping */ + if (capabilities & NOMMU_MAP_DIRECT) + vm_flags |= (capabilities & NOMMU_VMFLAGS); + else + vm_flags |= VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC; + + if (!(prot & PROT_WRITE) && !current->ptrace) + /* + * R/O private file mapping which cannot be used to + * modify memory, especially also not via active ptrace + * (e.g., set breakpoints) or later by upgrading + * permissions (no mprotect()). We can try overlaying + * the file mapping, which will work e.g., on chardevs, + * ramfs/tmpfs/shmfs and romfs/cramf. + */ + vm_flags |= VM_MAYOVERLAY; } else { - /* overlay a shareable mapping on the backing device or inode - * if possible - used for chardevs, ramfs/tmpfs/shmfs and - * romfs/cramfs */ - vm_flags |= VM_MAYSHARE | (capabilities & NOMMU_VMFLAGS); - if (flags & MAP_SHARED) - vm_flags |= VM_SHARED; + /* MAP_SHARED file mapping: NOMMU_MAP_DIRECT is set. */ + vm_flags |= VM_SHARED | VM_MAYSHARE | + (capabilities & NOMMU_VMFLAGS); } - /* refuse to let anyone share private mappings with this process if - * it's being traced - otherwise breakpoints set in it may interfere - * with another untraced process - */ - if ((flags & MAP_PRIVATE) && current->ptrace) - vm_flags &= ~VM_MAYSHARE; - return vm_flags; } @@ -952,9 +959,11 @@ static int do_mmap_private(struct vm_area_struct *vma, void *base; int ret, order; - /* invoke the file's mapping function so that it can keep track of - * shared mappings on devices or memory - * - VM_MAYSHARE will be set if it may attempt to share + /* + * Invoke the file's mapping function so that it can keep track of + * shared mappings on devices or memory. VM_MAYOVERLAY will be set if + * it may attempt to share, which will make is_nommu_shared_mapping() + * happy. */ if (capabilities & NOMMU_MAP_DIRECT) { ret = call_mmap(vma->vm_file, vma);