From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from fanzine2.igalia.com (fanzine.igalia.com [178.60.130.6]) (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 E7250126C1E; Mon, 21 Apr 2025 14:48:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=178.60.130.6 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745246909; cv=none; b=AHpcatf+/UHFEBD5/f7kJuL9Ls4x/eOXg3u0XPQowFUudlcV9GqzQaiLH8rOH5gca8GJZyBg4UE2w/wX392f7XXvkswv+d/bJDHe8+UpuFyKO6RMknfVynnc0uilGTG31N7cPwxn9VMU5xy8eZC2BxkBeeHjx7n5OuYTY6GUmyY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745246909; c=relaxed/simple; bh=7aAMJZ+iym1p8+ko8GobuLt++Nib0/HQSbNLT3Cv0QE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=HJlG+5HFnWA+GjMgeBn3UHEnxgGgXSEz6COZVjR8hl/7pu/p3StN3kjRJQjpwxx2v4vXbkx1EXHK4Z50iwhNUSm21y5dA710hD5gbU4vMqR59rBpj/B3wlu7tui4+vlqSDk01PHC4+mQzNSd1YL9C6l7Ayk56R38QqNsSGJY60A= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=igalia.com; spf=pass smtp.mailfrom=igalia.com; dkim=pass (2048-bit key) header.d=igalia.com header.i=@igalia.com header.b=NvnrrWqB; arc=none smtp.client-ip=178.60.130.6 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=igalia.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=igalia.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=igalia.com header.i=@igalia.com header.b="NvnrrWqB" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=igalia.com; s=20170329; h=Content-Transfer-Encoding:Content-Type:In-Reply-To:From: References:Cc:To:Subject:MIME-Version:Date:Message-ID:Sender:Reply-To: Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender: Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help:List-Unsubscribe: List-Subscribe:List-Post:List-Owner:List-Archive; bh=kwVVw2CqIRRe0Myaq1Inek1FYVeiqCcyjpy3VoSZ7XY=; b=NvnrrWqB8J2UENYzRduUt5rh6M HGubS1PYlulbA5D5rAiOfo5eEOVjSt0k0FezS2GHeKNRMQG+Q/qT36/9PFNAPYRGKgesNiduV+q8U dHbX9zEbmfh3b76m2sOvd9WaroSythbTkir+oi8DcbJBSA+djJb/IwbjJ7ZdUMgdcs89+/g03spFO op/X/nag1CXf9JVZYWjltWttrSKsRdhd6pukWfNDSrzTrzk8O+ukOtZwVOdJMfQX5wyCqZaUE5HLU JCp3piW6Z0xrJ7XnJjol2mYYwBqcAK193GBTIWr0eF50Znfrhs2NIbD8rV2ESfB379bx0AA2JSpWa N5u9F5PQ==; Received: from 114-44-233-154.dynamic-ip.hinet.net ([114.44.233.154] helo=[192.168.1.104]) by fanzine2.igalia.com with esmtpsa (Cipher TLS1.3:ECDHE_X25519__RSA_PSS_RSAE_SHA256__AES_128_GCM:128) (Exim) id 1u6sRA-0060Jw-Ve; Mon, 21 Apr 2025 16:47:57 +0200 Message-ID: Date: Mon, 21 Apr 2025 22:47:50 +0800 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 v2] mm/huge_memory: fix dereferencing invalid pmd migration entry To: Gavin Shan , David Hildenbrand , linux-mm@kvack.org, akpm@linux-foundation.org Cc: willy@infradead.org, ziy@nvidia.com, linmiaohe@huawei.com, hughd@google.com, revest@google.com, kernel-dev@igalia.com, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20250418085802.2973519-1-gavinguo@igalia.com> Content-Language: en-US From: Gavin Guo In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 4/19/25 07:53, Gavin Shan wrote: > Hi Gavin, > > On 4/18/25 8:42 PM, David Hildenbrand wrote: >> On 18.04.25 10:58, Gavin Guo wrote: >>> When migrating a THP, concurrent access to the PMD migration entry >>> during a deferred split scan can lead to a invalid address access, as >>> illustrated below. To prevent this page fault, it is necessary to check >>> the PMD migration entry and return early. In this context, there is no >>> need to use pmd_to_swp_entry and pfn_swap_entry_to_page to verify the >>> equality of the target folio. Since the PMD migration entry is locked, >>> it cannot be served as the target. >>> >>> Mailing list discussion and explanation from Hugh Dickins: >>> "An anon_vma lookup points to a location which may contain the folio of >>> interest, but might instead contain another folio: and weeding out those >>> other folios is precisely what the "folio != pmd_folio((*pmd)" check >>> (and the "risk of replacing the wrong folio" comment a few lines above >>> it) is for." >>> >>> BUG: unable to handle page fault for address: ffffea60001db008 >>> CPU: 0 UID: 0 PID: 2199114 Comm: tee Not tainted 6.14.0+ #4 NONE >>> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3- >>> debian-1.16.3-2 04/01/2014 >>> RIP: 0010:split_huge_pmd_locked+0x3b5/0x2b60 >>> Call Trace: >>> >>> try_to_migrate_one+0x28c/0x3730 >>> rmap_walk_anon+0x4f6/0x770 >>> unmap_folio+0x196/0x1f0 >>> split_huge_page_to_list_to_order+0x9f6/0x1560 >>> deferred_split_scan+0xac5/0x12a0 >>> shrinker_debugfs_scan_write+0x376/0x470 >>> full_proxy_write+0x15c/0x220 >>> vfs_write+0x2fc/0xcb0 >>> ksys_write+0x146/0x250 >>> do_syscall_64+0x6a/0x120 >>> entry_SYSCALL_64_after_hwframe+0x76/0x7e >>> >>> The bug is found by syzkaller on an internal kernel, then confirmed on >>> upstream. >>> >>> Fixes: 84c3fc4e9c56 ("mm: thp: check pmd migration entry in common >>> path") >>> Cc: stable@vger.kernel.org >>> Signed-off-by: Gavin Guo >>> Acked-by: David Hildenbrand >>> Acked-by: Hugh Dickins >>> Acked-by: Zi Yan >>> Link: https://lore.kernel.org/all/20250414072737.1698513-1- >>> gavinguo@igalia.com/ >>> --- >>> V1 -> V2: Add explanation from Hugh and correct the wording from page >>> fault to invalid address access. >>> >>>   mm/huge_memory.c | 18 ++++++++++++++---- >>>   1 file changed, 14 insertions(+), 4 deletions(-) >>> > > Reviewed-by: Gavin Shan > >>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >>> index 2a47682d1ab7..0cb9547dcff2 100644 >>> --- a/mm/huge_memory.c >>> +++ b/mm/huge_memory.c >>> @@ -3075,6 +3075,8 @@ static void __split_huge_pmd_locked(struct >>> vm_area_struct *vma, pmd_t *pmd, >>>   void split_huge_pmd_locked(struct vm_area_struct *vma, unsigned >>> long address, >>>                  pmd_t *pmd, bool freeze, struct folio *folio) >>>   { >>> +    bool pmd_migration = is_pmd_migration_entry(*pmd); >>> + >>>       VM_WARN_ON_ONCE(folio && !folio_test_pmd_mappable(folio)); >>>       VM_WARN_ON_ONCE(!IS_ALIGNED(address, HPAGE_PMD_SIZE)); >>>       VM_WARN_ON_ONCE(folio && !folio_test_locked(folio)); >>> @@ -3085,10 +3087,18 @@ void split_huge_pmd_locked(struct >>> vm_area_struct *vma, unsigned long address, >>>        * require a folio to check the PMD against. Otherwise, there >>>        * is a risk of replacing the wrong folio. >>>        */ >>> -    if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd) || >>> -        is_pmd_migration_entry(*pmd)) { >>> -        if (folio && folio != pmd_folio(*pmd)) >>> -            return; >>> +    if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd) || pmd_migration) { >>> +        if (folio) { >>> +            /* >>> +             * Do not apply pmd_folio() to a migration entry; and >>> +             * folio lock guarantees that it must be of the wrong >>> +             * folio anyway. >>> +             */ >>> +            if (pmd_migration) >>> +                return; >>> +            if (folio != pmd_folio(*pmd)) >>> +                return; >> >> Nit: just re-reading, I would have simply done >> >> if (pmd_migration || folio != pmd_folio(*pmd) >>      return; >> >> Anyway, this will hopefully get cleaned up soon either way, so I don't >> particularly mind. :) >> > > If v3 is needed to fix Zi's comments (commit log improvement), it can be > improved > slightly based on David's suggestion, to avoid another nested if > statement. Otherwise, > it's fine since it needs to be cleaned up soon. > >     /* >      * Do not apply pmd_folio() to a migration entry, and folio lock >      * guarantees that it must be of the wrong folio anyway. >      */ >     if (folio && (pmd_migration || folio != pmd_filio(*pmd)) >         return; > > Thanks, > Gavin > > Gavin, thank you for the review as well. I submitted v3 including your suggestion with David's indentation idea and Zi's commit log fix.