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 B6C2F26FDAD; Fri, 18 Apr 2025 09:03:30 +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=1744967013; cv=none; b=pwFyS1yj1UuVI+7ZoewvvaMow/rAXjFvWBLpZyd2WxB7oiYw3OFZPFGoXLs2E/X4aljOvP2WvhatJfnrc/JDSfWF36qdDnMKyd9JngBUDOEb7cXSJI8dcbRwJULrzF0ethtgt4Y1WNNs4Ntn5EzAtJ4J72KIt68ilumG7pVszZE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744967013; c=relaxed/simple; bh=ux85UaKGHmWgF6HhVM8OOvobqVgJwNDXi1I9R0gjp8o=; h=Message-ID:Date:MIME-Version:Subject:From:To:Cc:References: In-Reply-To:Content-Type; b=dKLYu3Ngo+bwlWaswMPtY0s82DUuQk4E5UsK1aML/r27rJQ+G8LXdh8y3VFKI2AO0BkKJTLuAVGfx5xSRGwPn8zpvOKqkqiY6tgXk7aOuUystxa2UHYPMhg3Wv1YK2uxaveuKfRIGAtJQjfx77QMHYhMxI0qoxtbTFXC/WaEt/E= 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=OaH6t4Em; 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="OaH6t4Em" 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:References: Cc:To:From: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=/TUgmXRIt862ZvkLN+SJfvXp8pRPa3ExVWG6heV/r3c=; b=OaH6t4EmRnkaOCLDxBbVCkP9bZ r0Nae3ODBz1Bym6pu799K8rcBPxqn1Y29idZLKhw5eCeZn+pSTjbdmdr6gZ+QVApzEjGcJWA0jEzl 4AE+wkHEn0WcMeN4Kqjlf+wth7LVvp+b+RwIYtilGDIwhk9qfCaKWt+9b7DiKs1YBDHh+wJFPc9VD 0TN0yz+TmMdAa02YBXKaVi8t/tZlodlb++fqvdz/q5Isg9pLu8VtoD8SSWEavvWOXF0QhpG3vB2bx sZzabt9Q0i9JO5uQQgWBShk3OAl4nz0a88Nks/wpQaV11tJ+VnBe7WqINPam5jkBbMY7xh7G2BA2F vrobwNEQ==; Received: from 39-14-33-89.adsl.fetnet.net ([39.14.33.89] helo=[192.168.220.43]) by fanzine2.igalia.com with esmtpsa (Cipher TLS1.3:ECDHE_X25519__RSA_PSS_RSAE_SHA256__AES_128_GCM:128) (Exim) id 1u5hd0-001AZP-2j; Fri, 18 Apr 2025 11:03:18 +0200 Message-ID: <983ba47e-ab95-4a43-bca2-97b75c3c90d0@igalia.com> Date: Fri, 18 Apr 2025 17:03:09 +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 From: Gavin Guo To: ziy@nvidia.com Cc: david@redhat.com, willy@infradead.org, linmiaohe@huawei.com, hughd@google.com, revest@google.com, kernel-dev@igalia.com, linux-kernel@vger.kernel.org, stable@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org References: <20250418085802.2973519-1-gavinguo@igalia.com> Content-Language: en-US In-Reply-To: <20250418085802.2973519-1-gavinguo@igalia.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 4/18/25 16:58, 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(-) > > 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; > + } > __split_huge_pmd_locked(vma, pmd, address, freeze); > } > } > > base-commit: a24588245776dafc227243a01bfbeb8a59bafba9 Hi Zi, I've carefully reviewed the mailing list and observed that the indentation is not a strong concern from the reviews. And the cleanup suggestion from David will override the modification in this patch. I have decided to keep the original version (the unindented one). Let me know if you have any feedback with the v2 patch. Thank you!