From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 38D3A524D7; Mon, 11 Dec 2023 18:33:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="GbyPbSzv" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B33FCC433C9; Mon, 11 Dec 2023 18:33:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1702319611; bh=cTF2GC+9aIFqD+6nB1EdY1Y6Qv+aPoLR8EYrpXfENq0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=GbyPbSzvz5975Se0ft76Hu7bM36LyjtPQ6ZUt56B2/oI66pHjQv1i0IllBJwnZSvA +5dfZ+Kwh+n3QaiAkiZ2YL6GAMK4DrQkLoXlnqSaHMsj6kIu2fdn8uPUUqi4OdkCnH ZYnWIG1Un2psubJv8Lr7UE/yIR9zkK/1ARwDdZr0= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Hugh Dickins , David Hildenbrand , =?UTF-8?q?Jos=C3=A9=20Pekkarinen?= , "Kirill A. Shutemov" , "Matthew Wilcox (Oracle)" , Andrew Morton , syzbot+89edd67979b52675ddec@syzkaller.appspotmail.com, Jann Horn Subject: [PATCH 6.6 168/244] mm: fix oops when filemap_map_pmd() without prealloc_pte Date: Mon, 11 Dec 2023 19:21:01 +0100 Message-ID: <20231211182053.417228446@linuxfoundation.org> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20231211182045.784881756@linuxfoundation.org> References: <20231211182045.784881756@linuxfoundation.org> User-Agent: quilt/0.67 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Hugh Dickins commit 9aa1345d66b8132745ffb99b348b1492088da9e2 upstream. syzbot reports oops in lockdep's __lock_acquire(), called from __pte_offset_map_lock() called from filemap_map_pages(); or when I run the repro, the oops comes in pmd_install(), called from filemap_map_pmd() called from filemap_map_pages(), just before the __pte_offset_map_lock(). The problem is that filemap_map_pmd() has been assuming that when it finds pmd_none(), a page table has already been prepared in prealloc_pte; and indeed do_fault_around() has been careful to preallocate one there, when it finds pmd_none(): but what if *pmd became none in between? My 6.6 mods in mm/khugepaged.c, avoiding mmap_lock for write, have made it easy for *pmd to be cleared while servicing a page fault; but even before those, a huge *pmd might be zapped while a fault is serviced. The difference in symptomatic stack traces comes from the "memory model" in use: pmd_install() uses pmd_populate() uses page_to_pfn(): in some models that is strict, and will oops on the NULL prealloc_pte; in other models, it will construct a bogus value to be populated into *pmd, then __pte_offset_map_lock() oops when trying to access split ptlock pointer (or some other symptom in normal case of ptlock embedded not pointer). Link: https://lore.kernel.org/linux-mm/20231115065506.19780-1-jose.pekkarinen@foxhound.fi/ Link: https://lkml.kernel.org/r/6ed0c50c-78ef-0719-b3c5-60c0c010431c@google.com Fixes: f9ce0be71d1f ("mm: Cleanup faultaround and finish_fault() codepaths") Signed-off-by: Hugh Dickins Reported-and-tested-by: syzbot+89edd67979b52675ddec@syzkaller.appspotmail.com Closes: https://lore.kernel.org/linux-mm/0000000000005e44550608a0806c@google.com/ Reviewed-by: David Hildenbrand Cc: Jann Horn , Cc: José Pekkarinen Cc: Kirill A. Shutemov Cc: Matthew Wilcox (Oracle) Cc: [5.12+] Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman --- mm/filemap.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/mm/filemap.c +++ b/mm/filemap.c @@ -3422,7 +3422,7 @@ static bool filemap_map_pmd(struct vm_fa } } - if (pmd_none(*vmf->pmd)) + if (pmd_none(*vmf->pmd) && vmf->prealloc_pte) pmd_install(mm, vmf->pmd, &vmf->prealloc_pte); return false;