From nobody Sun Feb 8 01:33:54 2026 Received: from mail-ot1-f69.google.com (mail-ot1-f69.google.com [209.85.210.69]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 30F2123D2B4 for ; Mon, 2 Feb 2026 08:34:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.210.69 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770021289; cv=none; b=A3B1XfLMD3rRXDVAyl9J8Br1+6T1/wJu/N2DzbxquhYUtkcpCPFM6ykwnmMgmRovEtaZy7NPfDZScE2RovkiYnNJi410vozYSQy4r49sat/0vVP4zPSVHBdiR1/nkFsmhajdq4Oe3M2XFWgbs9zeYlgGYPg+6+W0zOwrnqxAIKA= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770021289; c=relaxed/simple; bh=F3o7bz0XakS13OqTS6ppWIW/wgftTxicIMOguwnx8ic=; h=MIME-Version:Date:In-Reply-To:Message-ID:Subject:From:To: Content-Type; b=LHlJHxMQeh62AxlsYQneR9mGVdAHM64RzgunTvBHBSESk5TT2qnFtGrxWZJUT/AHTc5V6HHHY1+XcauaVAv0OGJF21sUGlyJGdrLsnYEwqmNfM9UaFtJ9FJpxamCEgogkX7a6ptkE4HBVBDxzuLizryGT/PniK74nOr/OzK8XHw= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=syzkaller.appspotmail.com; spf=pass smtp.mailfrom=M3KW2WVRGUFZ5GODRSRYTGD7.apphosting.bounces.google.com; arc=none smtp.client-ip=209.85.210.69 Authentication-Results: smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=syzkaller.appspotmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=M3KW2WVRGUFZ5GODRSRYTGD7.apphosting.bounces.google.com Received: by mail-ot1-f69.google.com with SMTP id 46e09a7af769-7d195fe3eb4so17467704a34.3 for ; Mon, 02 Feb 2026 00:34:47 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1770021287; x=1770626087; h=to:from:subject:message-id:in-reply-to:date:mime-version :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=AEW7fe3yuqLuF0WtOncPfGe9mAKcJnK/sp2FDLN3Edk=; b=dMks9kTE0a5oqjtTXZVgu40zrXd/gmPJ2nC6zEAN0OMv+pByEI/gKypWkPvaxSfOxV Lqe/KllO9ehNoUP7HsQaeb2jA1/pPcJnTQxAxsw7n8KQjOkjUKeZKNZYsP4xeqNNj0Jz nT+ZghFy+XdjCVMni7yYCujaIJfb6DhsE4NLajcdNMFJXTNcIUDDd761DmiezXQ/0HlB ys/vlWq9Ca2ObaodzzfFDp3AzFW0LSobODWnwFtq9GRYyN1w1U5FlLIZ/kLtPFjstTRi CG16rim92uj1CoHj4LFbUBgHJBCNXCHmlxqoFhskrUdQshVLWMTHGXezRqob6LymUke+ rPFA== X-Gm-Message-State: AOJu0Yx8D7h4zNugeJDL7n7VDtw55ve/CyllIdg11R/5GlWedHo4CsjS XVQzH2u3gVCcEssHvhhDXzjyKGBVAGfimgIXLJzUr2qF/b1s2ULUhH6R15tnh3HQa1wS9ambSP2 myMF3jugtuARInZ+VJY1JJwc+QVCQMbn9NbMZlBunoXv+gIY1YBbXnKk5Hm0= Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Received: by 2002:a05:6820:3092:b0:663:e8d:ceb with SMTP id 006d021491bc7-6630f384e90mr4654139eaf.47.1770021287143; Mon, 02 Feb 2026 00:34:47 -0800 (PST) Date: Mon, 02 Feb 2026 00:34:47 -0800 In-Reply-To: <697d115a.050a0220.1d61ec.0004.GAE@google.com> X-Google-Appengine-App-Id: s~syzkaller X-Google-Appengine-App-Id-Alias: syzkaller Message-ID: <698061a7.050a0220.1d0a41.0028.GAE@google.com> Subject: Forwarded: [PATCH] KVM: guest_memfd: Reject large folios until support is implemented From: syzbot To: linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" For archival purposes, forwarding an incoming command email to linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com. *** Subject: [PATCH] KVM: guest_memfd: Reject large folios until support is imp= lemented Author: kartikey406@gmail.com #syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git= master Large folios are not yet supported in guest_memfd (see TODO comment in kvm_gmem_get_folio()), but can still be allocated if userspace uses madvise(MADV_HUGEPAGE), which overrides the folio order restrictions set by mapping_set_folio_order_range(). When a large folio is allocated, it triggers WARN_ON_ONCE() at line 416 in kvm_gmem_fault_user_mapping(), causing a kernel panic if panic_on_warn is enabled. Add mapping_set_folio_order_range(0, 0) as defense in depth, and actively check for large folios in kvm_gmem_get_folio(). If found, remove the large folio from the page cache and return -E2BIG to force reallocation as an order-0 page. This prevents the WARNING from triggering and avoids kernel panics. Reported-by: syzbot+33a04338019ac7e43a44@syzkaller.appspotmail.com Signed-off-by: Deepanshu Kartikey --- virt/kvm/guest_memfd.c | 20 +++++++++++++++++++- 1 file changed, 19 insertions(+), 1 deletion(-) diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c index fdaea3422c30..60181efdc00a 100644 --- a/virt/kvm/guest_memfd.c +++ b/virt/kvm/guest_memfd.c @@ -143,13 +143,30 @@ static struct folio *kvm_gmem_get_folio(struct inode = *inode, pgoff_t index) folio =3D __filemap_get_folio(inode->i_mapping, index, FGP_LOCK | FGP_ACCESSED, 0); if (!IS_ERR(folio)) - return folio; + goto check_folio; =20 policy =3D mpol_shared_policy_lookup(&GMEM_I(inode)->policy, index); folio =3D __filemap_get_folio_mpol(inode->i_mapping, index, FGP_LOCK | FGP_ACCESSED | FGP_CREAT, mapping_gfp_mask(inode->i_mapping), policy); mpol_cond_put(policy); + if (IS_ERR(folio)) + return folio;=20 +check_folio: + /* + * Large folios are not supported yet. This can still happen + * despite mapping_set_folio_order_range() if userspace uses + * madvise(MADV_HUGEPAGE) which can override the folio order + * restrictions. Reject the large folio and remove it from + * the page cache so the next fault can allocate a order-0 + * page instead. + */ + if (folio_test_large(folio)) { + folio_unlock(folio); + filemap_remove_folio(folio); + folio_put(folio); + return ERR_PTR(-E2BIG); + } =20 return folio; } @@ -596,6 +613,7 @@ static int __kvm_gmem_create(struct kvm *kvm, loff_t si= ze, u64 flags) inode->i_mode |=3D S_IFREG; inode->i_size =3D size; mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER); + mapping_set_folio_order_range(inode->i_mapping, 0, 0); mapping_set_inaccessible(inode->i_mapping); /* Unmovable mappings are supposed to be marked unevictable as well. */ WARN_ON_ONCE(!mapping_unevictable(inode->i_mapping)); --=20 2.43.0