From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793187659; b=RIqlyxSJujfFwNyAq40ARDV0S+CH1W57LDgoRmv6eHlD+4GEs5x+o5wYLWzbrkHDuheq IFerlYxZyEyXsjZw2BSxmwwucYl8DHbJMcVadbxSn8wcwFYKsaUOlzQFObbsJ1HZV79n2 MHbZ2KdweckSaxxKeBFI4r5OH+UOlKkGiKd59Zqxrgy4rgJc3tQ6rwTicmL4Z8ydA2tMY GK6CuilTD6bFgBjnGCFoI4Fb0n+ozbNCfznm3x5XQT+FtsdKzs1FjOuyPdZC6V77X++oM dPFbLby9UZ1whIZ6M1yH1PZGdeockC2H4OObVZPBOTfsHi2YJ0WlWO4YAK+VApqGU5w== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793187659; h=Received:DKIM-Signature:From:To:Cc:Subject:In-Reply-To:References: Date:Message-ID:User-Agent:MIME-Version:Content-Type; bh=Jlnfz7M1ITZw2qIEVKqbY+WjiMkAWf1Tu97ZUZ93IN0=; b=wGvvJ7/j9XGMwhfpGhv0MQtlJN6t3KHirj0fDxG/SpwIMovA2bF7iTF6u5IFMn9iBdi6 u8d5MIvTtaRn48n7mVdNu1eCi3QhwNqdpCkB+aGoHsIA8owzfQZCicwMJALNswPibwhWQ GuI4InQHiINYNjx/rs1Cm9CYfmkbD7d0kSE2KlMWqNQbX9GJ2j2+Ta/O5L7dFpALwLIef cz75UEY9QMqp1isuWb+PB1J6nvAdPIfnNAW7xqZ+oLtVKpPY7RVUSd2ywNJMuUnc7DmBc YKb0beieRgj2bAm+7igA15O94DpYHLWPcsj6f26HfGFQm/YbzJo/GAP8T8n/JgiQxWg== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=PiZ+2Gl5; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6C898606A31C; Wed, 28 Oct 2026 11:40:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=PiZ+2Gl5 Received: by smtp.kernel.org (Postfix) with ESMTPSA id A41CA1F01825; Wed, 28 Oct 2026 11:40:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793187659; bh=Jlnfz7M1ITZw2qIEVKqbY+WjiMkAWf1Tu97ZUZ93IN0=; h=From:To:Cc:Subject:In-Reply-To:References:Date; b=PiZ+2Gl5kc0jJSeKMLoj7fOmlVIOFgswoanYFqn1DWdsQBEuhQPix9JVy9oWukGPG +F4YsgXNS1WGjwV30hoP8na9F/N7Eb7122WwInn552HizyxxW3YaCESCfroMU6yjAm VSLYDm5acEbC8X+0g/aR2w/YcyxdJoeMZDvuNVvBD2N8xDX/JIOe5gr86tQJIXfRoq 39Z0YQ1Uj9IsiFhECBTs0uTCctxqUM5+Y5krqY7Am0KOxTRvkUfV1a6g8jHytioWqL s93d076CkgIdrXOUk2WhEjj/95/4ACkRiIc76P4JQh7Skxr0Cekil6YVf24aF8v9MO VTNrBK9m2sErA== From: Pratyush Yadav To: "David Hildenbrand (Arm)" Cc: Pratyush Yadav , Andrew Morton , Johannes Weiner , Michal Hocko , Qi Zheng , Shakeel Butt , Lorenzo Stoakes , Kairui Song , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Baoquan He , Baolin Wang , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Kees Cook , Peter Zijlstra , Jann Horn , Pedro Falcato , Hugh Dickins , Pasha Tatashin , "Matthew Wilcox (Oracle)" , Jan Kara , Zi Yan , Lance Yang , Rik van Riel , Harry Yoo , Alistair Popple , Nico Pache , Ryan Roberts , Dev Jain , Usama Arif , Kiryl Shutsemau , Matthew Brost , John Hubbard , Peter Xu , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Oscar Salvador , Minchan Kim , Muchun Song , Xu Xin , Chengming Zhou , Chris Li , Kemeng Shi , Nhat Pham , Youngjun Park , Gregory Price , Joshua Hahn , Rakie Kim , Ying Huang , Jason Gunthorpe , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kexec@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-cxl@vger.kernel.org, Chris Mason , stable@vger.kernel.org Subject: Re: [PATCH 20/46] mm/gup: fix clearing folios in memfd_pin_folios() In-Reply-To: (David Hildenbrand's message of "Tue, 27 Oct 2026 20:20:43 +0100") References: <20261027-fixes_core-v1-0-6f74bec9a5bb@kernel.org> <20261027-fixes_core-v1-20-6f74bec9a5bb@kernel.org> <2vxzbj8fp4sn.fsf@kernel.org> Date: Wed, 28 Oct 2026 12:40:48 +0100 Message-ID: <2vxzld7injcv.fsf@kernel.org> User-Agent: Gnus/5.13 (Gnus v5.13) X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain On Tue, Oct 27 2026, David Hildenbrand (Arm) wrote: > On 10/27/26 16:00, Pratyush Yadav wrote: >> On Tue, Oct 27 2026, David Hildenbrand (Arm) wrote: >> >>> From: Chris Mason >>> >>> memfd_pin_folios() pins folios obtained directly from the page cache >>> without checking whether they are uptodate. However, shmem fallocate() >>> can leave newly allocated folios uncleared and not uptodate. Callers >>> such as udmabuf can then expose uninitialized memory to userspace. >>> >>> Clear non-uptodate folios and mark them uptodate under the folio lock >>> before returning them to the caller. >>> >>> Fix generated by an LLM and sent by Chris Mason in private. >>> >>> Fixes: 89c1905d9c14 ("mm/gup: introduce memfd_pin_folios() for pinning memfd folios") >>> Cc: stable@vger.kernel.org >>> Signed-off-by: Chris Mason >>> [ david: simplify description and comment ] >>> Signed-off-by: David Hildenbrand (Arm) >>> --- >>> mm/gup.c | 14 ++++++++++++++ >>> 1 file changed, 14 insertions(+) >>> >>> diff --git a/mm/gup.c b/mm/gup.c >>> index efc9aa2654625..47e7ae152cdf1 100644 >>> --- a/mm/gup.c >>> +++ b/mm/gup.c >>> @@ -3516,6 +3516,20 @@ long memfd_pin_folios(struct file *memfd, loff_t start, loff_t end, >>> goto err; >>> } >>> >>> + /* >>> + * fallocate() can leave folios in the >>> + * page cache that were never cleared. >>> + */ >>> + if (!folio_test_uptodate(folio)) { >>> + folio_lock(folio); >>> + if (!folio_test_uptodate(folio)) { >>> + folio_zero_range(folio, 0, folio_size(folio)); >>> + flush_dcache_folio(folio); >>> + folio_mark_uptodate(folio); >>> + } >>> + folio_unlock(folio); >>> + } >>> + >> >> Nit: this logic is repeated in a couple places in shmem.c and in >> memfd_luo.c. Perhaps it deserves a helper? >> >> Anyway, sounds like an important fix so don't make my nitpick stop you >> from landing this if you don't want to bother. > > Thanks! yeah, I had the same thought when trying to improve this. We should have > an easier way to just not hand out unzeroed folios outside of shmem core > functions in the first place ... Normally this should use shmem_read_folio() to get all the folios, which does zero the folios before handing them out. I guess memfd_pin_folios() uses filemap_get_folios_contig() for performance reasons. It does the lookup under RCU and doesn't need to take the folio lock. Perhaps we need a shmem_get_folios_contig()? -- Regards, Pratyush Yadav