From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=91.218.175.150 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794132561; b=WEo/T0rpWEahpja/Kix4vPbRnYhkW8iixSDAFeTaoKzVlMuNFIJhZyBCQbnVPg7Nvl7O 0K0OrMB6JZkyXtUUj0QmyxlcxZSJm2cYl/SMYNqn/HF7dyb8CiIO2HIpZUKubZFVgPc0w FL0hihfIO7gllhq6xkyKZyWhWLOey8a0THmw6J0Cf/NcWbxzQ7k3jKFjHMxZ9AwUyovCY hdCy+rkmb+Ilm9A/C5ehzIkbQNaSUfNhDB6xscP6IEpNJETZXfurAPHaaVGjPEwcPMJLv Vgmte1UbqR95WZUIbP+QHG7sy2PYaPHT/J+1l5E+RdwlvmUoGO8yKubt9zfY9WcpCgQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794132561; h=DMARC-Filter:X-Envelope-To:DKIM-Signature:X-Envelope-To:Received: X-Mizu-Trace-ID:X-Migadu-Flow:From:To:Cc:Subject:Date:Message-ID: X-Mailer:In-Reply-To:References:MIME-Version:Content-Type: Content-Transfer-Encoding; bh=bMJlZTOTEJlmOuVWJz4GRAC6Q9ZXPrxhv+08R2sTA74=; b=N69JjqsXbJcdQYzWGh7C2PMrYN6fIV7c1gsLijplJqObW3Ga9nSuFHGJrKFJm3au3Q7U T77s+t1XFgsVdPdm0amy33abBcTcJ8SEGPKXV1wFVxKITRuwcN5tCYhi2s8pi3UOge8xm W5kceK/YQAzTdZtZNrr7MU8tNoIlQBpmUGzXaZpv2YgOV133NJSghTTvruqp8EcLtRtz/ kck33oxtB8vNQ7O9KC3CY7zstbeF2A3YF7QbKxxMI+pQqsKNyVkyfEsD3XGMHvmfQ8oW9 K0O7oGl7Gzvu2/YqEGmdhxa6KUdSAwLZfYfw1eotaecbOJDaVgXKybV2aNPbuEfzRHA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; arc=none smtp.remote-ip=91.218.175.150 Received: from mta0.migadu.com (out-150.mta0.migadu.com [91.218.175.150]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0A48C606A31C for ; Sun, 8 Nov 2026 10:09:08 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 0A48C606A31C Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev X-Envelope-To: stable@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=bMJlZTOTEJlmOuVWJz4GRAC6Q9ZXPrxhv+08R2sTA74=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1794132547; v=1; x=1794737347; b=oJi7KdRqKwDGAFpr7Bmv9zJzxhR4ofd/6SKv8EmW8rADUsNX2np1y5SzvNmn5z4ppLwGdrb/ KxVerOoFanoXU9/Vb9kHUjRBhpKKjfHm1sR0yFld2vc2O5vaimBScxbcCJH+/nS9tTBJnuoOJRb fiaWVOj6l7ZrFkwFxkVXDI68= X-Envelope-To: stable@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 2d28383a0356ad5a; Sun, 08 Nov 2026 10:09:07 +0000 X-Mizu-Trace-ID: 2d28383a0356ad5a X-Migadu-Flow: FLOW_OUT From: Lance Yang To: david@kernel.org Cc: hughd@google.com, baolin.wang@linux.alibaba.com, akpm@linux-foundation.org, david@readahead.eu, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, corbet@lwn.net, skhan@linuxfoundation.org, rdunlap@infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, stable@vger.kernel.org, mason@kernel.org Subject: Re: [PATCH 1/2] mm/memfd: handle GUP pins more reliably when write-sealing Date: Sun, 8 Nov 2026 18:08:57 +0800 Message-ID: <20261108100857.94336-1-lance.yang@linux.dev> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20261103-fixes_core_2-v1-1-f332954f1df4@kernel.org> References: <20261103-fixes_core_2-v1-1-f332954f1df4@kernel.org> X-Mailing-List: stable@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; charset=UTF-8 Content-Transfer-Encoding: 8bit On Tue, Nov 03, 2026 at 07:31:44PM +0100, David Hildenbrand (Arm) wrote: >memfd_wait_for_pins() detects GUP references by comparing a folio's >actual refcount with its expected refcount. As spelled out by >folio_expected_ref_count(), obtaining the expected refcount when there >can be concurrent folio (un)mapping is racy. > >So it is possible that a changing folio mapcount can race with our >check for GUP references, and F_SEAL_WRITE might succeed even if there >are some, allowing file contents to be modified after sealing. > >For folios with a reliable pincount, detect FOLL_PIN references using >folio_maybe_dma_pinned() before falling back to the refcount comparison. >For small folios without that, the 1024 pinning BIAS makes it very hard >(although not impossible) to misguide the refcount comparison. > >This improves FOLL_PIN detection for folios with a pincount. Handling >FOLL_GET and small folios requires a more fundamental change. > >Fortunately, most interfaces that allow for GUP'ing such pages use >FOLL_PIN, in particular interfaces using FOLL_LONGTERM. However, we >still have some FOLL_GET leftovers ... > >Fixes: 05f65b5c7090 ("shm: wait for pins to be released when sealing") >Cc: stable@vger.kernel.org >Cc: Chris Mason >Signed-off-by: David Hildenbrand (Arm) >--- Reviewed-by: Lance Yang