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h=Date:From:To:Cc:Subject:In-Reply-To:References; b=kI0Tv3mJEIZm9VmEyQS5AwmIRYNpAFOrDXTC1qjfpugX0SgopyQV1yg1j+BDA0vlt I/P3PBDHU+ENnuMqS/E4joZ6HmZsW9U7+RvsE9/saNTWOUqIYYJ+QLN1NV3TbB/VJv n/a6ziIjuJXld2ySdpOXUXAlXVjPSRQ0LZeFoZmM= Date: Sat, 5 Sep 2026 16:03:12 -0700 From: Andrew Morton To: Ren Wei Cc: linux-mm@kvack.org, david@kernel.org, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, notasas@gmail.com, vega@nebusec.ai, rakukuip@gmail.com Subject: Re: [PATCH v2 1/1] mm/memory: constrain generic_access_phys() to page boundary Message-Id: <20260905160312.9717eb43a63bed4de9f0248b@linux-foundation.org> In-Reply-To: References: X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Stat-Signature: yr68u5j7e4t33xyjpdne491nrudzqgfd X-Rspamd-Queue-Id: 6D55A100002 X-Rspamd-Server: rspam06 X-HE-Tag: 1788649394-655301 X-HE-Meta: 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 nLknrVyU eGCgg5dhvUdeb7ha8r7VT5N35eUoQhi98Jidr/iNQsBYZeszNDcorMSgQbddzPWROizaG4rxWdW8KvEOvoG5JJfIyQKh10knOFLEQhMmWmnSSNftv2Np/3DCEE3piv2C77VLM0s+Zm0Bwa1De79YrAelUNoqN0kVZlZpDlktgFUdDjvFIWe0NhSOvL588BSHQhLdQIcj1a36bYcQpn08Ozy8H7u7GB3TVMWR7VQtXbhMjbyqd9HDETURZqW6Mw7OzPa2kITbpP7AL/8+B+ihdjZBBaAtY9UhZrB1Ae+T6YUiCxT9gyJf69BTO2Ril6NSEdHiO Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sat, 5 Sep 2026 22:12:17 +0800 Ren Wei wrote: > generic_access_phys() improperly validates the memory access range: it > only validates the start address using follow_pfnmap_start() and passes > PAGE_ALIGN(len + offset) to ioremap_prot(). > > This poses two problems: > 1. In PFNMAP VMAs, consecutive virtual pages are not guaranteed to be > physically contiguous, and individual PTEs may have different access > permissions or writability. > 2. The mapping may cross VMA boundaries if len extends beyond vma->vm_end. > > Since __access_remote_vm() already loops over the requested length and > accesses normal (struct page) memory page-by-page, constrain the ->access() > callback in __access_remote_vm() to at most the current page boundary. > Because VMA boundaries are always page-aligned, this also ensures the > access never exceeds the current VMA. > > In generic_access_phys(), defensively clamp len to the page boundary as > well, map only a single PAGE_SIZE via ioremap_prot(), and add a missing > (resource_size_t) cast during PFN re-validation to avoid truncation on > 32-bit PAE systems. Thanks. > Fixes: 9cb12d7b4cca ("mm/memory.c: actually remap enough memory") > Cc: stable@vger.kernel.org Why are we proposing a backport? To do that we should provide recipients with a clear description of the userspace-visible runtime affects of this bug and I'm not seeing that in the changelog?