On 2025/10/31 18:19, David Hildenbrand wrote:
On 31.10.25 10:59, Mike Rapoport wrote:
On Fri, Oct 31, 2025 at 05:18:18PM +0800, Lance Yang wrote:
From: Lance Yang lance.yang@linux.dev
The error path in secretmem_fault() frees a folio before restoring its direct map status, which is a race leading to a panic.
Let's use the issue description from the report:
When a page fault occurs in a secret memory file created with `memfd_secret(2)`, the kernel will allocate a new folio for it, mark the underlying page as not-present in the direct map, and add it to the file mapping.
If two tasks cause a fault in the same page concurrently, both could end up allocating a folio and removing the page from the direct map, but only one would succeed in adding the folio to the file mapping. The task that failed undoes the effects of its attempt by (a) freeing the folio again and (b) putting the page back into the direct map. However, by doing these two operations in this order, the page becomes available to the allocator again before it is placed back in the direct mapping.
If another task attempts to allocate the page between (a) and (b), and the kernel tries to access it via the direct map, it would result in a supervisor not-present page fault.
Fix the ordering to restore the map before the folio is freed.
... restore the direct map
With these changes
Reviewed-by: Mike Rapoport (Microsoft) rppt@kernel.org
Fully agreed
Acked-by: David Hildenbrand david@redhat.com
Cheers!