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owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 11/8/25 13:32, Dan Williams wrote: > Commit 7ffb791423c7 ("x86/kaslr: Reduce KASLR entropy on most x86 systems") > is too narrow. ZONE_DEVICE, in general, lets any physical address be added > to the direct-map. I.e. not only ACPI hotplug ranges, CXL Memory Windows, > or EFI Specific Purpose Memory, but also any PCI MMIO range for the > CONFIG_DEVICE_PRIVATE and CONFIG_PCI_P2PDMA cases. > > A potential path to recover entropy would be to walk ACPI and determine the > limits for hotplug and PCI MMIO before kernel_randomize_memory(). On > smaller systems that could yield some KASLR address bits. This needs > additional investigation to determine if some limited ACPI table scanning > can happen this early without an open coded solution like > arch/x86/boot/compressed/acpi.c needs to deploy. > > Cc: Balbir Singh > Cc: Ingo Molnar > Cc: Kees Cook > Cc: Bjorn Helgaas > Cc: Peter Zijlstra > Cc: Andy Lutomirski > Cc: Logan Gunthorpe > Cc: Andrew Morton > Cc: David Hildenbrand > Cc: Lorenzo Stoakes > Cc: "Liam R. Howlett" > Cc: Vlastimil Babka > Cc: Mike Rapoport > Cc: Suren Baghdasaryan > Cc: Michal Hocko > Cc: "Yasunori Gotou (Fujitsu)" > Fixes: 7ffb791423c7 ("x86/kaslr: Reduce KASLR entropy on most x86 systems") > Signed-off-by: Dan Williams P2PDMA requires ZONE_DEVICE, Most distros have P2PDMA enabled, you mention smaller devices - are you referring to kernels/distros where P2PDMA is not enabled and only ZONE_DEVICE is? Balbir