diff options
| -rw-r--r-- | arch/x86/mm/kaslr.c | 10 | ||||
| -rw-r--r-- | drivers/pci/Kconfig | 6 | ||||
| -rw-r--r-- | mm/Kconfig | 12 |
3 files changed, 13 insertions, 15 deletions
diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c index 3c306de52fd4..834641c6049a 100644 --- a/arch/x86/mm/kaslr.c +++ b/arch/x86/mm/kaslr.c @@ -115,12 +115,12 @@ void __init kernel_randomize_memory(void) /* * Adapt physical memory region size based on available memory, - * except when CONFIG_PCI_P2PDMA is enabled. P2PDMA exposes the - * device BAR space assuming the direct map space is large enough - * for creating a ZONE_DEVICE mapping in the direct map corresponding - * to the physical BAR address. + * except when CONFIG_ZONE_DEVICE is enabled. ZONE_DEVICE wants to map + * any physical address into the direct-map. KASLR wants to reliably + * steal some physical address bits. Those design choices are in direct + * conflict. */ - if (!IS_ENABLED(CONFIG_PCI_P2PDMA) && (memory_tb < kaslr_regions[0].size_tb)) + if (!IS_ENABLED(CONFIG_ZONE_DEVICE) && (memory_tb < kaslr_regions[0].size_tb)) kaslr_regions[0].size_tb = memory_tb; /* diff --git a/drivers/pci/Kconfig b/drivers/pci/Kconfig index 00b0210e1f1d..e3f848ffb52a 100644 --- a/drivers/pci/Kconfig +++ b/drivers/pci/Kconfig @@ -225,12 +225,6 @@ config PCI_P2PDMA P2P DMA transactions must be between devices behind the same root port. - Enabling this option will reduce the entropy of x86 KASLR memory - regions. For example - on a 46 bit system, the entropy goes down - from 16 bits to 15 bits. The actual reduction in entropy depends - on the physical address bits, on processor features, kernel config - (5 level page table) and physical memory present on the system. - If unsure, say N. config PCI_LABEL diff --git a/mm/Kconfig b/mm/Kconfig index bd0ea5454af8..a992f2203eb9 100644 --- a/mm/Kconfig +++ b/mm/Kconfig @@ -1220,10 +1220,14 @@ config ZONE_DEVICE Device memory hotplug support allows for establishing pmem, or other device driver discovered memory regions, in the memmap. This allows pfn_to_page() lookups of otherwise - "device-physical" addresses which is needed for using a DAX - mapping in an O_DIRECT operation, among other things. - - If FS_DAX is enabled, then say Y. + "device-physical" addresses which is needed for DAX, PCI_P2PDMA, and + DEVICE_PRIVATE features among others. + + Enabling this option will reduce the entropy of x86 KASLR memory + regions. For example - on a 46 bit system, the entropy goes down + from 16 bits to 15 bits. The actual reduction in entropy depends + on the physical address bits, on processor features, kernel config + (5 level page table) and physical memory present on the system. # # Helpers to mirror range of the CPU page tables of a process into device page |