On Tue, Oct 25, 2016 at 03:26:48PM +0200, Maxime Ripard wrote: > On Tue, Oct 25, 2016 at 07:38:55AM +0200, LABBE Corentin wrote: > > On Mon, Oct 24, 2016 at 10:10:20PM +0200, Maxime Ripard wrote: > > > On Sat, Oct 22, 2016 at 03:53:28PM +0200, Corentin Labbe wrote: > > > > Since SID's content is constant over reboot, > > > > > > That's not true, at least not across all the Allwinner SoCs, and > > > especially not on the A10 and A20 that this driver supports. > > > > > > > On my cubieboard2 (A20) > > hexdump -C /sys/devices/platform/soc\@01c00000/1c23800.eeprom/sunxi-sid0/nvmem > > 00000000 16 51 66 83 80 48 50 72 56 54 48 48 03 c2 75 72 |.Qf..HPrVTHH..ur| > > 00000010 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| > > * > > 00000100 16 51 66 83 80 48 50 72 56 54 48 48 03 c2 75 72 |.Qf..HPrVTHH..ur| > > 00000110 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| > > * > > 00000200 > > cubiedev ~ # reboot > > cubiedev ~ # hexdump -C /sys/devices/platform/soc\@01c00000/1c23800.eeprom/sunxi-sid0/nvmem > > 00000000 16 51 66 83 80 48 50 72 56 54 48 48 03 c2 75 72 |.Qf..HPrVTHH..ur| > > 00000010 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| > > * > > 00000100 16 51 66 83 80 48 50 72 56 54 48 48 03 c2 75 72 |.Qf..HPrVTHH..ur| > > 00000110 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| > > * > > 00000200 > > > > So clearly for me its constant. > > It's constant across reboots, but not across devices. Each device have > a different SID content, therefore it's a relevant source of entropy > in the system. > Not the 3 leading digit and not the tailing zeros which are the same accross device. So only 50% of data are really different accross devices. Perhaps a "random-range" property could be used ? Herbert, does it is safe to add that 50% duplicate content via add_device_randomness() ? Reading add_device_randomness doc, it seems finally it is safe, but if you could confirm it. Regards -- To unsubscribe from this list: send the line "unsubscribe linux-crypto" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
