On Mon, Apr 14, 2014 at 8:49 AM, Andy Lutomirski <[email protected]> wrote: > [Resent because I forgot to email lkml. This also surreptitiously > fixes a silly typo on a patch description.] > > This is my attempt to come up with a workable way to use so-called > entropy sources like a TPM to feed /dev/urandom. > > Arguably we should be feeding the input pool as well, but if the > /dev/random algorithm is correct, this shouldn't matter. I don't want > sensible use of TPMs for /dev/urandom to block on a long debate about > /dev/random, so these patches have no effect on /dev/random.
Please consider these patches withdrawn. I'll redo them on top of the hwrng stuff. Reasons: - add_drbg_randomness can probably be replaced with add_device_randomness. I'm not convinced that I like add_device_randomness as a way to add small amounts of entropy: if an attacker knows the initial state of the nonblocking pool, they can use it to back out small amounts of entropy added via add_device_randomness, which allows them to track all input_pool entropy added by add_device_randomness. This type of attack is impractical for large amounts of device randomness added at once, so this is orthogonal to the purpose of my patches. - The hwrng code itself is already a sensible place to do this kind of initial seeding of the nonblocking pool, so I think that it would be better to improve the hwrng code a bit instead. My current thought is to split CONFIG_HW_RANDOM into CONFIG_HW_RANDOM_DEVICES and CONFIG_HW_RANDOM. CONFIG_HW_RANDOM_DEVICES will default to m and will expose hwrng_register but not the /dev/hwrng code. hwrng_register will call add_device_randomness, but I'll add logging so that we can tell that it's working. I'll also rewrite the tpm hwrng driver. There should be a hwrng instance per TPM, and it shouldn't show up until there's actually a TPM there. --Andy > > Andy Lutomirski (2): > random: Add add_drbg_randomness to safely seed urandom from crypto hw > tpm,random: Call add_drbg_randomness after selftest > > drivers/char/random.c | 56 > +++++++++++++++++++++++++++++++++++----- > drivers/char/tpm/tpm-interface.c | 15 ++++++++++- > include/linux/random.h | 1 + > include/trace/events/random.h | 19 ++++++++++++++ > 4 files changed, 83 insertions(+), 8 deletions(-) > > -- > 1.9.0 > -- Andy Lutomirski AMA Capital Management, LLC -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
