On 4/15/19 11:40 AM, Conrad Meyer wrote: > Author: cem > Date: Mon Apr 15 18:40:36 2019 > New Revision: 346250 > URL: https://svnweb.freebsd.org/changeset/base/346250 > > Log: > random(4): Block read_random(9) on initial seeding > > read_random() is/was used, mostly without error checking, in a lot of > very sensitive places in the kernel -- including seeding the widely used > arc4random(9). > > Most uses, especially arc4random(9), should block until the device is seeded > rather than proceeding with a bogus or empty seed. I did not spy any > obvious kernel consumers where blocking would be inappropriate (in the > sense that lack of entropy would be ok -- I did not investigate locking > angle thoroughly). In many instances, arc4random_buf(9) or that family > of APIs would be more appropriate anyway; that work was done in r345865.
There are definitely places arc4random is used where sleeping is not allowed. ipsec generating nonces for AES-CBC is one example I can think of off the top of my head. I think it might be useful to add an explicit WITNESS_WARN in arc4random to catch these cases so they can be found and reasoned about. > This change primarily impacts the behavior of /dev/random on embedded > systems with read-only media that do not configure "nodevice random". We > toggle the default from 'charge on blindly with no entropy' to 'block > indefinitely.' This default is safer, but may cause frustration. Embedded > system designers using FreeBSD have several options. The most obvious is to > plan to have a small writable NVRAM or NAND to persist entropy, like larger > systems. Early entropy can be fed from any loader, or by writing directly > to /dev/random during boot. Some embedded SoCs now provide a fast hardware > entropy source; this would also work for quickly seeding Fortuna. A 3rd > option would be creating an embedded-specific, more simplistic random > module, like that designed by DJB in [1] (this design still requires a small > rewritable media for forward secrecy). Finally, the least preferred option > might be "nodevice random", although I plan to remove this in a subsequent > revision. Note that I actually often run into unseeded systems when doing development using qemu for non-x86 architectures. For example, when booting mips from qemu, there is no loader, the kernel just starts, and since the endian is opposite, I frequently regenerate the filesystem using makefs. -- John Baldwin _______________________________________________ svn-src-head@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"