Messages in this thread | | | From | Kees Cook <> | Date | Mon, 30 Apr 2018 12:16:45 -0700 | Subject | Re: Hashed pointer issues |
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On Mon, Apr 30, 2018 at 12:00 PM, Linus Torvalds <torvalds@linux-foundation.org> wrote: > On Mon, Apr 30, 2018 at 11:38 AM Kees Cook <keescook@chromium.org> wrote: > >> Something like this? (Untested.) > > Looks workable. > >> + /* If we have hw RNG, start hashing immediately. */ >> + if (arch_has_random()) { >> + get_random_bytes_arch(&ptr_key, sizeof(ptr_key)); >> + ptr_key_ready(); >> + return 0; >> + } > > Small tweak: you should check the return value of get_random_bytes_arch(), > because in theory it can fail. > > Sadly, that's not actually how get_random_bytes_arch() really works - it > falls back on "get_random_bytes()" on failure instead, which is explicitly > against the whole point here.
I just noticed: there are _no_ users of get_random_bytes_arch() ... didn't we once use it to feed entropy to the CRNG?
> So I think it would need some tweaking, with a new function entirely > (get_random_bytes_arch() with a failure return for "cannot fill buffer"). > > But that would be just a few more lines, because we could make the existing > get_random_bytes_arch() just use the failure-case thing. > > So add a "get_hw_random_bytes()" that does that same loop in > get_random_bytes_arch(), but returns the number of bytes it filled in. > > Then get_random_bytes_arch() turns into > > got = get_hw_random_bytes(p, nbytes); > if (got < nbytes) > get_random_bytes(p+got, nbytes-got); > > and the initialize_ptr_random() use would be something like > > if (get_hw_random_bytes(&ptr_key, sizeof(ptr_key)) == sizeof(ptr_key)) { > ptr_key_ready(); > return 0; > } > > Hmm? > > Maybe we could call the "get_hw_random_bytes()" something like > "get_early_random_bytes()" and the "use HW for it" is purely an > implementation detail?
Yeah, and if we add __must_check, I think this should be fine. Ted, any thoughts on this?
Tobin, is this something you've got time to implement and test?
-Kees
-- Kees Cook Pixel Security
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