Messages in this thread | | | Date | Tue, 1 May 2018 07:23:05 +1000 | From | "Tobin C. Harding" <> | Subject | Re: Hashed pointer issues |
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On Mon, Apr 30, 2018 at 12:16:45PM -0700, Kees Cook wrote: > 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?
Sure thing, thanks for the opportunity.
Tobin
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