Re: [PATCH v17 4/5] random: introduce generic vDSO getrandom() implementation

Peter Zijlstra
2024-06-18T08:46:16Z

On Tue, Jun 18, 2024 at 02:12:40AM +0200, Jason A. Donenfeld wrote:
> Hi Andy,
>
> On Mon, Jun 17, 2024 at 05:06:22PM -0700, Andy Lutomirski wrote:
> > On Fri, Jun 14, 2024 at 12:08 PM Jason A. Donenfeld <Jason@zx2c4.com> wrote:
> > >
> > > Provide a generic C vDSO getrandom() implementation, which operates on
> > > an opaque state returned by vgetrandom_alloc() and produces random bytes
> > > the same way as getrandom(). This has a the API signature:
> > >
> > > ssize_t vgetrandom(void *buffer, size_t len, unsigned int flags, void *opaque_state);
> >
> > Last time around, I mentioned some potential issues with this function
> > signature, and I didn't see any answer. My specific objection was to
> > the fact that the caller passes in a pointer but not a length, and
> > this potentially makes reasoning about memory safety awkward,
> > especially if anything like CRIU is involved.
>
> Oh, I understood this backwards last time - I thought you were
> criticizing the size_t len argument, which didn't make any sense.
>
> Re-reading now, what you're suggesting is that I add an additional
> argument called `size_t opaque_len`, and then the implementation does
> something like:

Exactly, that's how I read amluto's suggestion as well. Also, I recently
ran into this clang rfc: