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

["Jason A. Donenfeld" <Jason@zx2c4.com>]

On Tue, Jun 18, 2024 at 10:45:48AM +0200, Peter Zijlstra wrote:
> 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:
> 
>   https://discourse.llvm.org/t/rfc-enforcing-bounds-safety-in-c-fbounds-safety/70854

Alright, I'll have this for v+1. Patches already written now, for both
kernel and libc, and I'm dogfooding it.

Jason