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:

quoted

On Fri, Jun 14, 2024 at 12:08 PM Jason A. Donenfeld [off-list ref] wrote:

quoted

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