Re: [PATCH 0/5] lib/crypto: Handle large lengths in poly1305 and chacha20poly1305

[Eric Biggers <ebiggers@kernel.org>]

On Mon, Oct 12, 2026 at 09:31:17PM +0000, Vladimir Kukharenko via B4 Relay wrote:
> This series makes the Poly1305 and ChaCha20-Poly1305 library code handle
> large lengths:
> 
> - poly1305_update() can write past its 16-byte buffer if it holds a
>   partial block and nbytes >= 2^32 - desc->buflen.
> - The chacha20poly1305 functions use only the low 32 bits of their
>   size_t message and associated data lengths.
> - On 64-bit MIPS and RISC-V, the poly1305 assembly reads past its input
>   for lengths of 2 GiB or more: these ABIs sign-extend its u32 length
>   argument, and the assembly uses all 64 bits.  arm64 has the same
>   prototype mismatch, with no known failure.
> 
> Patches 1-3 fix the assembly prototypes, one architecture per patch.
> The assembly already treats the length as 64-bit, so they declare it as
> size_t, as commit f3d6cb3dc039 ("lib/crypto: x86/sha1: Migrate
> optimized code into library") did for the x86 SHA-1 assembly.
> Patches 4 and 5 make poly1305_update() and chacha_crypt() take size_t
> lengths.  The patches apply independently, except that on 64-bit MIPS
> and RISC-V patch 4 relies on patches 1 and 2 for inputs of 2 GiB or more.
> 
> No in-tree caller passes inputs this large (WireGuard passes at most one
> packet, big_key at most 1 MiB), so I consider these ABI robustness
> improvements rather than fixes and have not added Fixes or Cc stable tags.
> 
> I tested with the lib/crypto KUnit suite on UML, x86_64, i386, arm64,
> riscv64 and mips64, with a temporary 2 GiB KUnit test on arm64, riscv64
> and mips64 (it oopses on riscv64 and mips64 without patches 1 and 2), and
> in userspace against OpenSSL for inputs above 4 GiB.
> 
> I found the bugs fixed by patches 4 and 5 while writing Coq/VST proofs of
> this code with LLM agents, and an LLM review of patch 4 found the one
> fixed by patches 1-3.  I used an LLM-based assistant to write the patches
> and descriptions, and reviewed its work.

Thanks!  Patches 1-3 look good.  I'm less sure about patches 4-5, since
they go through some trouble to work around (some implementations of)
poly1305_blocks() and chacha_crypt_arch() not taking size_t.  Wouldn't
it make sense to convert those to size_t at the same time?

- Eric