Re: [PATCH bpf-next v2 2/5] bpf: Add SHA hash kfunc for cryptographic hashing

Daniel Hodges
2025-12-08T01:29:02Z

On Fri, Dec 05, 2025 at 06:50:48PM +0000, Mykyta Yatsenko wrote:
> On 12/5/25 17:39, Daniel Hodges wrote:
> > Extend bpf_crypto_type structure with hash operations:
> > - hash(): Performs hashing operation
> > - digestsize(): Returns hash output size
> >
> > Update bpf_crypto_ctx_create() to support keyless operations:
> > - Hash algorithms don't require keys, unlike ciphers
> > - Only validates key presence if type->setkey is defined
> > - Conditionally sets IV/state length for cipher operations only
> >
> > Add bpf_crypto_hash() kfunc that works with any hash algorithm
> > registered in the kernel's crypto API through the BPF crypto type
> > system. This enables BPF programs to compute cryptographic hashes for
> > use cases such as content verification, integrity checking, and data
> > authentication.
> >
> > Signed-off-by: Daniel Hodges <git@danielhodges.dev>
> > ---
> > include/linux/bpf_crypto.h | 2 +
> > kernel/bpf/crypto.c | 76 ++++++++++++++++++++++++++++++++++----
> > 2 files changed, 70 insertions(+), 8 deletions(-)
> >
> > diff --git a/include/linux/bpf_crypto.h b/include/linux/bpf_crypto.h
> > index a41e71d4e2d9..c84371cc4e47 100644
> > --- a/include/linux/bpf_crypto.h
> > +++ b/include/linux/bpf_crypto.h
> > @@ -11,8 +11,10 @@ struct bpf_crypto_type {
> > int (*setauthsize)(void *tfm, unsigned int authsize);
> > int (*encrypt)(void *tfm, const u8 *src, u8 *dst, unsigned int len, u8 *iv);
> > int (*decrypt)(void *tfm, const u8 *src, u8 *dst, unsigned int len, u8 *iv);
> > + int (*hash)(void *tfm, const u8 *data, u8 *out, unsigned int len);
> > unsigned int (*ivsize)(void *tfm);
> > unsigned int (*statesize)(void *tfm);
> > + unsigned int (*digestsize)(void *tfm);
> > u32 (*get_flags)(void *tfm);
> > struct module *owner;
> > char name[14];
> > diff --git a/kernel/bpf/crypto.c b/kernel/bpf/crypto.c
> > index 83c4d9943084..95625c7ffb1a 100644
> > --- a/kernel/bpf/crypto.c
> > +++ b/kernel/bpf/crypto.c
> > @@ -171,7 +171,12 @@ bpf_crypto_ctx_create(const struct bpf_crypto_params *params, u32 params__sz,
> > goto err_module_put;
> > }
> > - if (!params->key_len || params->key_len > sizeof(params->key)) {
> > + /* Hash operations don't require a key, but cipher operations do */
> > + if (params->key_len > sizeof(params->key)) {
> > + *err = -EINVAL;
> > + goto err_module_put;
> > + }
> > + if (!params->key_len && type->setkey) {
> > *err = -EINVAL;
> > goto err_module_put;
> > }
> > @@ -195,16 +200,19 @@ bpf_crypto_ctx_create(const struct bpf_crypto_params *params, u32 params__sz,
> > goto err_free_tfm;
> > }
> > - *err = type->setkey(ctx->tfm, params->key, params->key_len);
> > - if (*err)
> > - goto err_free_tfm;
> > + if (params->key_len) {
> > + *err = type->setkey(ctx->tfm, params->key, params->key_len);
> > + if (*err)
> > + goto err_free_tfm;
> > - if (type->get_flags(ctx->tfm) & CRYPTO_TFM_NEED_KEY) {
> > - *err = -EINVAL;
> > - goto err_free_tfm;
> > + if (type->get_flags(ctx->tfm) & CRYPTO_TFM_NEED_KEY) {
> > + *err = -EINVAL;
> > + goto err_free_tfm;
> > + }
> > }
> > - ctx->siv_len = type->ivsize(ctx->tfm) + type->statesize(ctx->tfm);
> > + if (type->ivsize && type->statesize)
> > + ctx->siv_len = type->ivsize(ctx->tfm) + type->statesize(ctx->tfm);
> > refcount_set(&ctx->usage, 1);
> > @@ -343,6 +351,54 @@ __bpf_kfunc int bpf_crypto_encrypt(struct bpf_crypto_ctx *ctx,
> > return bpf_crypto_crypt(ctx, src_kern, dst_kern, siv_kern, false);
> > }
> > +#if IS_ENABLED(CONFIG_CRYPTO_HASH2)
> > +/**
> > + * bpf_crypto_hash() - Compute hash using configured context
> > + * @ctx: The crypto context being used. The ctx must be a trusted pointer.
> > + * @data: bpf_dynptr to the input data to hash. Must be a trusted pointer.
> > + * @out: bpf_dynptr to the output buffer. Must be a trusted pointer.
> > + *
> > + * Computes hash of the input data using the crypto context. The output buffer
> > + * must be at least as large as the digest size of the hash algorithm.
> > + */
> > +__bpf_kfunc int bpf_crypto_hash(struct bpf_crypto_ctx *ctx,
> > + const struct bpf_dynptr *data,
> > + const struct bpf_dynptr *out)
> > +{
> > + const struct bpf_dynptr_kern *data_kern = (struct bpf_dynptr_kern *)data;
> > + const struct bpf_dynptr_kern *out_kern = (struct bpf_dynptr_kern *)out;
> > + u32 data_len, out_len;
> > + const u8 *data_ptr;
> > + u8 *out_ptr;
> > +
> > + if (!ctx->type->hash)
> > + return -EOPNOTSUPP;
> > +
> > + data_len = __bpf_dynptr_size(data_kern);
> > + out_len = __bpf_dynptr_size(out_kern);
> __bpf_dynptr_size() returns u64, as well as __bpf_dynptr_data_rw()
> takes u64 as length parameter, it may be worth using that type for
> data_len and out_len.

Yeah, that makes sense, will queue that up.