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SubjectRe: [PATCH v2 1/3] bpf: Add bpf_verify_pkcs7_signature() helper
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On 6/8/22 1:12 PM, Roberto Sassu wrote:
> Add the bpf_verify_pkcs7_signature() helper, to give the ability to eBPF
> security modules to check the validity of a PKCS#7 signature against
> supplied data.
>
> Use the 'keyring' parameter to select the keyring containing the
> verification key: 0 for the primary keyring, 1 for the primary and
> secondary keyrings, 2 for the platform keyring.
>
> Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
> ---
> include/uapi/linux/bpf.h | 8 ++++++++
> kernel/bpf/bpf_lsm.c | 32 ++++++++++++++++++++++++++++++++
> tools/include/uapi/linux/bpf.h | 8 ++++++++
> 3 files changed, 48 insertions(+)
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index f4009dbdf62d..40d0fc0d9493 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -5249,6 +5249,13 @@ union bpf_attr {
> * Pointer to the underlying dynptr data, NULL if the dynptr is
> * read-only, if the dynptr is invalid, or if the offset and length
> * is out of bounds.
> + *
> + * long bpf_verify_pkcs7_signature(u8 *data, u32 datalen, u8 *sig, u32 siglen, u64 keyring)
> + * Description
> + * Verify the PKCS#7 *sig* with length *siglen*, on *data* with
> + * length *datalen*, with key in *keyring*.

Could you also add a description for users about the keyring argument and guidance on when
they should use which in their programs? Above is a bit too terse, imho.

> + * Return
> + * 0 on success, a negative value on error.
> */
> #define __BPF_FUNC_MAPPER(FN) \
> FN(unspec), \
> @@ -5455,6 +5462,7 @@ union bpf_attr {
> FN(dynptr_read), \
> FN(dynptr_write), \
> FN(dynptr_data), \
> + FN(verify_pkcs7_signature), \
> /* */
>
> /* integer value in 'imm' field of BPF_CALL instruction selects which helper
> diff --git a/kernel/bpf/bpf_lsm.c b/kernel/bpf/bpf_lsm.c
> index c1351df9f7ee..1cda43cb541a 100644
> --- a/kernel/bpf/bpf_lsm.c
> +++ b/kernel/bpf/bpf_lsm.c
> @@ -16,6 +16,7 @@
> #include <linux/bpf_local_storage.h>
> #include <linux/btf_ids.h>
> #include <linux/ima.h>
> +#include <linux/verification.h>
>
> /* For every LSM hook that allows attachment of BPF programs, declare a nop
> * function where a BPF program can be attached.
> @@ -132,6 +133,35 @@ static const struct bpf_func_proto bpf_get_attach_cookie_proto = {
> .arg1_type = ARG_PTR_TO_CTX,
> };
>
> +BPF_CALL_5(bpf_verify_pkcs7_signature, u8 *, data, u32, datalen, u8 *, sig,
> + u32, siglen, u64, keyring)
> +{
> + int ret = -EOPNOTSUPP;
> +
> +#ifdef CONFIG_SYSTEM_DATA_VERIFICATION
> + if (keyring > (unsigned long)VERIFY_USE_PLATFORM_KEYRING)
> + return -EINVAL;
> +
> + ret = verify_pkcs7_signature(data, datalen, sig, siglen,
> + (struct key *)keyring,
> + VERIFYING_UNSPECIFIED_SIGNATURE, NULL,
> + NULL);
> +#endif
> + return ret;
> +}

Looks great! One small nit, I would move all of the BPF_CALL and _proto under the
#ifdef CONFIG_SYSTEM_DATA_VERIFICATION ...

> +static const struct bpf_func_proto bpf_verify_pkcs7_signature_proto = {
> + .func = bpf_verify_pkcs7_signature,
> + .gpl_only = false,
> + .ret_type = RET_INTEGER,
> + .arg1_type = ARG_PTR_TO_MEM,
> + .arg2_type = ARG_CONST_SIZE_OR_ZERO,
> + .arg3_type = ARG_PTR_TO_MEM,
> + .arg4_type = ARG_CONST_SIZE_OR_ZERO,
> + .arg5_type = ARG_ANYTHING,
> + .allowed = bpf_ima_inode_hash_allowed,
> +};
> +
> static const struct bpf_func_proto *
> bpf_lsm_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
> {
> @@ -158,6 +188,8 @@ bpf_lsm_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
> return prog->aux->sleepable ? &bpf_ima_file_hash_proto : NULL;
> case BPF_FUNC_get_attach_cookie:
> return bpf_prog_has_trampoline(prog) ? &bpf_get_attach_cookie_proto : NULL;
> + case BPF_FUNC_verify_pkcs7_signature:
> + return prog->aux->sleepable ? &bpf_verify_pkcs7_signature_proto : NULL;

... same here:

#ifdef CONFIG_SYSTEM_DATA_VERIFICATION
case BPF_FUNC_verify_pkcs7_signature:
return prog->aux->sleepable ? &bpf_verify_pkcs7_signature_proto : NULL;
#endif

So that bpftool or other feature probes can check for its availability. Otherwise, apps have
a hard time checking whether bpf_verify_pkcs7_signature() helper is available for use or not.

> default:
> return tracing_prog_func_proto(func_id, prog);
> }
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index f4009dbdf62d..40d0fc0d9493 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -5249,6 +5249,13 @@ union bpf_attr {
> * Pointer to the underlying dynptr data, NULL if the dynptr is
> * read-only, if the dynptr is invalid, or if the offset and length
> * is out of bounds.
> + *
> + * long bpf_verify_pkcs7_signature(u8 *data, u32 datalen, u8 *sig, u32 siglen, u64 keyring)
> + * Description
> + * Verify the PKCS#7 *sig* with length *siglen*, on *data* with
> + * length *datalen*, with key in *keyring*.
> + * Return
> + * 0 on success, a negative value on error.
> */
> #define __BPF_FUNC_MAPPER(FN) \
> FN(unspec), \
> @@ -5455,6 +5462,7 @@ union bpf_attr {
> FN(dynptr_read), \
> FN(dynptr_write), \
> FN(dynptr_data), \
> + FN(verify_pkcs7_signature), \
> /* */
>
> /* integer value in 'imm' field of BPF_CALL instruction selects which helper
>

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