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SubjectRe: [PATCH v2 1/3] bpf: Add bpf_verify_pkcs7_signature() helper
On Wed, Jun 8, 2022 at 4:43 PM Daniel Borkmann <daniel@iogearbox.net> wrote:
>
> 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.

Can we keep the helper generic so that it can be extended to more types of
signatures and pass the signature type as an enum?

bpf_verify_signature and a type SIG_PKCS7 or something.

> >
> > 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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