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SubjectRE: [PATCH v2 1/3] bpf: Add bpf_verify_pkcs7_signature() helper
Date
> From: Daniel Borkmann [mailto:daniel@iogearbox.net]
> Sent: Wednesday, June 8, 2022 4:43 PM
> 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.

Hi Daniel

sure, will do.

> > + * 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 ...

Ok.

> > +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.

Ok.

I'm currently fixing the test. The challenge is that the module_signature
structure might not be defined. The way I found to fix it is to include
stdlib.h and linux/bpf.h instead of vmlinux.h, and always define the
structure.

Will also skip the test if CONFIG_MODULE_SIG is not defined.

About the CI, I noticed that the kernel configuration file is in the travis
directory. I modified tools/selftests/bpf/config to update the dependencies
for the new helper.

Maybe we should merge both configs at the time the kernel is built?

Thanks

Roberto

HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063
Managing Director: Li Peng, Yang Xi, Li He

> > 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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