Re: [PATCH v2 1/3] bpf: Add bpf_verify_pkcs7_signature() helper

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