[PATCH v3 3/9] bpf-lsm: Introduce new helper bpf_ima_file_hash()

Roberto Sassu
2022-03-02T11:15:34Z

ima_file_hash() has been modified to calculate the measurement of a file on
demand, if it has not been already performed by IMA or the measurement is
not fresh. For compatibility reasons, ima_inode_hash() remains unchanged.

Keep the same approach in eBPF and introduce the new helper
bpf_ima_file_hash() to take advantage of the modified behavior of
ima_file_hash().

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
include/uapi/linux/bpf.h | 11 +++++++++++
kernel/bpf/bpf_lsm.c | 20 ++++++++++++++++++++
tools/include/uapi/linux/bpf.h | 11 +++++++++++
3 files changed, 42 insertions(+)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index b0383d371b9a..87d996e954d4 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -5018,6 +5018,16 @@ union bpf_attr {
*
* Return
* The number of arguments of the traced function.
+ *
+ * long bpf_ima_file_hash(struct file *file, void *dst, u32 size)
+ * Description
+ * Returns a calculated IMA hash of the *file*.
+ * If the hash is larger than *size*, then only *size*
+ * bytes will be copied to *dst*
+ * Return
+ * The **hash_algo** is returned on success,
+ * **-EOPNOTSUP** if the hash calculation failed or **-EINVAL** if
+ * invalid arguments are passed.
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@@ -5206,6 +5216,7 @@ union bpf_attr {
FN(get_func_arg), \
FN(get_func_ret), \
FN(get_func_arg_cnt), \
+ FN(ima_file_hash), \
/* */

/* 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 9e4ecc990647..e8d27af5bbcc 100644
--- a/kernel/bpf/bpf_lsm.c
+++ b/kernel/bpf/bpf_lsm.c
@@ -99,6 +99,24 @@ static const struct bpf_func_proto bpf_ima_inode_hash_proto = {
.allowed = bpf_ima_inode_hash_allowed,
};

+BPF_CALL_3(bpf_ima_file_hash, struct file *, file, void *, dst, u32, size)
+{
+ return ima_file_hash(file, dst, size);
+}
+
+BTF_ID_LIST_SINGLE(bpf_ima_file_hash_btf_ids, struct, file)
+
+static const struct bpf_func_proto bpf_ima_file_hash_proto = {
+ .func = bpf_ima_file_hash,
+ .gpl_only = false,
+ .ret_type = RET_INTEGER,
+ .arg1_type = ARG_PTR_TO_BTF_ID,
+ .arg1_btf_id = &bpf_ima_file_hash_btf_ids[0],
+ .arg2_type = ARG_PTR_TO_UNINIT_MEM,
+ .arg3_type = ARG_CONST_SIZE,
+ .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)
{
@@ -121,6 +139,8 @@ bpf_lsm_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
return &bpf_bprm_opts_set_proto;
case BPF_FUNC_ima_inode_hash:
return prog->aux->sleepable ? &bpf_ima_inode_hash_proto : NULL;
+ case BPF_FUNC_ima_file_hash:
+ return prog->aux->sleepable ? &bpf_ima_file_hash_proto : NULL;
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 b0383d371b9a..87d996e954d4 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -5018,6 +5018,16 @@ union bpf_attr {
*
* Return
* The number of arguments of the traced function.
+ *
+ * long bpf_ima_file_hash(struct file *file, void *dst, u32 size)
+ * Description
+ * Returns a calculated IMA hash of the *file*.
+ * If the hash is larger than *size*, then only *size*
+ * bytes will be copied to *dst*
+ * Return
+ * The **hash_algo** is returned on success,
+ * **-EOPNOTSUP** if the hash calculation failed or **-EINVAL** if
+ * invalid arguments are passed.
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@@ -5206,6 +5216,7 @@ union bpf_attr {
FN(get_func_arg), \
FN(get_func_ret), \
FN(get_func_arg_cnt), \
+ FN(ima_file_hash), \
/* */

/* integer value in 'imm' field of BPF_CALL instruction selects which helper
--
2.32.0