[PATCH bpf-next v2 1/2] bpf: Add bpf_lsm_set_bprm_opts helper

[KP Singh]

From: KP Singh <kpsingh@xxxxxxxxxx>

The helper allows modification of certain bits on the linux_binprm
struct starting with the secureexec bit which can be updated using the
BPF_LSM_F_BPRM_SECUREEXEC flag.

secureexec can be set by the LSM for privilege gaining executions to set
the AT_SECURE auxv for glibc.  When set, the dynamic linker disables the
use of certain environment variables (like LD_PRELOAD).

Signed-off-by: KP Singh <kpsingh@xxxxxxxxxx>
---
 include/uapi/linux/bpf.h       | 14 ++++++++++++++
 kernel/bpf/bpf_lsm.c           | 27 +++++++++++++++++++++++++++
 scripts/bpf_helpers_doc.py     |  2 ++
 tools/include/uapi/linux/bpf.h | 14 ++++++++++++++
 4 files changed, 57 insertions(+)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 162999b12790..7f1b6ba8246c 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -3787,6 +3787,14 @@ union bpf_attr {
  *		*ARG_PTR_TO_BTF_ID* of type *task_struct*.
  *	Return
  *		Pointer to the current task.
+ *
+ * long bpf_lsm_set_bprm_opts(struct linux_binprm *bprm, u64 flags)
+ *
+ *	Description
+ *		Sets certain options on the *bprm*:
+ *
+ *		**BPF_LSM_F_BPRM_SECUREEXEC** Set the secureexec bit
+ *		which sets the **AT_SECURE** auxv for glibc.
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -3948,6 +3956,7 @@ union bpf_attr {
 	FN(task_storage_get),		\
 	FN(task_storage_delete),	\
 	FN(get_current_task_btf),	\
+	FN(lsm_set_bprm_opts),		\
 	/* */
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
@@ -4119,6 +4128,11 @@ enum bpf_lwt_encap_mode {
 	BPF_LWT_ENCAP_IP,
 };
 
+/* Flags for LSM helpers */
+enum {
+	BPF_LSM_F_BPRM_SECUREEXEC	= (1ULL << 0),
+};
+
 #define __bpf_md_ptr(type, name)	\
 union {					\
 	type name;			\
diff --git a/kernel/bpf/bpf_lsm.c b/kernel/bpf/bpf_lsm.c
index 553107f4706a..31f85474a0ef 100644
--- a/kernel/bpf/bpf_lsm.c
+++ b/kernel/bpf/bpf_lsm.c
@@ -7,6 +7,7 @@
 #include <linux/filter.h>
 #include <linux/bpf.h>
 #include <linux/btf.h>
+#include <linux/binfmts.h>
 #include <linux/lsm_hooks.h>
 #include <linux/bpf_lsm.h>
 #include <linux/kallsyms.h>
@@ -51,6 +52,30 @@ int bpf_lsm_verify_prog(struct bpf_verifier_log *vlog,
 	return 0;
 }
 
+/* Mask for all the currently supported BPRM option flags */
+#define BPF_LSM_F_BRPM_OPTS_MASK	0x1ULL
+
+BPF_CALL_2(bpf_lsm_set_bprm_opts, struct linux_binprm *, bprm, u64, flags)
+{
+
+	if (flags & ~BPF_LSM_F_BRPM_OPTS_MASK)
+		return -EINVAL;
+
+	bprm->secureexec = (flags & BPF_LSM_F_BPRM_SECUREEXEC);
+	return 0;
+}
+
+BTF_ID_LIST_SINGLE(bpf_lsm_set_bprm_opts_btf_ids, struct, linux_binprm)
+
+const static struct bpf_func_proto bpf_lsm_set_bprm_opts_proto = {
+	.func		= bpf_lsm_set_bprm_opts,
+	.gpl_only	= false,
+	.ret_type	= RET_INTEGER,
+	.arg1_type	= ARG_PTR_TO_BTF_ID,
+	.arg1_btf_id	= &bpf_lsm_set_bprm_opts_btf_ids[0],
+	.arg2_type	= ARG_ANYTHING,
+};
+
 static const struct bpf_func_proto *
 bpf_lsm_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 {
@@ -71,6 +96,8 @@ bpf_lsm_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 		return &bpf_task_storage_get_proto;
 	case BPF_FUNC_task_storage_delete:
 		return &bpf_task_storage_delete_proto;
+	case BPF_FUNC_lsm_set_bprm_opts:
+		return &bpf_lsm_set_bprm_opts_proto;
 	default:
 		return tracing_prog_func_proto(func_id, prog);
 	}
diff --git a/scripts/bpf_helpers_doc.py b/scripts/bpf_helpers_doc.py
index 31484377b8b1..c5bc947a70ad 100755
--- a/scripts/bpf_helpers_doc.py
+++ b/scripts/bpf_helpers_doc.py
@@ -418,6 +418,7 @@ class PrinterHelpers(Printer):
             'struct bpf_tcp_sock',
             'struct bpf_tunnel_key',
             'struct bpf_xfrm_state',
+            'struct linux_binprm',
             'struct pt_regs',
             'struct sk_reuseport_md',
             'struct sockaddr',
@@ -465,6 +466,7 @@ class PrinterHelpers(Printer):
             'struct bpf_tcp_sock',
             'struct bpf_tunnel_key',
             'struct bpf_xfrm_state',
+            'struct linux_binprm',
             'struct pt_regs',
             'struct sk_reuseport_md',
             'struct sockaddr',
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 162999b12790..7f1b6ba8246c 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -3787,6 +3787,14 @@ union bpf_attr {
  *		*ARG_PTR_TO_BTF_ID* of type *task_struct*.
  *	Return
  *		Pointer to the current task.
+ *
+ * long bpf_lsm_set_bprm_opts(struct linux_binprm *bprm, u64 flags)
+ *
+ *	Description
+ *		Sets certain options on the *bprm*:
+ *
+ *		**BPF_LSM_F_BPRM_SECUREEXEC** Set the secureexec bit
+ *		which sets the **AT_SECURE** auxv for glibc.
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -3948,6 +3956,7 @@ union bpf_attr {
 	FN(task_storage_get),		\
 	FN(task_storage_delete),	\
 	FN(get_current_task_btf),	\
+	FN(lsm_set_bprm_opts),		\
 	/* */
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
@@ -4119,6 +4128,11 @@ enum bpf_lwt_encap_mode {
 	BPF_LWT_ENCAP_IP,
 };
 
+/* Flags for LSM helpers */
+enum {
+	BPF_LSM_F_BPRM_SECUREEXEC	= (1ULL << 0),
+};
+
 #define __bpf_md_ptr(type, name)	\
 union {					\
 	type name;			\
-- 
2.29.2.299.gdc1121823c-goog