bpf: Rename __kptr_ref -> __kptr and __kptr -> __kptr_untrusted.

__kptr meant to store PTR_UNTRUSTED kernel pointers inside bpf maps.
The concept felt useful, but didn't get much traction,
since bpf_rdonly_cast() was added soon after and bpf programs received
a simpler way to access PTR_UNTRUSTED kernel pointers
without going through restrictive __kptr usage.

Rename __kptr_ref -> __kptr and __kptr -> __kptr_untrusted to indicate
its intended usage.
The main goal of __kptr_untrusted was to read/write such pointers
directly while bpf_kptr_xchg was a mechanism to access refcnted
kernel pointers. The next patch will allow RCU protected __kptr access
with direct read. At that point __kptr_untrusted will be deprecated.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: David Vernet <void@manifault.com>
Link: https://lore.kernel.org/bpf/20230303041446.3630-2-alexei.starovoitov@gmail.com

Documentation/bpf/bpf_design_QA.rst

@@ -314,7 +314,7 @@ Q: What is the compatibility story for special BPF types in map values?
 Q: Users are allowed to embed bpf_spin_lock, bpf_timer fields in their BPF map
 values (when using BTF support for BPF maps). This allows to use helpers for
 such objects on these fields inside map values. Users are also allowed to embed
-pointers to some kernel types (with __kptr and __kptr_ref BTF tags). Will the
+pointers to some kernel types (with __kptr_untrusted and __kptr BTF tags). Will the
 kernel preserve backwards compatibility for these features?
 
 A: It depends. For bpf_spin_lock, bpf_timer: YES, for kptr and everything else:
@@ -324,7 +324,7 @@ For struct types that have been added already, like bpf_spin_lock and bpf_timer,
 the kernel will preserve backwards compatibility, as they are part of UAPI.
 
 For kptrs, they are also part of UAPI, but only with respect to the kptr
-mechanism. The types that you can use with a __kptr and __kptr_ref tagged
+mechanism. The types that you can use with a __kptr_untrusted and __kptr tagged
 pointer in your struct are NOT part of the UAPI contract. The supported types can
 and will change across kernel releases. However, operations like accessing kptr
 fields and bpf_kptr_xchg() helper will continue to be supported across kernel

Documentation/bpf/cpumasks.rst

@@ -51,7 +51,7 @@ For example:
 .. code-block:: c
 
         struct cpumask_map_value {
-                struct bpf_cpumask __kptr_ref * cpumask;
+                struct bpf_cpumask __kptr * cpumask;
         };
 
         struct array_map {
@@ -128,7 +128,7 @@ Here is an example of a ``struct bpf_cpumask *`` being retrieved from a map:
 
 	/* struct containing the struct bpf_cpumask kptr which is stored in the map. */
 	struct cpumasks_kfunc_map_value {
-		struct bpf_cpumask __kptr_ref * bpf_cpumask;
+		struct bpf_cpumask __kptr * bpf_cpumask;
 	};
 
 	/* The map containing struct cpumasks_kfunc_map_value entries. */

Documentation/bpf/kfuncs.rst

@@ -544,7 +544,7 @@ Here's an example of how it can be used:
 
 	/* struct containing the struct task_struct kptr which is actually stored in the map. */
 	struct __cgroups_kfunc_map_value {
-		struct cgroup __kptr_ref * cgroup;
+		struct cgroup __kptr * cgroup;
 	};
 
 	/* The map containing struct __cgroups_kfunc_map_value entries. */

kernel/bpf/btf.c

@@ -3288,9 +3288,9 @@ static int btf_find_kptr(const struct btf *btf, const struct btf_type *t,
 	/* Reject extra tags */
 	if (btf_type_is_type_tag(btf_type_by_id(btf, t->type)))
 		return -EINVAL;
-	if (!strcmp("kptr", __btf_name_by_offset(btf, t->name_off)))
+	if (!strcmp("kptr_untrusted", __btf_name_by_offset(btf, t->name_off)))
 		type = BPF_KPTR_UNREF;
-	else if (!strcmp("kptr_ref", __btf_name_by_offset(btf, t->name_off)))
+	else if (!strcmp("kptr", __btf_name_by_offset(btf, t->name_off)))
 		type = BPF_KPTR_REF;
 	else
 		return -EINVAL;

tools/lib/bpf/bpf_helpers.h

@@ -174,8 +174,8 @@ enum libbpf_tristate {
 
 #define __kconfig __attribute__((section(".kconfig")))
 #define __ksym __attribute__((section(".ksyms")))
+#define __kptr_untrusted __attribute__((btf_type_tag("kptr_untrusted")))
 #define __kptr __attribute__((btf_type_tag("kptr")))
-#define __kptr_ref __attribute__((btf_type_tag("kptr_ref")))
 
 #ifndef ___bpf_concat
 #define ___bpf_concat(a, b) a ## b

tools/testing/selftests/bpf/progs/cb_refs.c

@@ -4,7 +4,7 @@
 #include <bpf/bpf_helpers.h>
 
 struct map_value {
-	struct prog_test_ref_kfunc __kptr_ref *ptr;
+	struct prog_test_ref_kfunc __kptr *ptr;
 };
 
 struct {

tools/testing/selftests/bpf/progs/cgrp_kfunc_common.h

@@ -10,7 +10,7 @@
 #include <bpf/bpf_tracing.h>
 
 struct __cgrps_kfunc_map_value {
-	struct cgroup __kptr_ref * cgrp;
+	struct cgroup __kptr * cgrp;
 };
 
 struct hash_map {

tools/testing/selftests/bpf/progs/cpumask_common.h

@@ -10,7 +10,7 @@
 int err;
 
 struct __cpumask_map_value {
-	struct bpf_cpumask __kptr_ref * cpumask;
+	struct bpf_cpumask __kptr * cpumask;
 };
 
 struct array_map {

tools/testing/selftests/bpf/progs/jit_probe_mem.c

@@ -4,7 +4,7 @@
 #include <bpf/bpf_tracing.h>
 #include <bpf/bpf_helpers.h>
 
-static struct prog_test_ref_kfunc __kptr_ref *v;
+static struct prog_test_ref_kfunc __kptr *v;
 long total_sum = -1;
 
 extern struct prog_test_ref_kfunc *bpf_kfunc_call_test_acquire(unsigned long *sp) __ksym;

tools/testing/selftests/bpf/progs/lru_bug.c

@@ -4,7 +4,7 @@
 #include <bpf/bpf_helpers.h>
 
 struct map_value {
-	struct task_struct __kptr *ptr;
+	struct task_struct __kptr_untrusted *ptr;
 };
 
 struct {

tools/testing/selftests/bpf/progs/map_kptr.c

@@ -4,8 +4,8 @@
 #include <bpf/bpf_helpers.h>
 
 struct map_value {
-	struct prog_test_ref_kfunc __kptr *unref_ptr;
-	struct prog_test_ref_kfunc __kptr_ref *ref_ptr;
+	struct prog_test_ref_kfunc __kptr_untrusted *unref_ptr;
+	struct prog_test_ref_kfunc __kptr *ref_ptr;
 };
 
 struct array_map {

tools/testing/selftests/bpf/progs/map_kptr_fail.c

@@ -7,9 +7,9 @@
 
 struct map_value {
 	char buf[8];
-	struct prog_test_ref_kfunc __kptr *unref_ptr;
-	struct prog_test_ref_kfunc __kptr_ref *ref_ptr;
-	struct prog_test_member __kptr_ref *ref_memb_ptr;
+	struct prog_test_ref_kfunc __kptr_untrusted *unref_ptr;
+	struct prog_test_ref_kfunc __kptr *ref_ptr;
+	struct prog_test_member __kptr *ref_memb_ptr;
 };
 
 struct array_map {

tools/testing/selftests/bpf/progs/task_kfunc_common.h

@@ -10,7 +10,7 @@
 #include <bpf/bpf_tracing.h>
 
 struct __tasks_kfunc_map_value {
-	struct task_struct __kptr_ref * task;
+	struct task_struct __kptr * task;
 };
 
 struct hash_map {

tools/testing/selftests/bpf/test_verifier.c

@@ -699,13 +699,13 @@ static int create_cgroup_storage(bool percpu)
  *   struct bpf_timer t;
  * };
  * struct btf_ptr {
+ *   struct prog_test_ref_kfunc __kptr_untrusted *ptr;
  *   struct prog_test_ref_kfunc __kptr *ptr;
- *   struct prog_test_ref_kfunc __kptr_ref *ptr;
- *   struct prog_test_member __kptr_ref *ptr;
+ *   struct prog_test_member __kptr *ptr;
  * }
  */
 static const char btf_str_sec[] = "\0bpf_spin_lock\0val\0cnt\0l\0bpf_timer\0timer\0t"
-				  "\0btf_ptr\0prog_test_ref_kfunc\0ptr\0kptr\0kptr_ref"
+				  "\0btf_ptr\0prog_test_ref_kfunc\0ptr\0kptr\0kptr_untrusted"
 				  "\0prog_test_member";
 static __u32 btf_raw_types[] = {
 	/* int */
@@ -724,20 +724,20 @@ static __u32 btf_raw_types[] = {
 	BTF_MEMBER_ENC(41, 4, 0), /* struct bpf_timer t; */
 	/* struct prog_test_ref_kfunc */		/* [6] */
 	BTF_STRUCT_ENC(51, 0, 0),
-	BTF_STRUCT_ENC(89, 0, 0),			/* [7] */
+	BTF_STRUCT_ENC(95, 0, 0),			/* [7] */
+	/* type tag "kptr_untrusted" */
+	BTF_TYPE_TAG_ENC(80, 6),			/* [8] */
 	/* type tag "kptr" */
-	BTF_TYPE_TAG_ENC(75, 6),			/* [8] */
-	/* type tag "kptr_ref" */
-	BTF_TYPE_TAG_ENC(80, 6),			/* [9] */
-	BTF_TYPE_TAG_ENC(80, 7),			/* [10] */
+	BTF_TYPE_TAG_ENC(75, 6),			/* [9] */
+	BTF_TYPE_TAG_ENC(75, 7),			/* [10] */
 	BTF_PTR_ENC(8),					/* [11] */
 	BTF_PTR_ENC(9),					/* [12] */
 	BTF_PTR_ENC(10),				/* [13] */
 	/* struct btf_ptr */				/* [14] */
 	BTF_STRUCT_ENC(43, 3, 24),
-	BTF_MEMBER_ENC(71, 11, 0), /* struct prog_test_ref_kfunc __kptr *ptr; */
-	BTF_MEMBER_ENC(71, 12, 64), /* struct prog_test_ref_kfunc __kptr_ref *ptr; */
-	BTF_MEMBER_ENC(71, 13, 128), /* struct prog_test_member __kptr_ref *ptr; */
+	BTF_MEMBER_ENC(71, 11, 0), /* struct prog_test_ref_kfunc __kptr_untrusted *ptr; */
+	BTF_MEMBER_ENC(71, 12, 64), /* struct prog_test_ref_kfunc __kptr *ptr; */
+	BTF_MEMBER_ENC(71, 13, 128), /* struct prog_test_member __kptr *ptr; */
 };
 
 static char bpf_vlog[UINT_MAX >> 8];