Commit 03b77e17 authored by Alexei Starovoitov's avatar Alexei Starovoitov Committed by Daniel Borkmann
Browse files

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: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Acked-by: default avatarDavid Vernet <void@manifault.com>
Link: https://lore.kernel.org/bpf/20230303041446.3630-2-alexei.starovoitov@gmail.com
parent 944459e8

Documentation/bpf/bpf_design_QA.rst

+2 −2
Original line number Diff line number Diff line
@@ -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

+2 −2
Original line number Diff line number Diff line
@@ -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

+1 −1
Original line number Diff line number Diff line
@@ -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

+2 −2
Original line number Diff line number Diff line
@@ -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

+1 −1
Original line number Diff line number Diff line
@@ -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