[PATCH bpf-next 0/2] libbpf: add bpf_core_cast() helper

[PATCH bpf-next 0/2] libbpf: add bpf_core_cast() helper

[Andrii Nakryiko]

Add bpf_core_cast(<ptr>, <type>) macro wrapper around bpf_rdonly_cast() kfunc
to make it easier to use this functionality in BPF code. See patch #2 for
BPF selftests conversions demonstrating improvements in code succinctness.

Andrii Nakryiko (2):
  libbpf: add bpf_core_cast() macro
  selftests/bpf: convert bpf_rdonly_cast() uses to bpf_core_cast() macro

 tools/lib/bpf/bpf_core_read.h                       | 13 +++++++++++++
 tools/testing/selftests/bpf/bpf_kfuncs.h            |  2 +-
 .../testing/selftests/bpf/progs/connect_unix_prog.c |  3 +--
 .../selftests/bpf/progs/getpeername_unix_prog.c     |  3 +--
 .../selftests/bpf/progs/getsockname_unix_prog.c     |  3 +--
 .../testing/selftests/bpf/progs/recvmsg_unix_prog.c |  3 +--
 .../testing/selftests/bpf/progs/sendmsg_unix_prog.c |  3 +--
 .../selftests/bpf/progs/sk_storage_omem_uncharge.c  |  4 +---
 tools/testing/selftests/bpf/progs/sock_iter_batch.c |  4 ++--
 tools/testing/selftests/bpf/progs/type_cast.c       | 13 +++++--------
 10 files changed, 27 insertions(+), 24 deletions(-)

-- 
2.34.1

[PATCH bpf-next 1/2] libbpf: add bpf_core_cast() macro

[Andrii Nakryiko]

Add bpf_core_cast() macro that wraps bpf_rdonly_cast() kfunc. It's more
ergonomic than kfunc, as it automatically extracts btf_id with
bpf_core_type_id_kernel(), and works with type names. It also casts result
to (T *) pointer. See the definition of the macro, it's self-explanatory.

libbpf declares bpf_rdonly_cast() extern as __weak __ksym and should be
safe to not conflict with other possible declarations in user code.

But we do have a conflict with current BPF selftests that declare their
externs with first argument as `void *obj`, while libbpf opts into more
permissive `const void *obj`. This causes conflict, so we fix up BPF
selftests uses in the same patch.

Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 tools/lib/bpf/bpf_core_read.h                       | 13 +++++++++++++
 tools/testing/selftests/bpf/bpf_kfuncs.h            |  2 +-
 .../selftests/bpf/progs/sk_storage_omem_uncharge.c  |  2 --
 tools/testing/selftests/bpf/progs/type_cast.c       |  4 +---
 4 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/tools/lib/bpf/bpf_core_read.h b/tools/lib/bpf/bpf_core_read.h
index 5aec301e9585..0d3e88bd7d5f 100644
--- a/tools/lib/bpf/bpf_core_read.h
+++ b/tools/lib/bpf/bpf_core_read.h
@@ -2,6 +2,8 @@
 #ifndef __BPF_CORE_READ_H__
 #define __BPF_CORE_READ_H__
 
+#include <bpf/bpf_helpers.h>
+
 /*
  * enum bpf_field_info_kind is passed as a second argument into
  * __builtin_preserve_field_info() built-in to get a specific aspect of
@@ -292,6 +294,17 @@ enum bpf_enum_value_kind {
 #define bpf_core_read_user_str(dst, sz, src)				    \
 	bpf_probe_read_user_str(dst, sz, (const void *)__builtin_preserve_access_index(src))
 
+extern void *bpf_rdonly_cast(const void *obj, __u32 btf_id) __ksym __weak;
+
+/*
+ * Cast provided pointer *ptr* into a pointer to a specified *type* in such
+ * a way that BPF verifier will become aware of associated kernel-side BTF
+ * type. This allows to access members of kernel types directly without the
+ * need to use BPF_CORE_READ() macros.
+ */
+#define bpf_core_cast(ptr, type)					    \
+	((typeof(type) *)bpf_rdonly_cast((ptr), bpf_core_type_id_kernel(type)))
+
 #define ___concat(a, b) a ## b
 #define ___apply(fn, n) ___concat(fn, n)
 #define ___nth(_1, _2, _3, _4, _5, _6, _7, _8, _9, _10, __11, N, ...) N
diff --git a/tools/testing/selftests/bpf/bpf_kfuncs.h b/tools/testing/selftests/bpf/bpf_kfuncs.h
index 23c24f852f4f..0cd4111f954c 100644
--- a/tools/testing/selftests/bpf/bpf_kfuncs.h
+++ b/tools/testing/selftests/bpf/bpf_kfuncs.h
@@ -63,7 +63,7 @@ extern int bpf_sk_assign_tcp_reqsk(struct __sk_buff *skb, struct sock *sk,
 
 void *bpf_cast_to_kern_ctx(void *) __ksym;
 
-void *bpf_rdonly_cast(void *obj, __u32 btf_id) __ksym;
+extern void *bpf_rdonly_cast(const void *obj, __u32 btf_id) __ksym __weak;
 
 extern int bpf_get_file_xattr(struct file *file, const char *name,
 			      struct bpf_dynptr *value_ptr) __ksym;
diff --git a/tools/testing/selftests/bpf/progs/sk_storage_omem_uncharge.c b/tools/testing/selftests/bpf/progs/sk_storage_omem_uncharge.c
index 3e745793b27a..934c4e5ada5b 100644
--- a/tools/testing/selftests/bpf/progs/sk_storage_omem_uncharge.c
+++ b/tools/testing/selftests/bpf/progs/sk_storage_omem_uncharge.c
@@ -12,8 +12,6 @@ int cookie_found = 0;
 __u64 cookie = 0;
 __u32 omem = 0;
 
-void *bpf_rdonly_cast(void *, __u32) __ksym;
-
 struct {
 	__uint(type, BPF_MAP_TYPE_SK_STORAGE);
 	__uint(map_flags, BPF_F_NO_PREALLOC);
diff --git a/tools/testing/selftests/bpf/progs/type_cast.c b/tools/testing/selftests/bpf/progs/type_cast.c
index a9629ac230fd..98ab35893f51 100644
--- a/tools/testing/selftests/bpf/progs/type_cast.c
+++ b/tools/testing/selftests/bpf/progs/type_cast.c
@@ -4,6 +4,7 @@
 #include <bpf/bpf_helpers.h>
 #include <bpf/bpf_tracing.h>
 #include <bpf/bpf_core_read.h>
+#include "bpf_kfuncs.h"
 
 struct {
 	__uint(type, BPF_MAP_TYPE_TASK_STORAGE);
@@ -19,9 +20,6 @@ char name[IFNAMSIZ];
 unsigned int inum;
 unsigned int meta_len, frag0_len, kskb_len, kskb2_len;
 
-void *bpf_cast_to_kern_ctx(void *) __ksym;
-void *bpf_rdonly_cast(void *, __u32) __ksym;
-
 SEC("?xdp")
 int md_xdp(struct xdp_md *ctx)
 {
-- 
2.34.1

[PATCH bpf-next 2/2] selftests/bpf: convert bpf_rdonly_cast() uses to bpf_core_cast() macro

[Andrii Nakryiko]

Use more ergonomic bpf_core_cast() macro instead of bpf_rdonly_cast() in
selftests code.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 tools/testing/selftests/bpf/progs/connect_unix_prog.c    | 3 +--
 .../testing/selftests/bpf/progs/getpeername_unix_prog.c  | 3 +--
 .../testing/selftests/bpf/progs/getsockname_unix_prog.c  | 3 +--
 tools/testing/selftests/bpf/progs/recvmsg_unix_prog.c    | 3 +--
 tools/testing/selftests/bpf/progs/sendmsg_unix_prog.c    | 3 +--
 .../selftests/bpf/progs/sk_storage_omem_uncharge.c       | 2 +-
 tools/testing/selftests/bpf/progs/sock_iter_batch.c      | 4 ++--
 tools/testing/selftests/bpf/progs/type_cast.c            | 9 ++++-----
 8 files changed, 12 insertions(+), 18 deletions(-)

diff --git a/tools/testing/selftests/bpf/progs/connect_unix_prog.c b/tools/testing/selftests/bpf/progs/connect_unix_prog.c
index ca8aa2f116b3..2ef0e0c46d17 100644
--- a/tools/testing/selftests/bpf/progs/connect_unix_prog.c
+++ b/tools/testing/selftests/bpf/progs/connect_unix_prog.c
@@ -28,8 +28,7 @@ int connect_unix_prog(struct bpf_sock_addr *ctx)
 	if (sa_kern->uaddrlen != unaddrlen)
 		return 0;
 
-	sa_kern_unaddr = bpf_rdonly_cast(sa_kern->uaddr,
-						bpf_core_type_id_kernel(struct sockaddr_un));
+	sa_kern_unaddr = bpf_core_cast(sa_kern->uaddr, struct sockaddr_un);
 	if (memcmp(sa_kern_unaddr->sun_path, SERVUN_REWRITE_ADDRESS,
 			sizeof(SERVUN_REWRITE_ADDRESS) - 1) != 0)
 		return 0;
diff --git a/tools/testing/selftests/bpf/progs/getpeername_unix_prog.c b/tools/testing/selftests/bpf/progs/getpeername_unix_prog.c
index 9c078f34bbb2..5a76754f846b 100644
--- a/tools/testing/selftests/bpf/progs/getpeername_unix_prog.c
+++ b/tools/testing/selftests/bpf/progs/getpeername_unix_prog.c
@@ -27,8 +27,7 @@ int getpeername_unix_prog(struct bpf_sock_addr *ctx)
 	if (sa_kern->uaddrlen != unaddrlen)
 		return 1;
 
-	sa_kern_unaddr = bpf_rdonly_cast(sa_kern->uaddr,
-						bpf_core_type_id_kernel(struct sockaddr_un));
+	sa_kern_unaddr = bpf_core_cast(sa_kern->uaddr, struct sockaddr_un);
 	if (memcmp(sa_kern_unaddr->sun_path, SERVUN_REWRITE_ADDRESS,
 			sizeof(SERVUN_REWRITE_ADDRESS) - 1) != 0)
 		return 1;
diff --git a/tools/testing/selftests/bpf/progs/getsockname_unix_prog.c b/tools/testing/selftests/bpf/progs/getsockname_unix_prog.c
index ac7145111497..7867113c696f 100644
--- a/tools/testing/selftests/bpf/progs/getsockname_unix_prog.c
+++ b/tools/testing/selftests/bpf/progs/getsockname_unix_prog.c
@@ -27,8 +27,7 @@ int getsockname_unix_prog(struct bpf_sock_addr *ctx)
 	if (sa_kern->uaddrlen != unaddrlen)
 		return 1;
 
-	sa_kern_unaddr = bpf_rdonly_cast(sa_kern->uaddr,
-						bpf_core_type_id_kernel(struct sockaddr_un));
+	sa_kern_unaddr = bpf_core_cast(sa_kern->uaddr, struct sockaddr_un);
 	if (memcmp(sa_kern_unaddr->sun_path, SERVUN_REWRITE_ADDRESS,
 			sizeof(SERVUN_REWRITE_ADDRESS) - 1) != 0)
 		return 1;
diff --git a/tools/testing/selftests/bpf/progs/recvmsg_unix_prog.c b/tools/testing/selftests/bpf/progs/recvmsg_unix_prog.c
index 4dfbc8552558..1c7ab44bccfa 100644
--- a/tools/testing/selftests/bpf/progs/recvmsg_unix_prog.c
+++ b/tools/testing/selftests/bpf/progs/recvmsg_unix_prog.c
@@ -27,8 +27,7 @@ int recvmsg_unix_prog(struct bpf_sock_addr *ctx)
 	if (sa_kern->uaddrlen != unaddrlen)
 		return 1;
 
-	sa_kern_unaddr = bpf_rdonly_cast(sa_kern->uaddr,
-						bpf_core_type_id_kernel(struct sockaddr_un));
+	sa_kern_unaddr = bpf_core_cast(sa_kern->uaddr, struct sockaddr_un);
 	if (memcmp(sa_kern_unaddr->sun_path, SERVUN_ADDRESS,
 			sizeof(SERVUN_ADDRESS) - 1) != 0)
 		return 1;
diff --git a/tools/testing/selftests/bpf/progs/sendmsg_unix_prog.c b/tools/testing/selftests/bpf/progs/sendmsg_unix_prog.c
index 1f67e832666e..d8869b03dda9 100644
--- a/tools/testing/selftests/bpf/progs/sendmsg_unix_prog.c
+++ b/tools/testing/selftests/bpf/progs/sendmsg_unix_prog.c
@@ -28,8 +28,7 @@ int sendmsg_unix_prog(struct bpf_sock_addr *ctx)
 	if (sa_kern->uaddrlen != unaddrlen)
 		return 0;
 
-	sa_kern_unaddr = bpf_rdonly_cast(sa_kern->uaddr,
-						bpf_core_type_id_kernel(struct sockaddr_un));
+	sa_kern_unaddr = bpf_core_cast(sa_kern->uaddr, struct sockaddr_un);
 	if (memcmp(sa_kern_unaddr->sun_path, SERVUN_REWRITE_ADDRESS,
 			sizeof(SERVUN_REWRITE_ADDRESS) - 1) != 0)
 		return 0;
diff --git a/tools/testing/selftests/bpf/progs/sk_storage_omem_uncharge.c b/tools/testing/selftests/bpf/progs/sk_storage_omem_uncharge.c
index 934c4e5ada5b..46d6eb2a3b17 100644
--- a/tools/testing/selftests/bpf/progs/sk_storage_omem_uncharge.c
+++ b/tools/testing/selftests/bpf/progs/sk_storage_omem_uncharge.c
@@ -27,7 +27,7 @@ int BPF_PROG(bpf_local_storage_destroy, struct bpf_local_storage *local_storage)
 	if (local_storage_ptr != local_storage)
 		return 0;
 
-	sk = bpf_rdonly_cast(sk_ptr, bpf_core_type_id_kernel(struct sock));
+	sk = bpf_core_cast(sk_ptr, struct sock);
 	if (sk->sk_cookie.counter != cookie)
 		return 0;
 
diff --git a/tools/testing/selftests/bpf/progs/sock_iter_batch.c b/tools/testing/selftests/bpf/progs/sock_iter_batch.c
index ffbbfe1fa1c1..96531b0d9d55 100644
--- a/tools/testing/selftests/bpf/progs/sock_iter_batch.c
+++ b/tools/testing/selftests/bpf/progs/sock_iter_batch.c
@@ -32,7 +32,7 @@ int iter_tcp_soreuse(struct bpf_iter__tcp *ctx)
 	if (!sk)
 		return 0;
 
-	sk = bpf_rdonly_cast(sk, bpf_core_type_id_kernel(struct sock));
+	sk = bpf_core_cast(sk, struct sock);
 	if (sk->sk_family != AF_INET6 ||
 	    sk->sk_state != TCP_LISTEN ||
 	    !ipv6_addr_loopback(&sk->sk_v6_rcv_saddr))
@@ -68,7 +68,7 @@ int iter_udp_soreuse(struct bpf_iter__udp *ctx)
 	if (!sk)
 		return 0;
 
-	sk = bpf_rdonly_cast(sk, bpf_core_type_id_kernel(struct sock));
+	sk = bpf_core_cast(sk, struct sock);
 	if (sk->sk_family != AF_INET6 ||
 	    !ipv6_addr_loopback(&sk->sk_v6_rcv_saddr))
 		return 0;
diff --git a/tools/testing/selftests/bpf/progs/type_cast.c b/tools/testing/selftests/bpf/progs/type_cast.c
index 98ab35893f51..9d808b8f4ab0 100644
--- a/tools/testing/selftests/bpf/progs/type_cast.c
+++ b/tools/testing/selftests/bpf/progs/type_cast.c
@@ -46,13 +46,12 @@ int md_skb(struct __sk_buff *skb)
 	/* Simulate the following kernel macro:
 	 *   #define skb_shinfo(SKB) ((struct skb_shared_info *)(skb_end_pointer(SKB)))
 	 */
-	shared_info = bpf_rdonly_cast(kskb->head + kskb->end,
-		bpf_core_type_id_kernel(struct skb_shared_info));
+	shared_info = bpf_core_cast(kskb->head + kskb->end, struct skb_shared_info);
 	meta_len = shared_info->meta_len;
 	frag0_len = shared_info->frag_list->len;
 
 	/* kskb2 should be equal to kskb */
-	kskb2 = bpf_rdonly_cast(kskb, bpf_core_type_id_kernel(struct sk_buff));
+	kskb2 = bpf_core_cast(kskb, typeof(*kskb2));
 	kskb2_len = kskb2->len;
 	return 0;
 }
@@ -63,7 +62,7 @@ int BPF_PROG(untrusted_ptr, struct pt_regs *regs, long id)
 	struct task_struct *task, *task_dup;
 
 	task = bpf_get_current_task_btf();
-	task_dup = bpf_rdonly_cast(task, bpf_core_type_id_kernel(struct task_struct));
+	task_dup = bpf_core_cast(task, struct task_struct);
 	(void)bpf_task_storage_get(&enter_id, task_dup, 0, 0);
 	return 0;
 }
@@ -71,7 +70,7 @@ int BPF_PROG(untrusted_ptr, struct pt_regs *regs, long id)
 SEC("?tracepoint/syscalls/sys_enter_nanosleep")
 int kctx_u64(void *ctx)
 {
-	u64 *kctx = bpf_rdonly_cast(ctx, bpf_core_type_id_kernel(u64));
+	u64 *kctx = bpf_core_cast(ctx, u64);
 
 	(void)kctx;
 	return 0;
-- 
2.34.1

Re: [PATCH bpf-next 0/2] libbpf: add bpf_core_cast() helper

[patchwork-bot+netdevbpf]

Hello:

This series was applied to bpf/bpf-next.git (master)
by Martin KaFai Lau <martin.lau@kernel.org>:

On Tue, 30 Jan 2024 13:20:21 -0800 you wrote:
> Add bpf_core_cast(<ptr>, <type>) macro wrapper around bpf_rdonly_cast() kfunc
> to make it easier to use this functionality in BPF code. See patch #2 for
> BPF selftests conversions demonstrating improvements in code succinctness.
> 
> Andrii Nakryiko (2):
>   libbpf: add bpf_core_cast() macro
>   selftests/bpf: convert bpf_rdonly_cast() uses to bpf_core_cast() macro
> 
> [...]

Here is the summary with links:
  - [bpf-next,1/2] libbpf: add bpf_core_cast() macro
    https://git.kernel.org/bpf/bpf-next/c/20d59ee55172
  - [bpf-next,2/2] selftests/bpf: convert bpf_rdonly_cast() uses to bpf_core_cast() macro
    https://git.kernel.org/bpf/bpf-next/c/ea9d561686fb

You are awesome, thank you!
-- 
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