Merge branch 'libbpf: add bpf_core_cast() helper'

Andrii Nakryiko says:

====================
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.
====================
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>

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

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;

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;

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;

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;

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;

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;

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);
@@ -29,7 +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;
 

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;

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)
 {
@@ -48,13 +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;
 }
@@ -65,7 +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;
 }
@@ -73,7 +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;