bpf: Introduce bpf_arch_text_copy

This will be used to copy JITed text to RO protected module memory. On
x86, bpf_arch_text_copy is implemented with text_poke_copy.

bpf_arch_text_copy returns pointer to dst on success, and ERR_PTR(errno)
on errors.
Signed-off-by: Song Liu <song@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20220204185742.271030-7-song@kernel.org

arch/x86/net/bpf_jit_comp.c

@@ -2412,3 +2412,10 @@ bool bpf_jit_supports_kfunc_call(void)
 {
 	return true;
 }
+
+void *bpf_arch_text_copy(void *dst, void *src, size_t len)
+{
+	if (text_poke_copy(dst, src, len) == NULL)
+		return ERR_PTR(-EINVAL);
+	return dst;
+}

include/linux/bpf.h

@@ -2362,6 +2362,8 @@ enum bpf_text_poke_type {
 int bpf_arch_text_poke(void *ip, enum bpf_text_poke_type t,
 		       void *addr1, void *addr2);
 
+void *bpf_arch_text_copy(void *dst, void *src, size_t len);
+
 struct btf_id_set;
 bool btf_id_set_contains(const struct btf_id_set *set, u32 id);
 

kernel/bpf/core.c

@@ -2440,6 +2440,11 @@ int __weak bpf_arch_text_poke(void *ip, enum bpf_text_poke_type t,
 	return -ENOTSUPP;
 }
 
+void * __weak bpf_arch_text_copy(void *dst, void *src, size_t len)
+{
+	return ERR_PTR(-ENOTSUPP);
+}
+
 DEFINE_STATIC_KEY_FALSE(bpf_stats_enabled_key);
 EXPORT_SYMBOL(bpf_stats_enabled_key);