bpf: Allow names of Rust types and functions in BTF

Names of types and functions in BTF that LLVM makes for a Rust program
are not C identifiers:

  [69] STRUCT 'NonNull<str>' size=16 vlen=1
  [147] FUNC 'write_fmt<scx_cosmos::BpfStream>' type_id=146

and the kernel rejects such BTF with "Invalid name". scx_simple and
scx_cosmos schedulers written in Rust have them in STRUCT, FWD and FUNC,
made of letters, digits and " #&()*,:;<>[]{}", 430 characters at most.

Allow any printable character in btf_name_valid_identifier(), like it's
done for DATASEC. It checks names of types, functions, members,
enumerators, variables and arguments, so all of them can have such
characters now. The limit of KSYM_NAME_LEN stays.

The name of FUNC is a part of the name of the program in kallsyms, where
a space would break the parsers. Replace what is not a character of
an identifier with '_' there.

Tests in prog_tests/btf.c expect "Invalid name" for names with '!' and
'*', which are valid now. Put a character that is not printable there.
The type name '?foo' is expected to load.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20261002124714.180012-6-alexei.starovoitov@gmail.com
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>

2 files changed, 8 insertions, 12 deletions

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 8cc17a1cd25c..d27af5d8e495 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -901,16 +901,6 @@ static bool btf_name_offset_valid(const struct btf *btf, u32 offset)
 	return offset < btf->hdr.str_len;
 }
 
-static bool __btf_name_char_ok(char c, bool first)
-{
-	if ((first ? !isalpha(c) :
-		     !isalnum(c)) &&
-	    c != '_' &&
-	    c != '.')
-		return false;
-	return true;
-}
-
 const char *btf_str_by_offset(const struct btf *btf, u32 offset)
 {
 	while (offset < btf->start_str_off)
@@ -923,20 +913,21 @@ const char *btf_str_by_offset(const struct btf *btf, u32 offset)
 	return NULL;
 }
 
+/* Names in BTF of Rust are not C identifiers. Allow any printable character */
 static bool btf_name_valid_identifier(const struct btf *btf, u32 offset)
 {
 	/* offset must be valid */
 	const char *src = btf_str_by_offset(btf, offset);
 	const char *src_limit;
 
-	if (!__btf_name_char_ok(*src, true))
+	if (!isprint(*src))
 		return false;
 
 	/* set a limit on identifier length */
 	src_limit = src + KSYM_NAME_LEN;
 	src++;
 	while (*src && src < src_limit) {
-		if (!__btf_name_char_ok(*src, false))
+		if (!isprint(*src))
 			return false;
 		src++;
 	}
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 92a87c73aa44..05c89396119a 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -18,6 +18,7 @@
  */
 
 #include <uapi/linux/btf.h>
+#include <linux/ctype.h>
 #include <linux/filter.h>
 #include <linux/sched/signal.h>
 #include <linux/skbuff.h>
@@ -589,6 +590,10 @@ bpf_prog_ksym_set_name(struct bpf_prog *prog)
 				      prog->aux->func_info[prog->aux->func_idx].type_id);
 		func_name = btf_name_by_offset(prog->aux->btf, type->name_off);
 		snprintf(sym, (size_t)(end - sym), "_%s", func_name);
+		/* the name of a function of Rust is not an identifier */
+		for (; *sym; sym++)
+			if (!isalnum(*sym) && *sym != '_' && *sym != '.')
+				*sym = '_';
 		return;
 	}