[bpf-next,v4,14/15] bpf: allow all printable characters in BTF DATASEC names

Commit Message

Eduard Zingerman March 6, 2024, 10:45 a.m. UTC

The intent is to allow libbpf to use SEC("?.struct_ops") to identify
struct_ops maps that are optional, e.g. like in the following BPF code:

    SEC("?.struct_ops")
    struct test_ops optional_map = { ... };

Which yields the following BTF:

    ...
    [13] DATASEC '?.struct_ops' size=0 vlen=...
    ...

To load such BTF libbpf rewrites DATASEC name before load.
After this patch the rewrite won't be necessary.

Signed-off-by: Eduard Zingerman <[e-mail]>
---
 kernel/bpf/btf.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

Comments

Andrii Nakryiko March 6, 2024, 7:17 p.m. UTC | #1

On Wed, Mar 6, 2024 at 2:45 AM Eduard Zingerman <[e-mail]> wrote:
>
> The intent is to allow libbpf to use SEC("?.struct_ops") to identify
> struct_ops maps that are optional, e.g. like in the following BPF code:
>
>     SEC("?.struct_ops")
>     struct test_ops optional_map = { ... };
>
> Which yields the following BTF:
>
>     ...
>     [13] DATASEC '?.struct_ops' size=0 vlen=...
>     ...
>
> To load such BTF libbpf rewrites DATASEC name before load.
> After this patch the rewrite won't be necessary.
>
> Signed-off-by: Eduard Zingerman <[e-mail]>
> ---
>  kernel/bpf/btf.c | 16 +++++++++++++++-
>  1 file changed, 15 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index 6ff0bd1a91d5..170d017e8e4a 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -809,9 +809,23 @@ static bool btf_name_valid_identifier(const struct btf *btf, u32 offset)
>         return __btf_name_valid(btf, offset);

We should just rename __btf_name_valid() into
btf_name_valid_indentifier() and use that everywhere. Please consider
a clean up patch as a follow up, thanks!

>  }
>
> +/* Allow any printable character in DATASEC names */
>  static bool btf_name_valid_section(const struct btf *btf, u32 offset)
>  {
> -       return __btf_name_valid(btf, offset);
> +       /* offset must be valid */
> +       const char *src = btf_str_by_offset(btf, offset);
> +       const char *src_limit;
> +
> +       /* set a limit on identifier length */
> +       src_limit = src + KSYM_NAME_LEN;
> +       src++;
> +       while (*src && src < src_limit) {
> +               if (!isprint(*src))
> +                       return false;
> +               src++;
> +       }
> +
> +       return !*src;
>  }
>
>  static const char *__btf_name_by_offset(const struct btf *btf, u32 offset)
> --
> 2.43.0
>

Patch

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 6ff0bd1a91d5..170d017e8e4a 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -809,9 +809,23 @@  static bool btf_name_valid_identifier(const struct btf *btf, u32 offset)
 	return __btf_name_valid(btf, offset);
 }
 
+/* Allow any printable character in DATASEC names */
 static bool btf_name_valid_section(const struct btf *btf, u32 offset)
 {
-	return __btf_name_valid(btf, offset);
+	/* offset must be valid */
+	const char *src = btf_str_by_offset(btf, offset);
+	const char *src_limit;
+
+	/* set a limit on identifier length */
+	src_limit = src + KSYM_NAME_LEN;
+	src++;
+	while (*src && src < src_limit) {
+		if (!isprint(*src))
+			return false;
+		src++;
+	}
+
+	return !*src;
 }
 
 static const char *__btf_name_by_offset(const struct btf *btf, u32 offset)