Re: [PATCH v3 14/21] objtool: Prevent kCFI hashes from being decoded as instructions

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [High] Build failure due to undeclared mapping symbol functions.
- [Low] Unused header inclusion.
--

commit 4ad78a24a64cd6a2d10b9a2f9c0d306fba3e6d19
Author: Josh Poimboeuf <jpoimboe@kernel.org>

objtool: Prevent kCFI hashes from being decoded as instructions

On arm64 with CONFIG_CFI=y, Clang places a 4-byte kCFI type hash immediately
before each address-taken function entry. This commit uses mapping symbols
to mark such data as NOP in text sections to prevent objtool from decoding
them.

> diff --git a/tools/objtool/check.c b/tools/objtool/check.c
> index e05dc7a93dc1e..2b03a2d6fc952 100644
> --- a/tools/objtool/check.c
> +++ b/tools/objtool/check.c
> @@ -25,6 +25,7 @@
>  #include <linux/kernel.h>
>  #include <linux/static_call_types.h>
>  #include <linux/string.h>
> +#include <linux/kconfig.h>

This isn't a bug, but is this include needed? It doesn't appear that any
Kconfig configuration macros are being used in the modified code.

[ ... ]

> @@ -478,6 +483,16 @@ static int decode_instructions(struct objtool_file *file)
>  
>  			prev_len = insn->len;
>  
> +			/* Use mapping symbols to skip data in text sections */
> +			sec_for_each_sym_from(sec, map_sym) {
> +				if (map_sym->offset > offset)
> +					break;
> +				if (is_mapping_sym(map_sym))
> +					is_data = is_data_mapping_sym(map_sym);

Could this cause a build failure across architectures here? It appears
is_mapping_sym() and is_data_mapping_sym() are neither declared nor defined
anywhere in the codebase at this point in the patch series.

If these functions are only introduced in a subsequent commit, applying
this patch independently might result in an implicit declaration of function
error, breaking git bisectability.

> +			}
> +			if (is_data)
> +				insn->type = INSN_NOP;
> +
>  			/*

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/cover.1778642120.git.jpoimboe@kernel.org?part=14