Re: [PATCH] modpost: validate symbol names also in find_elf_symbol

[Masahiro Yamada]

On Wed, Oct 24, 2018 at 7:15 AM Sami Tolvanen <samitolvanen@xxxxxxxxxx> wrote:
>
> If an ARM mapping symbol shares an address with a valid symbol,
> find_elf_symbol can currently return the mapping symbol instead, as the
> symbol is not validated. This can result in confusing warnings:
>
>   WARNING: vmlinux.o(.text+0x18f4028): Section mismatch in reference
>   from the function set_reset_devices() to the variable .init.text:$x.0
>
> This change adds a call to is_valid_name to find_elf_symbol, similarly
> to how it's already used in find_elf_symbol2.
>
> Signed-off-by: Sami Tolvanen <samitolvanen@xxxxxxxxxx>
> ---


Applied to linux-kbuild.

Thanks!



>  scripts/mod/modpost.c | 50 ++++++++++++++++++++++---------------------
>  1 file changed, 26 insertions(+), 24 deletions(-)
>
> diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
> index 0d998c54564d..b709b2e623d6 100644
> --- a/scripts/mod/modpost.c
> +++ b/scripts/mod/modpost.c
> @@ -1204,6 +1204,30 @@ static int secref_whitelist(const struct sectioncheck *mismatch,
>         return 1;
>  }
>
> +static inline int is_arm_mapping_symbol(const char *str)
> +{
> +       return str[0] == '$' && strchr("axtd", str[1])
> +              && (str[2] == '\0' || str[2] == '.');
> +}
> +
> +/*
> + * If there's no name there, ignore it; likewise, ignore it if it's
> + * one of the magic symbols emitted used by current ARM tools.
> + *
> + * Otherwise if find_symbols_between() returns those symbols, they'll
> + * fail the whitelist tests and cause lots of false alarms ... fixable
> + * only by merging __exit and __init sections into __text, bloating
> + * the kernel (which is especially evil on embedded platforms).
> + */
> +static inline int is_valid_name(struct elf_info *elf, Elf_Sym *sym)
> +{
> +       const char *name = elf->strtab + sym->st_name;
> +
> +       if (!name || !strlen(name))
> +               return 0;
> +       return !is_arm_mapping_symbol(name);
> +}
> +
>  /**
>   * Find symbol based on relocation record info.
>   * In some cases the symbol supplied is a valid symbol so
> @@ -1229,6 +1253,8 @@ static Elf_Sym *find_elf_symbol(struct elf_info *elf, Elf64_Sword addr,
>                         continue;
>                 if (ELF_ST_TYPE(sym->st_info) == STT_SECTION)
>                         continue;
> +               if (!is_valid_name(elf, sym))
> +                       continue;
>                 if (sym->st_value == addr)
>                         return sym;
>                 /* Find a symbol nearby - addr are maybe negative */
> @@ -1247,30 +1273,6 @@ static Elf_Sym *find_elf_symbol(struct elf_info *elf, Elf64_Sword addr,
>                 return NULL;
>  }
>
> -static inline int is_arm_mapping_symbol(const char *str)
> -{
> -       return str[0] == '$' && strchr("axtd", str[1])
> -              && (str[2] == '\0' || str[2] == '.');
> -}
> -
> -/*
> - * If there's no name there, ignore it; likewise, ignore it if it's
> - * one of the magic symbols emitted used by current ARM tools.
> - *
> - * Otherwise if find_symbols_between() returns those symbols, they'll
> - * fail the whitelist tests and cause lots of false alarms ... fixable
> - * only by merging __exit and __init sections into __text, bloating
> - * the kernel (which is especially evil on embedded platforms).
> - */
> -static inline int is_valid_name(struct elf_info *elf, Elf_Sym *sym)
> -{
> -       const char *name = elf->strtab + sym->st_name;
> -
> -       if (!name || !strlen(name))
> -               return 0;
> -       return !is_arm_mapping_symbol(name);
> -}
> -
>  /*
>   * Find symbols before or equal addr and after addr - in the section sec.
>   * If we find two symbols with equal offset prefer one with a valid name.
> --
> 2.19.1.568.g152ad8e336-goog
>


-- 
Best Regards
Masahiro Yamada