Re: [PATCH v7 03/25] kallsyms: increase maximum kernel symbol length to 512

[Jarkko Sakkinen]

On Mon, May 23, 2022 at 04:01:16AM +0200, Miguel Ojeda wrote:
> Rust symbols can become quite long due to namespacing introduced
> by modules, types, traits, generics, etc. For instance,
> the following code:
> 
>     pub mod my_module {
>         pub struct MyType;
>         pub struct MyGenericType<T>(T);
> 
>         pub trait MyTrait {
>             fn my_method() -> u32;
>         }
> 
>         impl MyTrait for MyGenericType<MyType> {
>             fn my_method() -> u32 {
>                 42
>             }
>         }
>     }
> 
> generates a symbol of length 96 when using the upcoming v0 mangling scheme:
> 
>     _RNvXNtCshGpAVYOtgW1_7example9my_moduleINtB2_13MyGenericTypeNtB2_6MyTypeENtB2_7MyTrait9my_method
> 
> At the moment, Rust symbols may reach up to 300 in length.
> Setting 512 as the maximum seems like a reasonable choice to
> keep some headroom.

There's no description what the patch does.

> 
> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
> Reviewed-by: Petr Mladek <pmladek@xxxxxxxx>
> Co-developed-by: Alex Gaynor <alex.gaynor@xxxxxxxxx>
> Signed-off-by: Alex Gaynor <alex.gaynor@xxxxxxxxx>
> Co-developed-by: Wedson Almeida Filho <wedsonaf@xxxxxxxxxx>
> Signed-off-by: Wedson Almeida Filho <wedsonaf@xxxxxxxxxx>
> Co-developed-by: Gary Guo <gary@xxxxxxxxxxx>
> Signed-off-by: Gary Guo <gary@xxxxxxxxxxx>
> Co-developed-by: Boqun Feng <boqun.feng@xxxxxxxxx>
> Signed-off-by: Boqun Feng <boqun.feng@xxxxxxxxx>
> Signed-off-by: Miguel Ojeda <ojeda@xxxxxxxxxx>
> ---
> This is a prerequisite patch, independently submitted at:
> 
>     https://lore.kernel.org/lkml/20220506203443.24721-4-ojeda@xxxxxxxxxx/
> 
>  include/linux/kallsyms.h            | 2 +-
>  kernel/livepatch/core.c             | 4 ++--
>  scripts/kallsyms.c                  | 4 ++--
>  tools/include/linux/kallsyms.h      | 2 +-
>  tools/lib/perf/include/perf/event.h | 2 +-
>  tools/lib/symbol/kallsyms.h         | 2 +-
>  6 files changed, 8 insertions(+), 8 deletions(-)
> 
> diff --git a/include/linux/kallsyms.h b/include/linux/kallsyms.h
> index ce1bd2fbf23e..e5ad6e31697d 100644
> --- a/include/linux/kallsyms.h
> +++ b/include/linux/kallsyms.h
> @@ -15,7 +15,7 @@
>  
>  #include <asm/sections.h>
>  
> -#define KSYM_NAME_LEN 128
> +#define KSYM_NAME_LEN 512
>  #define KSYM_SYMBOL_LEN (sizeof("%s+%#lx/%#lx [%s %s]") + \
>  			(KSYM_NAME_LEN - 1) + \
>  			2*(BITS_PER_LONG*3/10) + (MODULE_NAME_LEN - 1) + \
> diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> index bc475e62279d..ec06ce59d728 100644
> --- a/kernel/livepatch/core.c
> +++ b/kernel/livepatch/core.c
> @@ -213,7 +213,7 @@ static int klp_resolve_symbols(Elf_Shdr *sechdrs, const char *strtab,
>  	 * we use the smallest/strictest upper bound possible (56, based on
>  	 * the current definition of MODULE_NAME_LEN) to prevent overflows.
>  	 */
> -	BUILD_BUG_ON(MODULE_NAME_LEN < 56 || KSYM_NAME_LEN != 128);
> +	BUILD_BUG_ON(MODULE_NAME_LEN < 56 || KSYM_NAME_LEN != 512);
>  
>  	relas = (Elf_Rela *) relasec->sh_addr;
>  	/* For each rela in this klp relocation section */
> @@ -227,7 +227,7 @@ static int klp_resolve_symbols(Elf_Shdr *sechdrs, const char *strtab,
>  
>  		/* Format: .klp.sym.sym_objname.sym_name,sympos */
>  		cnt = sscanf(strtab + sym->st_name,
> -			     ".klp.sym.%55[^.].%127[^,],%lu",
> +			     ".klp.sym.%55[^.].%511[^,],%lu",
>  			     sym_objname, sym_name, &sympos);
>  		if (cnt != 3) {
>  			pr_err("symbol %s has an incorrectly formatted name\n",
> diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
> index 7e99799aa7b9..275044b840dc 100644
> --- a/scripts/kallsyms.c
> +++ b/scripts/kallsyms.c
> @@ -30,10 +30,10 @@
>  #define _stringify_1(x)	#x
>  #define _stringify(x)	_stringify_1(x)
>  
> -#define KSYM_NAME_LEN		128
> +#define KSYM_NAME_LEN		512
>  
>  /* A substantially bigger size than the current maximum. */
> -#define KSYM_NAME_LEN_BUFFER	512
> +#define KSYM_NAME_LEN_BUFFER	2048
>  _Static_assert(
>  	KSYM_NAME_LEN_BUFFER == KSYM_NAME_LEN * 4,
>  	"Please keep KSYM_NAME_LEN_BUFFER in sync with KSYM_NAME_LEN"
> diff --git a/tools/include/linux/kallsyms.h b/tools/include/linux/kallsyms.h
> index efb6c3f5f2a9..5a37ccbec54f 100644
> --- a/tools/include/linux/kallsyms.h
> +++ b/tools/include/linux/kallsyms.h
> @@ -6,7 +6,7 @@
>  #include <stdio.h>
>  #include <unistd.h>
>  
> -#define KSYM_NAME_LEN 128
> +#define KSYM_NAME_LEN 512
>  
>  struct module;
>  
> diff --git a/tools/lib/perf/include/perf/event.h b/tools/lib/perf/include/perf/event.h
> index e7758707cadd..116a80c31675 100644
> --- a/tools/lib/perf/include/perf/event.h
> +++ b/tools/lib/perf/include/perf/event.h
> @@ -95,7 +95,7 @@ struct perf_record_throttle {
>  };
>  
>  #ifndef KSYM_NAME_LEN
> -#define KSYM_NAME_LEN 256
> +#define KSYM_NAME_LEN 512
>  #endif
>  
>  struct perf_record_ksymbol {
> diff --git a/tools/lib/symbol/kallsyms.h b/tools/lib/symbol/kallsyms.h
> index 72ab9870454b..542f9b059c3b 100644
> --- a/tools/lib/symbol/kallsyms.h
> +++ b/tools/lib/symbol/kallsyms.h
> @@ -7,7 +7,7 @@
>  #include <linux/types.h>
>  
>  #ifndef KSYM_NAME_LEN
> -#define KSYM_NAME_LEN 256
> +#define KSYM_NAME_LEN 512
>  #endif
>  
>  static inline u8 kallsyms2elf_binding(char type)
> -- 
> 2.36.1
> 

BR, Jarkko