Re: [PATCH 2/2] Add run-time chesk for indirect external access

[Adhemerval Zanella via Libc-alpha <libc-alpha@sourceware.org>]

On 03/08/2021 18:59, H.J. Lu via Libc-alpha wrote:
> When performing symbol lookup for references in executable without
> indirect external access:
> 
> 1. Disallow copy relocations in executable against protected data symbols
> in a shared object with indirect external access.
> 2. Disallow non-zero symbol values of undefined function symbols in
> executable, which are used as the function pointer, against protected
> function symbols in a shared object with indirect external access.

How hard would to add some testcases for both cases?  To simplify we may
want to build it iff binutins supports noindirect-extern-access.

The rest LGTM, just a nit below due an ununsed variable.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

> ---
>  elf/dl-lookup.c                |  5 ++++
>  sysdeps/generic/dl-protected.h | 54 ++++++++++++++++++++++++++++++++++
>  2 files changed, 59 insertions(+)
>  create mode 100644 sysdeps/generic/dl-protected.h
> 
> diff --git a/elf/dl-lookup.c b/elf/dl-lookup.c
> index eea217eb28..430359af39 100644
> --- a/elf/dl-lookup.c
> +++ b/elf/dl-lookup.c
> @@ -24,6 +24,7 @@
>  #include <ldsodefs.h>
>  #include <dl-hash.h>
>  #include <dl-machine.h>
> +#include <dl-protected.h>
>  #include <sysdep-cancel.h>
>  #include <libc-lock.h>
>  #include <tls.h>
> @@ -527,6 +528,10 @@ do_lookup_x (const char *undef_name, uint_fast32_t new_hash,
>  	  if (__glibc_unlikely (dl_symbol_visibility_binds_local_p (sym)))
>  	    goto skip;
>  
> +	  if (ELFW(ST_VISIBILITY) (sym->st_other) == STV_PROTECTED)
> +	    _dl_check_protected_symbol (undef_name, undef_map, ref, map,
> +					type_class);
> +
>  	  switch (ELFW(ST_BIND) (sym->st_info))
>  	    {
>  	    case STB_WEAK:

Ok.

> diff --git a/sysdeps/generic/dl-protected.h b/sysdeps/generic/dl-protected.h
> new file mode 100644
> index 0000000000..244d020dc4
> --- /dev/null
> +++ b/sysdeps/generic/dl-protected.h
> @@ -0,0 +1,54 @@
> +/* Support for STV_PROTECTED visibility.  Generic version.
> +   Copyright (C) 2021 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#ifndef _DL_PROTECTED_H
> +#define _DL_PROTECTED_H
> +
> +static inline void __attribute__ ((always_inline))
> +_dl_check_protected_symbol (const char *undef_name,

This argument seems unused.

> +			    const struct link_map *undef_map,
> +			    const ElfW(Sym) *ref,
> +			    const struct link_map *map,
> +			    int type_class)
> +{
> +  if (undef_map != NULL
> +      && undef_map->l_type == lt_executable
> +      && !(undef_map->l_1_needed
> +	   & GNU_PROPERTY_1_NEEDED_INDIRECT_EXTERN_ACCESS)
> +      && (map->l_1_needed
> +	  & GNU_PROPERTY_1_NEEDED_INDIRECT_EXTERN_ACCESS))
> +    {
> +      if ((type_class & ELF_RTYPE_CLASS_COPY))
> +	/* Disallow copy relocations in executable against protected
> +	   data symbols in a shared object which needs indirect external
> +	   access.  */
> +	_dl_signal_error (0, map->l_name, undef_name,
> +			  N_("copy relocation against non-copyable protected symbol"));
> +      else if (ref->st_value != 0
> +	       && ref->st_shndx == SHN_UNDEF
> +	       && (type_class & ELF_RTYPE_CLASS_PLT))
> +	/* Disallow non-zero symbol values of undefined symbols in
> +	   executable, which are used as the function pointer, against
> +	   protected function symbols in a shared object with indirect
> +	   external access.  */
> +	_dl_signal_error (0, map->l_name, undef_name,
> +			  N_("non-canonical reference to canonical protected function"));
> +    }
> +}
> +
> +#endif /* _DL_PROTECTED_H */
> 

Ok.