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elf: Refine direct extern access diagnostics to protected symbol

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Refine commit 349b0441da:

1. Copy relocations for extern protected data do not work properly,
regardless whether GNU_PROPERTY_1_NEEDED_INDIRECT_EXTERN_ACCESS is used.
It makes sense to produce a warning unconditionally.

2. Non-zero value of an undefined function symbol may break pointer
equality, but may be benign in many cases (many programs don't take the
address in the shared object then compare it with the address in the
executable).  Reword the diagnostic to be clearer.

3. Remove the unneeded condition !(undef_map->l_1_needed &
GNU_PROPERTY_1_NEEDED_INDIRECT_EXTERN_ACCESS). If the executable does
not not have GNU_PROPERTY_1_NEEDED_INDIRECT_EXTERN_ACCESS (can only
occur in error cases), the diagnostic should be emitted as well.

When the defining shared object has
GNU_PROPERTY_1_NEEDED_INDIRECT_EXTERN_ACCESS, report an error to apply
the intended enforcement.
This commit is contained in:
Fangrui Song 2022-06-14 13:07:27 -07:00
parent 876cdf517d
commit 7374c02b68
1 changed files with 27 additions and 23 deletions
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50
sysdeps/generic/dl-protected.h
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@ -26,29 +26,33 @@ _dl_check_protected_symbol (const char *undef_name,
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"));
}
if (undef_map == NULL || undef_map->l_type != lt_executable)
return;
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_error_printf ("warning: copy relocation against non-copyable "
"protected symbol `%s' in `%s'\n",
undef_name, map->l_name);
else if ((type_class & ELF_RTYPE_CLASS_PLT) && ref->st_value != 0
&& ref->st_shndx == SHN_UNDEF)
/* 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_error_printf (
"warning: direct reference to "
"protected function `%s' in `%s' may break pointer equality\n",
undef_name, map->l_name);
else
return;
if (map->l_1_needed & GNU_PROPERTY_1_NEEDED_INDIRECT_EXTERN_ACCESS)
_dl_signal_error (
0, map->l_name, undef_name,
N_ ("error due to GNU_PROPERTY_1_NEEDED_INDIRECT_EXTERN_ACCESS"));
}
#endif /* _DL_PROTECTED_H */