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/* Check if range is within a read-only from a loaded ELF object.
Copyright (C) 2025 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/>. */
#include <ldsodefs.h>
static bool
check_relro (const struct link_map *l, uintptr_t start, uintptr_t end)
{
if (l->l_relro_addr != 0)
{
uintptr_t relro_start = ALIGN_DOWN (l->l_addr + l->l_relro_addr,
GLRO(dl_pagesize));
uintptr_t relro_end = ALIGN_DOWN (l->l_addr + l->l_relro_addr
+ l->l_relro_size,
GLRO(dl_pagesize));
/* RELRO is caved out from a RW segment, so the next range is either
RW or nonexistent. */
return relro_start <= start && end <= relro_end
? dl_readonly_area_rdonly : dl_readonly_area_writable;
}
return dl_readonly_area_writable;
}
enum dl_readonly_area_error_type
_dl_readonly_area (const void *ptr, size_t size)
{
struct dl_find_object dlfo;
if (_dl_find_object ((void *)ptr, &dlfo) != 0)
return dl_readonly_area_not_found;
const struct link_map *l = dlfo.dlfo_link_map;
uintptr_t ptr_start = (uintptr_t) ptr;
uintptr_t ptr_end = ptr_start + size;
for (const ElfW(Phdr) *ph = l->l_phdr; ph < &l->l_phdr[l->l_phnum]; ++ph)
if (ph->p_type == PT_LOAD)
{
/* For segments with alignment larger than the page size,
_dl_map_segment allocates additional space that is mark as
PROT_NONE (so we can ignore). */
uintptr_t from = l->l_addr
+ ALIGN_DOWN (ph->p_vaddr, GLRO(dl_pagesize));
uintptr_t to = l->l_addr
+ ALIGN_UP (ph->p_vaddr + ph->p_filesz, GLRO(dl_pagesize));
/* Found an entry that at least partially covers the area. */
if (from < ptr_end && to > ptr_start)
{
if (ph->p_flags & PF_W)
return check_relro (l, ptr_start, ptr_end);
if ((ph->p_flags & PF_R) == 0)
return dl_readonly_area_writable;
if (from <= ptr_start && to >= ptr_end)
return dl_readonly_area_rdonly;
else if (from <= ptr_start)
size -= to - ptr_start;
else if (to >= ptr_end)
size -= ptr_end - from;
else
size -= to - from;
if (size == 0)
break;
}
}
return size == 0 ? dl_readonly_area_rdonly : dl_readonly_area_not_found;
}
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