| /* Stack executability handling for GNU dynamic linker. Linux version. |
| Copyright (C) 2003, 2004, 2005, 2006 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, write to the Free |
| Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA |
| 02111-1307 USA. */ |
| |
| #include <ldsodefs.h> |
| #include <sys/mman.h> |
| #include <errno.h> |
| #include <libintl.h> |
| #include <stdbool.h> |
| #include <stackinfo.h> |
| #include <caller.h> |
| #include <sysdep.h> |
| |
| #include <kernel-features.h> |
| |
| |
| extern int __stack_prot attribute_relro attribute_hidden; |
| |
| |
| int |
| internal_function |
| _dl_make_stack_executable (void **stack_endp) |
| { |
| /* This gives us the highest/lowest page that needs to be changed. */ |
| uintptr_t page = ((uintptr_t) *stack_endp |
| & -(intptr_t) GLRO(dl_pagesize)); |
| int result = 0; |
| |
| /* Challenge the caller. */ |
| if (__builtin_expect (__check_caller (RETURN_ADDRESS (0), |
| allow_ldso|allow_libpthread) != 0, 0) |
| || __builtin_expect (*stack_endp != __libc_stack_end, 0)) |
| return EPERM; |
| |
| /* Newer Linux kernels support a flag to make our job easy. */ |
| #if defined PROT_GROWSDOWN || defined PROT_GROWSUP |
| # if __ASSUME_PROT_GROWSUPDOWN == 0 |
| static bool no_growsupdown; |
| if (! no_growsupdown) |
| # endif |
| { |
| if (__builtin_expect (__mprotect ((void *) page, GLRO(dl_pagesize), |
| __stack_prot) == 0, 1)) |
| goto return_success; |
| # if __ASSUME_PROT_GROWSUPDOWN == 0 |
| if (errno == EINVAL) |
| no_growsupdown = true; |
| else |
| # endif |
| { |
| result = errno; |
| goto out; |
| } |
| } |
| #endif |
| |
| /* There is always a hole in the address space below the bottom of the |
| stack. So when we make an mprotect call that starts below the bottom |
| of the stack, it will include the hole and fail with ENOMEM. |
| |
| We start with a random guess at how deep the stack might have gotten |
| so as to have extended the GROWSDOWN mapping to lower pages. */ |
| |
| #if __ASSUME_PROT_GROWSUPDOWN == 0 |
| size_t size = GLRO(dl_pagesize) * 8; |
| |
| # if _STACK_GROWS_DOWN |
| page = page + GLRO(dl_pagesize) - size; |
| while (1) |
| { |
| if (__mprotect ((void *) page, size, |
| __stack_prot & ~PROT_GROWSDOWN) == 0) |
| /* We got this chunk changed; loop to do another chunk below. */ |
| page -= size; |
| else |
| { |
| if (errno != ENOMEM) /* Unexpected failure mode. */ |
| { |
| result = errno; |
| goto out; |
| } |
| |
| if (size == GLRO(dl_pagesize)) |
| /* We just tried to mprotect the top hole page and failed. |
| We are done. */ |
| break; |
| |
| /* Our mprotect call failed because it started below the lowest |
| stack page. Try again on just the top half of that region. */ |
| size /= 2; |
| page += size; |
| } |
| } |
| |
| # elif _STACK_GROWS_UP |
| while (1) |
| { |
| if (__mprotect ((void *) page, size, __stack_prot & ~PROT_GROWSUP) == 0) |
| /* We got this chunk changed; loop to do another chunk below. */ |
| page += size; |
| else |
| { |
| if (errno != ENOMEM) /* Unexpected failure mode. */ |
| { |
| result = errno; |
| goto out; |
| } |
| |
| if (size == GLRO(dl_pagesize)) |
| /* We just tried to mprotect the lowest hole page and failed. |
| We are done. */ |
| break; |
| |
| /* Our mprotect call failed because it extended past the highest |
| stack page. Try again on just the bottom half of that region. */ |
| size /= 2; |
| } |
| } |
| |
| # else |
| # error "Define either _STACK_GROWS_DOWN or _STACK_GROWS_UP" |
| # endif |
| #endif |
| |
| return_success: |
| /* Clear the address. */ |
| *stack_endp = NULL; |
| |
| /* Remember that we changed the permission. */ |
| GL(dl_stack_flags) |= PF_X; |
| |
| out: |
| #ifdef check_consistency |
| check_consistency (); |
| #endif |
| |
| return result; |
| } |
| rtld_hidden_def (_dl_make_stack_executable) |