elf: Enable relro for static build

The code is similar to the one at elf/dl-reloc.c, where it checks for
the l_relro_size from the link_map (obtained from PT_GNU_RELRO header
from program headers) and calls_dl_protected_relro.

For testing I will use the ones proposed by Florian's patch
'elf: Add tests for working RELRO protection' [1].

Checked on x86_64-linux-gnu, i686-linux-gnu, powerpc64le-linux-gnu,
aarch64-linux-gnu, s390x-linux-gnu, and sparc64-linux-gnu.  I also
check with --enable-static pie on x86_64-linux-gnu, i686-linux-gnu,
and aarch64-linux-gnu which seems the only architectures where
static PIE is actually working (as per 9d7a3741c9e, on
arm-linux-gnueabihf, powerpc64{le}-linux-gnu, and s390x-linux-gnu
I am seeing runtime issues not related to my patch).

[1] https://sourceware.org/ml/libc-alpha/2019-10/msg00059.html

Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

diff --git a/elf/dl-support.c b/elf/dl-support.c
index 957a810938c37fccb630515648c46253f410f74c..508a5c1196dbb5c613ecd85b93139f2a19a1542b 100644 (file)
--- a/elf/dl-support.c
+++ b/elf/dl-support.c
@@ -367,14 +367,24 @@ _dl_non_dynamic_init (void)
   if (_dl_platform != NULL)
     _dl_platformlen = strlen (_dl_platform);
 
-  /* Scan for a program header telling us the stack is nonexecutable.  */
   if (_dl_phdr != NULL)
-    for (uint_fast16_t i = 0; i < _dl_phnum; ++i)
-      if (_dl_phdr[i].p_type == PT_GNU_STACK)
+    for (const ElfW(Phdr) *ph = _dl_phdr; ph < &_dl_phdr[_dl_phnum]; ++ph)
+      switch (ph->p_type)
        {
-         _dl_stack_flags = _dl_phdr[i].p_flags;
+       /* Check if the stack is nonexecutable.  */
+       case PT_GNU_STACK:
+         _dl_stack_flags = ph->p_flags;
+         break;
+
+       case PT_GNU_RELRO:
+         _dl_main_map.l_relro_addr = ph->p_vaddr;
+         _dl_main_map.l_relro_size = ph->p_memsz;
          break;
        }
+
+  /* Setup relro on the binary itself.  */
+  if (_dl_main_map.l_relro_size != 0)
+    _dl_protect_relro (&_dl_main_map);
 }
 
 #ifdef DL_SYSINFO_IMPLEMENTATION