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Subject[PATCH] binfmt_elf.c SIGILL with large external static array on PPC64
Date
When using the follow code compiled as an ELF32 binary on a PPC64 machine, application terminates with a SIGILL.
<source code of C Application>
int x[3000][3000][30];
int main() {
return 0;
}
Platform: Linux-2.6.0-test11 on PPC64

Comments: The problem is that we don't reserve the bss region for the app (via a set_brk/do_brk call) until after we've loaded the
loader so they get mapped to overlapping memory locations. The fix is to move the set_brk/do_brk call to before the point we call
load_elf_interp().
Here's a patch. This gives a clearer error message and terminates with a SEGFAULT. Though I'm not sure if a large external array
could be the only trigger for this. I'd appreciate your comments/suggestions.
In case of difficulty in applying the patch enclosed, you could find it at
http://www.geocities.com/ssrikrishnan/binfmtelf.htm

Thanks,
Srikrishnan

--- linux-2.6.0-test11/fs/binfmt_elf.c 2003-12-16 18:50:46.000000000 +0530
+++ linux-2.6.0-test11.patched/fs/binfmt_elf.c 2003-12-16 18:58:51.000000000 +0530
@@ -82,13 +82,15 @@

#define BAD_ADDR(x) ((unsigned long)(x) > TASK_SIZE)

-static void set_brk(unsigned long start, unsigned long end)
+static unsigned long set_brk(unsigned long start, unsigned long end)
{
+ unsigned long retval;
start = ELF_PAGEALIGN(start);
end = ELF_PAGEALIGN(end);
if (end > start)
- do_brk(start, end - start);
+ retval = do_brk(start, end - start);
current->mm->start_brk = current->mm->brk = end;
+ return retval;
}


@@ -737,6 +739,19 @@
start_data += load_bias;
end_data += load_bias;

+ /* Calling set_brk effectively mmaps the pages that we need
+ * for the bss and break sections. We must do this before
+ * before we load the interpreter, in case we have a
+ * huge bss region.
+ */
+ if(BAD_ADDR(set_brk(elf_bss, elf_brk)) {
+ printk(KERN_ERR "unable to map bss region \n");
+ send_sig(SIGSEGV, current, 0);
+ goto out_free_dentry;
+
+ }
+
+ padzero(elf_bss);
if (elf_interpreter) {
if (interpreter_type == INTERPRETER_AOUT)
elf_entry = load_aout_interp(&interp_ex,
@@ -782,13 +797,6 @@
current->mm->end_data = end_data;
current->mm->start_stack = bprm->p;

- /* Calling set_brk effectively mmaps the pages that we need
- * for the bss and break sections
- */
- set_brk(elf_bss, elf_brk);
-
- padzero(elf_bss);
-
if (current->personality & MMAP_PAGE_ZERO) {
/* Why this, you ask??? Well SVr4 maps page 0 as read-only,
and some applications "depend" upon this behavior.
-
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