metag: Reduce maximum stack size to 256MB

Specify the maximum stack size for arches where the stack grows upward
(parisc and metag) in asm/processor.h rather than hard coding in
fs/exec.c so that metag can specify a smaller value of 256MB rather than
1GB.

This fixes a BUG on metag if the RLIMIT_STACK hard limit is increased
beyond a safe value by root. E.g. when starting a process after running
"ulimit -H -s unlimited" it will then attempt to use a stack size of the
maximum 1GB which is far too big for metag's limited user virtual
address space (stack_top is usually 0x3ffff000):

BUG: failure at fs/exec.c:589/shift_arg_pages()!

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Helge Deller <deller@gmx.de>
Cc: "James E.J. Bottomley" <jejb@parisc-linux.org>
Cc: linux-parisc@vger.kernel.org
Cc: linux-metag@vger.kernel.org
Cc: John David Anglin <dave.anglin@bell.net>
Cc: stable@vger.kernel.org # only needed for >= v3.9 (arch/metag)

1 files changed, 3 insertions, 3 deletions

diff --git a/fs/exec.c b/fs/exec.c
index 476f3ebf437e..238b7aa26f68 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -657,10 +657,10 @@ int setup_arg_pages(struct linux_binprm *bprm,
         unsigned long rlim_stack;
 
 #ifdef CONFIG_STACK_GROWSUP
-        /* Limit stack size to 1GB */
+        /* Limit stack size */
         stack_base = rlimit_max(RLIMIT_STACK);
-        if (stack_base > (1 << 30))
-                stack_base = 1 << 30;
+        if (stack_base > STACK_SIZE_MAX)
+                stack_base = STACK_SIZE_MAX;
 
         /* Make sure we didn't let the argument array grow too large. */
         if (vma->vm_end - vma->vm_start > stack_base)