[PATCH] x86_64: enlarge window for stack growth

Allow stack growth so the 'enter' instruction works.  Also
fixes problem in compat_sys_kexec_load() which could allocate
more than 128 bytes using compat_alloc_user_space().

Signed-off-by: Chuck Ebbert <76306.1226@compuserve.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 4 insertions, 2 deletions

diff --git a/arch/x86_64/mm/fault.c b/arch/x86_64/mm/fault.c
index 64728898f869..4968a71df4aa 100644
--- a/arch/x86_64/mm/fault.c
+++ b/arch/x86_64/mm/fault.c
@@ -410,8 +410,10 @@ asmlinkage void __kprobes do_page_fault(struct pt_regs *regs,
         if (!(vma->vm_flags & VM_GROWSDOWN))
                 goto bad_area;
         if (error_code & 4) {
-                // XXX: align red zone size with ABI 
-                if (address + 128 < regs->rsp)
+                /* Allow userspace just enough access below the stack pointer
+                 * to let the 'enter' instruction work.
+                 */
+                if (address + 65536 + 32 * sizeof(unsigned long) < regs->rsp)
                         goto bad_area;
         }
         if (expand_stack(vma, address))