[patch] x86_64: enlarge window for stack growth

[Chuck Ebbert <76306.1226@compuserve.com>]

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>

--- 2.6.17-rc6-64.orig/arch/x86_64/mm/fault.c
+++ 2.6.17-rc6-64/arch/x86_64/mm/fault.c
@@ -410,8 +410,10 @@ asmlinkage void __kprobes do_page_fault(
 	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))
-- 
Chuck
 "You can't read a newspaper if you can't read."  --George W. Bush
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