Re: Useless stack randomization patch

[Franck Bui-Huu <vagabon.xyz@gmail.com>]

Ralf Baechle wrote:
> On Wed, Sep 26, 2007 at 04:10:14PM +0200, Franck Bui-Huu wrote:
> I suppose we should give it a sane definition.  Not sure what would be
> useful, if it should be like an ASCII string with the processor type or
> more corse grained like just "mips32r2", should ASEs be mentioned ...
> 

Well before giving any sane definition, shouldn't we know why this
dependency (ELF_PLATFORM/sp-randomization) exists at all...

Is something like the patch below better ?

		Franck

-- 8< --


diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 43143c5..e8713fb 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -150,6 +150,13 @@ create_elf_tables(struct linux_binprm *bprm, struct elfhdr *exec,
 	struct vm_area_struct *vma;
 
 	/*
+	 * In some cases (e.g. Hyper-Threading), we want to avoid L1
+	 * evictions by the processes running on the same package. One
+	 * thing we can do is to shuffle the initial stack for them.
+	 */
+	p = arch_align_stack(p);
+
+	/*
 	 * If this architecture has a platform capability string, copy it
 	 * to userspace.  In some cases (Sparc), this info is impossible
 	 * for userspace to get any other way, in others (i386) it is
@@ -159,14 +166,6 @@ create_elf_tables(struct linux_binprm *bprm, struct elfhdr *exec,
 	if (k_platform) {
 		size_t len = strlen(k_platform) + 1;
 
-		/*
-		 * In some cases (e.g. Hyper-Threading), we want to avoid L1
-		 * evictions by the processes running on the same package. One
-		 * thing we can do is to shuffle the initial stack for them.
-		 */
-
-		p = arch_align_stack(p);
-
 		u_platform = (elf_addr_t __user *)STACK_ALLOC(p, len);
 		if (__copy_to_user(u_platform, k_platform, len))
 			return -EFAULT;